Filter Boss Fuel Protection System


Regular readers of this site will know that I take a more than passing interest in fuel quality and our dependence on engine reliability. I believe that these are matters that go to the heart of modern cruising. Therefore, I also believe that anything that can offer improvements in terms of engine reliability has got to be worth serious consideration.

When we ordered Pèlerin, we specified a twin Racor fuel pre-filter system that would allow us to switch from one filter to the other in the event of a filter becoming clogged. This simple, basic system can be a life saver in the worst of circumstances, and I’m always surprised that it isn’t more widely adopted, as it’s a relatively low cost option (especially at build).

But the system we had was less than ideal, due to the fact that the wrong filters were installed (we had thought we were getting the Racor Turbine filters). The filters that were installed, whilst serviceable, are far less effective at dealing with water, and take more time and effort to change.

In addition, the standard fuel system had a common return from the engine to the tanks, making it effectively impossible to isolate one tank from the other in the event of one being affected by bad fuel – not a great idea.  In practice it all worked, but we had long discussed improving the system.

Then an offer came in to Attainable Adventure Cruising from KTI Systems Inc. to test one of their modular Filter Boss fuel filtration/polishing systems. John and Phyllis already had their own designed system aboard Morgans Cloud and were happy with it, but knowing that we had concerns over our set-up, they suggested that we should try the system aboard Pèlerin, an offer that we rapidly accepted.

Commander 60

We contacted Andy Keenan of KTI Systems to establish the most suitable model and installation for our boat. Going on the horsepower (55hp) of our Volvo engine and in view of Pèlerin’s use as our ocean cruising home, he advised us to go for their FilterBoss Commander FC60. This is one of their top of the range systems, three versions of which are available to suit engines with fuel demands of 60, 90 and 120 gallons per hour.


As is our usual preference, I like to be involved in the installation of any new equipment, working on the principle that it’ll be me who’ll be working on it down the line. Due to the complexity of replacing most of the fuel piping in order to isolate each fuel tank, we employed the services of local engineer Jean-Michel Alliot at Puerto Calero, Lanzarote (who we’d readily recommend) to assist.

Once we’d established a site for the new unit, the installation proved straightforward. This was greatly helped by a first class product manual, one of the best (if not the best) I’ve ever seen (other manufacturers, please note!).  Secondly, as the unit comes from the factory solidly mounted and all piping connecting the various components of the unit are in place, the rest of the installation basically consists of connecting up the various pipes to and from the tanks and wiring the pump and the warning devices.

Sensibly, rather than try and reinvent the wheel, KTI Systems use the impeccable Racor 500MA turbine filters, which are simply the best that there are in my experience for fuel cleaning, water separation and ease of changing filters. The rest of the hardware supplied appears to be of equal quality, and the whole module is neat and robust.


controlThe heart of any such system is the ability to switch from one clogging filter to a fresh, clean one as quickly as possible, circumventing the chance of some heart-stopping, worst case scenario as the engine falters and stops. Not only does the Commander system make this as easy as possible by having a single lever control to make the switch, it also incorporates an audible (loud – excellent!) and visual warning module that operates as the filter begins to clog, warning you in advance of a potential problem – smart.

An optional extra is to fit a remote electrical switch (perhaps mounted at the helm) to allow the filters to be changed at the flick of a finger, but personally I’m happy with something simple and mechanical. Sensibly the unit also has a non-return valve built in to stop air locks entering the system when the boat is heeled hard over or when the tanks are low – I can think of more than one occasion where this has happened to me.

Using the integral electric fuel pump, fuel can be polished (filtered) when at rest, and fuel quality can be monitored as the nozzle is in the filler. It also allows fuel to be transferred from one tank to another, makes for really easy bleeding of the engine, and can even be used as a back-up if the engine driven lift pump weakens or fails, both of which I’ve had happen in the past.

with light

The vacuum gauge allows for an instant visual check to be made on the state of the filter in use, and we’ve now incorporated this as a regular check in our daily maintenance regime. It also allows the owner to conduct a vacuum test of the fuel supply side to identify and isolate any fuel or air leaks between the tank and the unit. We have installed our Commander in our aft services cabin where it’s easy to view and change filters, but KTI have sensibly installed a filter light, that allows inspection of the fuel condition even if the unit is mounted in a low light area.

How has it performed?

One thing that is always a risk when you install some new, sophisticated device is that it will highlight flaws in your existing system. Such was the case with this installation, as we discovered that the fuel shut off valves at both of our tanks were admitting air into the fuel system as a result of being over-tightened. The diagnostic capability of the Commander allowed us to identify the problem and, if not immediately correct it, at least make the system air tight and serviceable, so that we could confidently set off across the Atlantic. We now use the diagnostic function on a regular basis to check the fuel system for leaks, which gives us real peace of mind.

Every function performs as promised, top quality parts (Walbro pump, Racor filters) have been used throughout, and the whole unit is robust and well made in the right materials. It incorporates a multitude of useful features, but thankfully no gimmicks, and it is obvious that the whole unit has been thoroughly thought through from the design stage to final delivery.

As I already outlined, the manual is exemplary, and KTI Systems were extremely helpful as we sought to diagnose and correct our fuel valve problem, via phone and email, which is exactly as it should be for those of us who voyage under sail around the world.


Most long-distance cruisers are rightly fanatical about the quality of the fuel they are taking on board, especially in remote places where it’s almost impossible to know its provenance. But if the fuel is dirty, once it’s in the tank, there’s not much you can do except dump it or keep changing the filters – that is, if you find out about it before the engine quits on you. This is where the FilterBoss Commander system can really make a contribution, and therefore gets my whole-hearted approval.

Our model retails at US $2160, although KTI Systems can supply simpler versions that incorporate some, if not all, of the features of our unit at less cost. In my view, anyone specifying the fuel system on a new boat, or re-fitting an older boat, would do well to take a close look at one of these units, appropriate for the type of cruising that they plan to do.


KTI Systems Inc. kindly supplied the FilterBoss Commander Unit free of charge for us to test. We paid all the air freight charges and the cost of installation and ancillary materials. [KTI Systems is sponsor of Attainable Adventure Cruising. See sidebar advertisement.]

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Colin, European Correspondent here at AAC, is a deeply experienced offshore sailor who holds a Yachtmaster licence, and a gifted photographer and talented writer who has added a whole new dimension to Attainable Adventure Cruising. In addition, since Colin and Louise are from England and had their OVNI 435, Pèlerin built in France, they bring a European perspective to our site. You can read more about Colin and Louise and their business at their website.

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Andy Keenan


The article was well written, and please keep in touch with us as you travel closer to the Bahamas.

Thank you

Andy Keenan

Dick Stevenson

Nice article. Looks to be a nice piece of kit. Its foundation appears to be Racor’s dual filter assembly which we have been using for 12 years or so and have been very happy with. I have received conflicting suggestions over the years on the vacuum gauge and at what degree of vacuum to start to worry or switch to the other filter. Did you get guidelines in that area? Fortunately we have had clean fuel and so have not really had filters that clogged up (so far).
Thanks, Dick Stevenson, s/v Alchemy

John Harries

Hi Dick,

I can help with that. I don’t recommend the Racor vacuum gauges that fit on top of the filters in place of the T handles. I tried them for a while and got air leaks on two of them. Maybe I was unlucky, but I think they are more trouble than they are worth.

If it were me, I would buy one of the FilterBoss early warning systems.

I would then follow FilterBoss’s recommendation on the vacuum reading that indicates a filter change.

John Harries

Hi Colin,

Great post with a lot of really good information, thank you, as always. In fact you have me so convinced that I’m thinking of replacing our 15 year old home brewed system, which needs work, with one of these.

One of the things that impresses me, as a long term user of Racor 500 filter, is the way in which Andy and company have improved on the details. For example the drain valve on a standard Racor 500 is a plastic piece of junk that will leak air or fuel after a while, and that is very messy to drain. I see that the FilterBoss has fixed this with a couple of proper metal drain valves.


We met Andy at Green Turtle Cay last year, but missed him this time. He’s a good guy in addition to delivering a good product.

Dick Stevenson

Understood and agree about the top of the T handle gauges. They are also very vulnerable to getting bumped by people working in tight places maybe explaining, and certainly contributing, to their propensity to the air leaks you reported occurring.
However, my Dual Racor system appears to be exactly the foundation Filter Boss uses. My vacuum gauge is mounted stoutly on a milled metal block protected between the 2 filters just as in Colin’s picture. Further, just to be fair to Racor, the metal petcocks (drain valves) on the bottom that you admire are on my 12 year old Racor assembly just as pictured. I remember those old plastic bowl drains and they were awkward and messy. The metal ones are far superior.
So still curious about what Filter Boss recommends with respect to the reading of the vacuum gauges? Or how do others w/ vacuum gauges in their fuel systems use their gauge data?
Thanks, Dick Stevenson, s/v Alchemy


Dick, 2 cents worth. We have a two filter, two tank crossover manifold and polishing system that predates Filter Boss. However, at the core, they are essentially the same. Our Racor vacuum gauge is plumbed so that it provides information on which ever filter is in use. Having said that, I don’t find the Racor gauges particularly useful. They are so small, they are essentially good/bad indicators. Even then, I can hear the Walbro polishing pump laboring before the gauge says “game over, out of time.”

Still, we have been using these gauges since 1977. In all that time I have never seen one that indicated better than “yellow” with a fresh 2 micron filter element. We have decided to replace ours with an oil filled gauge no less than 2 inches in diameter, and we will assign our own color boundaries.

A casual, on the dock, anecdotal survey here in Marsh Harbour finds most people changing filters based on time or events rather than gauge indications. Compared to the price of diesel, replacing elements at refueling is pretty cheap. Also doing this can help isolate whether fuel problems are arising from long term tank conditions or a bad load of fuel.

John Harries

Hi Chris,

That’s a good point about the Racor gauges not being very accurate. Our experience has been the same. Although I would say that having a gauge comes into its own when you get a load of marginal fuel. This has happened to us three times in the north over the years and being able to tell when the filters need changing let us balance our supply of filters against the problem more accurately, as we cleaned up the fuel by polishing. The point being that using the gauge we were able to get a lot more sediment out with each filter even after the pump started to slow. The gauge also allowed us to monitor the engine filter which needed changing more frequently than normal, even after the fuel was polished.


Hi John,
Indeed! That’s why we’ve decided something larger and more informative would be a good idea. We’d much rather get the full lifetime out of a filter. The gauge I’m looking at is like a barometer. It has an adjustable free hand so one can see where the last reading was. Separ makes one, but we’d like a larger diameter — 3in min.

Dick Stevenson

Colin and everyone,
There appears to be at least 2 good reasons to polish/clean fuel. One is well addressed by Filter Boss while the other remains elusive to those fuel polishing systems that rely on the fuel pick up tube. That access leaves the bottom few inches of the tank uncleaned. The second reason is to protect metal fuel tanks. It is my take that metal fuel tanks would last a lot longer if their bottom corner did not harbour accumulated water dirt etc. etc. Left to stew over years and years, pinhole leaks occur. I am fortunate in having access to the lower corner and do my polishing by drawing fuel from that region below the pickup tube. My hope is that the life of the tank will be increased. It is something to keep in mind when playing with fuel polishing systems. Most tanks (and their installations) prove too daunting a challenge: the time to consider this is when ordering new tanks.
Dick Stevenson, s/v Alchemy

Dick Stevenson

Dear Colin,
I am sorry you received the wrong Racor Dual Filter assembly at the outset. I know how diligent you and Lou are and it must have been infuriating to have discovered the error. I will be interested in your feedback on the fuel quality (I guess I am making a suggestion) you find in South America.
On Alchemy, we have spent time in Central America, the Middle East, and lots of similarly out of the way places in between. Places where one might suspect to find dirty, wet fuel. In that time we have jerry canned multiple times, drained 55 gal drums at least once and gotten fuel at the usual fishing wharfs and marina fuel depots everywhere. We do not generally use a Baja filter (or the like). (It is so terribly slow, hard not to spill, and my personal inner whimp shows itself, in this of many ways, in dealing with the impatience of waiting boats to get fuelled and the diesel jockeys who want me out of there.) We polish fuel (taking from the bottom of the tank, running it through a Racor and back into the top) 3-6 times a year depending on consumption, more often if there is any reason to question the fuel.
I know there are a number of disaster stories that can be trotted out, but we have had no evidence of problematic fuel in. Our polishing filter certainly looks dirty after a couple years of polishing, but is in no way clogged. Similarly our pre-filter looks dirty when we periodically change it while remaining far from clogged.
Coming off of the above personal observations, I would consider questioning the Filter Boss’s practicality for most of us. The FB you describe serves 3 main functions: filtering (with the possibility of quick filter changes when clogs occur) , polishing, and monitoring/alarms.
Filtering: I believe the practicality of dual filters with the capacity to change filters at the flip of a lever is beyond question. This is covered by a Dual Racor filter assembly, also the foundation of the FB assembly.
Polishing: My experience is that polishing certainly cleans the fuel, but in all my polishing I have never found debris that would have clogged the filter and/or stopped the engine (5,000+ gal/ 5000 engine 2,000 genset hours) . In any event, flipping to the second filter would solve clogging in the vast majority of cases. I continue my polishing at this point to clean the area in the low corner below the pick up tube (for the fuel tanks sake) as much as to polish the fuel for diesel consumption. This area the FB does not get to.
Monitoring/alarms: I am into the engine area at regular intervals while on motoring runs. I always have a flashlight in hand doing so and, although a dedicated light might be nice, putting a flashlight behind the bowls of the filter in use is fairly easy. I also always take a glance at the vacuum gauge and expect that it will show problematic clogging ahead of the event by a rising vacuum. With respect to alarms, this subject may warrant a whole separate posting. Suffice it to say at this juncture that there are a lot of alarms on Alchemy. There are enough so I have a crib sheet, in descending order of importance, trying to differentiate alarm characteristics so that Ginger and I do not run around like Keystone Kops when one goes off (modern alarms are very hard to echo-locate—or is it my age). It seems to me unlikely that something catastrophic will occur (like would be the case with the alarm indicating a loss of oil pressure). Manual monitoring is likely to see water collecting in the bowl or an increase in vacuum and one can take necessary steps.
I certainly may have been fortunate over the years and hope I am not catching the notice of the fates in writing the above. In the statistically unlikely event of a catastrophically contaminated fuel source, and both tanks were filled, I will just flip the lever and change filters going through my supply of spares (usually more than 10) and limp in to a place of refuge where I can deal with the contamination. In any case, I am pretty sure I can protect the engine, a bottom line for me.
As always, I am interested in points I have not considered or errors.
My best, Dick Stevenson, s/v Alchemy

Marc Dacey

Dick, we seem to think largely along the same lines here when it comes to metal fuel tanks. My own solution is to extend my two metal 50 gallon diesel keel tanks by a 40 gallon keel beneath the engine itself. This will, in conjunction with a Filter Boss (yes, I bought one before I realized I could assemble something very similar for less cost) provide me with 140 gallons full fuel load, but with the capacity to isolate each tank. The plan is to have the 40 gallon tank as an oversized, post-filtered “day tank” that means I have a minimum of 30-40 gallons of “cleaned by me” fuel even if I fill Old Tanks One and Two with bug and dirt-filled garbage.

Which I would endeavour not to do, but one can’t always get one’s wishes.

As for your alarm-distinguishing problem, it should not be massively difficult to replace your various buzzers with the sort of circuitry that is found in “talking/singing birthday cards”, or “talking seatbelt alarms” in cars and the like. Or just the chips capable of holding a two or three word message, along with a small amplifier. Imagine instead of some random buzzer in D sharp, you heard your own voice saying “Fuel pump overpressure!” or “Bilge past six inches!” or the very useful “Exhaust temperature past 100C!”

If one did not wish to actually record specific messages, you could simply throw in random…but distinct…noises on pre-recorded chips, like birdsong means bilges, or fly buzzing means fuel, and so on. It’s the distinctiveness that is desirable. Buzzers tend to sound alike, because they all come from the same factory in China, I would imagine.

Combine the “talking alarm” with “The Clapper” for a shut-off, and you’ve got the basis for a marine products empire where the average customer’s age is already well past “I should’ve worn earplugs during that Alice Cooper concert”.

Like my idea for dim, five-second red LEDs that would be triggered by movement across the sill of companionways at night, or a 9V battery-powered, reed switch under-lid LED locker light, I do not see a strong objection in cost or complexity of a “talking alarm” to easily distinguish what part of the boat’s systems is complaining.

It only sounds like Star Trek. The actual electronics involved would not be beyond the average electronics hobbyist, which most cruisers already are.

R. Todd Smith

Thanks for the nice review of this product. I have seen, but not used it and it looks well designed and well built. I see it as a great tool for transferring fuel if you have multiple tanks and for switching filters if you have no other plumbing in that regards. Also, many folks struggle with bleeding fuel lines and filter boss seems to have that under control as well and the test function seems like a great feature.

However, If you have a single fuel tank, as many boats do, there are much simpler and economical ways to manage your fuel and filters. In fact, if you have a single fuel tank with the pickup properly located at the very bottom of the tank, with proper in line fuel filters leading up to the engine, you are about to discover a very big secret: you already own an excellent built in fuel polisher. That is because on many small diesels (and some larger ones) the fuel return, or bypass of excess diesel, exceeds your hourly fuel consumption by many times. On my 37 ft cutter with a three cylinder 29 hp Yanmar I use less than one GPH. However, when I take the fuel return hose and put into into portable fuel tank it will produce 4-5 gallons in a little over 30 minutes! Since I have a 35 gallon fuel tank I can expect to have that fuel cleaned many times as it passes through my water separator, racor and engine mounted filters! My experience bears this out. A simple manifold system is all I need for my parallel in line racor filters ( which ALL boats should have) and if I had multiple tanks a similar manifold could be applied there. Best of all I do not rely on any electricity other than to start the engine and the system is very simple, compact and easy to manage and bleed. It provides a $400 solution instead of $2k plus.

Now, I have a small engine and a small fuel supply, but even when cruising I rely on this with success.

If you have a large boat with lots of fuel the filtering rate and the other features of the filter boss can make good sense, but IMHO, it is serious cost overkill for the under 40 ft. crowd and I think that is an important distinction to make here even if it makes the Filter Boss folks unhappy. 🙂

Not to be a Luddite, but vacuum gauges are comforting perhaps, but really unnecessary. They also add another fault point as John rightly mentions. If you mount your parallel racor filters in an accessible way, you will always be able to reach them when the engine starts to choke on the clogged primary filter and switch the valves before the engine dies. The engine won’t normally die instantly but gives you minutes or even hours sometimes of warning with slight rpm fluctuations that are easily recognized. I have plenty of experience with this. Be alert and you will be in front of the problem. That vigilance will also help you stay tuned on for other engine issues that can/will develop. I you don’t believe my try it at the dock with the engine in neutral. Close the inlet valve to the active filter and see how long it takes the engine to sputter, then switch to the secondary filter and it will resume normal tempo. We actually practice this, but then we also practice “crazy” skills like sailing on and off of moorings and anchors and sailing into slips. We like to be able to comfortably use all alternatives to the engine if required.

S/V Twilight

John Harries

Hi Todd,

All good points, thank you. One place I would disagree. I don’t think that whether or not a polish system is required is anything to do with boat length. A 30 foot boat crippled by bad fuel is in just as much trouble as a 60 foot boat in the same situation.

Rather, the decision should be based on where you plan to cruise. The more remote the location, the more important having a polish system is. I have twice been in situations were the choice was dirty fuel, or no fuel. In these cases having a good polishing system saved the day.

I also can’t agree with using your engine as a polishing system, even though everything you say about fuel bypass rates is correct. Keep in mind that getting bad fuel in your engine can be VERY expensive (not to speak of a cruise ending event). Have you priced a new injector pump and new injectors for your Yanmar lately? Never mind the cost of replacement and finding someone competent to do the work. The point being that I want to clean the fuel before it goes anywhere near my engine.

Perhaps a smaller boat does not need a full system like Colin’s at over $2000, but filter boss have cheaper alternatives.

Marc Dacey

I recall mine costing $900, which is about two loads of fuel. It may be the simplest, least “automatic” version, but it has the two Racor 500s and the well-built pump, and like the non-electric Tank Tender system, I tend to favour “robust” over “comprehensive” or “electrified” in boat systems.

R. Todd Smith

Hi John,

Crippling fuel is certainly bad at any boat length, and with the fuel filter system I and others describe in this thread is that likely to be a real threat? Filter clogging might be a worry and I carry a large supply of filters for that. I understand your point about length, but my statement was related to the fact the shorter boats have lower fuel flow and lower fuel storage volumes so the problem is much more easily mitigated than with larger boat with multiple tanks and more fuel usage. More fuel equals potentially more volume of contaminants that clog more.

I have had plenty of fuel that looks like the back drop to a swamp creature horror movie and with proper pre filtering and a good filter system set up as previously described, all garnished with some biocide I have been just fine. I would be interested in learning about cases where this might not be adequate as I am always looking for ways to improve on these sorts of critical systems.

Further, if you cannot agree with using the filter system as a polishing system are you suggesting the polishing system works better? Is that a valid argument either way considering both methods use the same type of fuel filters? The way to ruin an injector is if the bad fuel gets past all the filters in the fuel line. ( As I understand it since it has never happened to me). If I have an adequate filter system that will not happen will it (?) and the returned fuel will be clean as well and by default as effective as a fuel polishing system, what with the three inline filters, plus pre filtering I might choose to give it when it goes into the tank. Dirty fuel has about as much chance of getting near my engine as Al Gore has of getting back together with Tipper. A fuel polishing system is essentially the same filters and will NOT add any additional level of security over time in to that configuration except that it might delay filter changes due to clogging. For that, I simply use all the money that I saved to buy more filters and change them more often.

That said, the effort of use might be easier for some and encourage better fuel quality management practices and at $900 instead to $2100 it might be easier to justify, BUT it still adds complexity and points of failure that must be taken into account like any other time/effort saving enhancement. Certainly I wouldn’t hesitate to recommend the FB for those that wish to go that way. I just see it as overkill and unnecessary complexity for many applications.

Anyway, a great dialogue in this thread.


Marc Dacey

Todd, I bought the Filter Boss prior to the decisions to repower with a Beta 60 (from a Westerbeke W-52 in need of a rebuild that would’ve cost 90% of a new Beta 60!) and prior to thinking that a disused 40 gallon keel tank would make a great day tank, which increases the complexity of my fuel manifold plumbing and your agreed-upon “points of failure”. Anyway, sometimes these things evolve organically and so does one’s thinking.

I am luckier than most in that I have a fully accessible engine bay and not a “doghouse” under the companionway. It makes addressing the space needs of “utilities” like the Filter Boss much easier.

There’s a lot of good stuff here, particularly about esoterica (to some, perhaps) of getting the sludge out of the tanks on a regular basis to lessen the burden on the filtering and polishing process, but in the context of the Filter Boss, I haven’t heard yet that it also traps, of course, water. I am choosing to reroute ALL tank vent line tund from the typical gunwhales or cabin sides to the pilothouse, either to a gooseneck or two on the roof or under the roof overhang. I got this idea from the same old book on North Sea trawlers where I first saw a transverse exhaust that dispenses with a siphon break (a particular bugbear of mine).

For the exhaust, see Dave Gerr’s drawing of what I mean here:

It strikes me that if you can run the vents higher, and T in a petcock for drainage at the bottom of the run, you stand a far better shot at keeping water out of the tanks completely without the use of problematic check valves. I would love to hear the thoughts of others on this, as of course keeping water AND dirt/goo/bugs out of the fuel is the job of the filters. Sorry, I can’t find an illustration of how I would want to run a vent line manifold…

John Harries

Hi Todd,

A lot of your points are valid and if you are comfortable, that’s great. We can argue the minutia here for a very long time. But in the end, I guess fuel polishing systems are kind of like over-sized anchors: the more miles and experience of voyaging to out of the way places the owner of a boat has, the more likely it is that they will have one.

Scott Flanders

We are from the dark side where clean fuel to the main is paramouont. With over 11,000 engine hours and a few miles we’ll pass along a little about fuel. The Racor ‘2 banger’ dual system with a vacuum gauge is a supurb system. We use 900 Racors even though 500’s would support the 50hp we use under way. The turbines of the 900’s don’t work because of the low fuel flow but the filter media is many times more. To specifically to answer Dick’s question, we change the filter elements at 4″ of vacuum. The filters fill much faster after 4″ so we change the elements proactively. We use 2 micron filters which is NOT recommended by Lugger (main engine). They recommend 10 micron. However, we are squeakers and run low rpm to stretch fuel. If we were running 500 Racors we would use 10 micron for sure. In marginal filter size applications, 2 micron filters will introduce air bubbles at high rpm and fuel starve the engine as well as trashing the injection pump.
Like others, we have found fuel around the world these days to be clean. We clean the tanks (2) once a year and actually Look into each tank. Over the years we have taken less than a thimble full of water and very little debris after thousands of gallons of fuel passing thru the tanks. The 10 micron polishing filter gets changed once a year and could probably go 3-4 years. Tank cleaning is the key.

We find with our first cousin sailors that cleaning and inspecting their fuel tanks are difficult in most production boats and therefore rely more on their filtering to keep things running. I would very much recommend in a new build or major refit case that accessable inspection plates be added.


John Harries

Hi Scott,

Great comment full of good wisdom that mirrors what we have learned.

I owe you a huge thank you. I have, over the years, had random air leaks in our Racor 500 fuel polish filter that have just about driven me banoodles.

Reading your comment made me realize what the problem is: Using 2 micron filters in a polish system with a powerful electric fuel pump is going to build a pulsing vacuum in the filter body that just about guarantees leaks…Duh! I will change to 10 micron.


Consider that if you go to 10 microns on polishing, you may find yourself needing to change the filter on the engine itself more often. Hopefully not a CAV-Lucas split case type as we had on our Perkins. And there is no vacuum gauge to let you know when this one is blocked, power just subtly goes south. There is a lot of crud between 2mics and 10.

When we lost main engine power from this secondary filter clog in ’96, we went back to 2mics in the Racor and just bled part of the pump flow flow back to the tank unpolished ($50 buck fix—2 tee’s some hose and a valve). The Racor and we were happy.

From our perspective polishing pumps should be sized to turn over a certain amount of fuel per unit time. We like complete tank turnover in a day when sailing in humid climes. We also find our solar panels can service the polishing demand and still keep us at 0Ah.

We have glass windows in the tops of our tanks and have just seen the first crud in 8 years thanks to a generally well regarded Georgia fuel stop. Now what we need is a miniature pool vacuum to go wander along the tank bottom ingesting the crud—I’m only sort of joking. Pool vacs are water turbine powered; a tank vac could be diesel turbine powered from polisher return flow. Their random movement has been shown to deliver 96% coverage in surprisingly little time. Clearly baffles and bizarre tank shapes would defeat such an idea. Still…

John Harries

Hi Chris,

Good point, but I’m not talking about the Racor that feeds our engine. That we will leave at 2 micron.

In our case we have a separate filter for polishing, and that’s the one I’m talking of changing over to 10 microns, which I think makes sense.

The pump we are using moves 40 gallons an hour, if memory serves. It is also a piston pump, so the vacuum it pulls oscillates. I’m pretty sure that fact combined with the 2 micron filter is why we have had trouble keeping air out of the Racor 500.


Ah! We use a high speed diaphragm pump and polish in parallel with fuel delivery.

Alan Teale

Another answer to Dick’s question; the manual for the Racor 500FG turbine filters suggests changing filters at “7 to 10 inches Hg, if power loss is noticed or annually, whichever comes first.” For those working in bars (now there’s a thought) seven to ten inches of Hg is of course ca. 0.3 bar. Alan

R. Todd Smith

I experienced the vacuum problem with the 2 micron filters when using only the fuel lift pump on the engine, but I didn’t want to go back to 10 micron. I installed a fuel pump upstream of all the filters. I have it wired to an on/off plunger switch at the engine panel, so if I start to get any clogging/starvation symptoms I just engage the auxiliary fuel pump and then change the filters at my earliest convenience. I has come through for me on a couple of occasions!

S/V Twilight

Douglas Pohl

Lots of good comments. From my 30 years of marine experience I choice Gulf Coast Filters for both diesel fuel and lube oil bypass filtering. The canisters are made of steel – never wears out or fails – lasts a lifetime, the filter elements are extremely cost effective at only ~$1.25 each (Bounty paper towel roll) and have performed well during the years of service on my yacht and oil field vessels I served on – I like seeing the actual filter medium up close when I change a GCF filter unlike the sealed expensive canister filter types – it only takes about five minutes to change a filter by opening the drain cock using nothing but my hands then unscrew the canister top and lift out the filter holder to remove the soiled filter then drop in a new clean filter add oil and re tightening to top – no tools are required.
My point is there are other good fuel/oil alternatives – what works for one might not be optimum for someone else – please checkout As always you can shop around for the best price since the trucking industry also uses GCF so you find them on many e-marketing/sales sites at deep discount prices.

No business relationship other than a satisfied customer.

John Harries

Hi Douglas,

Great tip, thank you. We looked at the Gulf Coast filters for our polish system some years ago, and would have really liked to use them for the reasons you state.

The problem was the size. At 22″ high, with the need for a further 20″ or so clearance above the filter required to change, totaling about 42 inches of vertical space required, we just could not fit them in anywhere.

And that’s in our 56′ boat with a walk in engine room. I suspect that most sailboats and many motor boats will have the same space problem, but for those who can fit them in, I think they are great.

Douglas Pohl

Remember GCF offer several sizes depending on horsepower requirements – space problem alternative is to use two smaller canisters plumbed accordingly. Sounds like you tried to fit the GCF large size when likely the standard size may have done the job. Size does matter. Keep the blog subjects coming – KUDOS!
Smooth seas,

John Harries

Hi Doug,

I could be wrong, but I’m pretty sure that the sizes I quoted are the smallest GCF filter.

Douglas Pohl

Just for the record there are three (3) GCF sized: Junior (no longer manufactured that I can find – available in the used-market), the Standard model 0-1 (~17.25″ tall see: and Large model 0-2 (~28.25″ tall see: Clear as mud? lol

John Harries

OK, now I’m really confused. The filters you linked to are listed as Bypass Oil Filters, not fuel filters. But assuming you can use them as fuel filters, the smallest one is still, as you say, 17″ high and the other one is even bigger than the one I linked to above.

Douglas Pohl

John, I’ll let you in on a little secret – how you plumb the canister determines if its a fuel filter or a bypass oil filter. The manufacturer OEMs all of the steel canisters with the same three ports in the bottom… the only difference is paint and the plumbing instructions…. fuel enters an off-center bottom port and flows through the filter media then overflows at the top down the center port stand-pipe this allows any water to settle at the bottom (fuel oil floats on water) and can be drained using the other bottom off-center peacock port in gross cases else is absorbed in the filter media for removal. The oil bypass canisters are user plumbed so oil enters at the bottom into the center standpipe port which overflows at the top of the canister draining down through the filter media and out of the canister off-center port. Even though a GCF says for fuel or says for oil you can interchange by correctly plumbing for the intended fuel or oil service. Hope that helps the confusion. Remember the filter media for both fuel or oil in a GCF is a Bounty paper towel roll costing about $1.25 vs $12-50.00 for the canister types. Of course GCF has their own filters with a knit sock over the meadia available for sale… lol

Douglas Pohl

Seems obvious but sometimes it just need to be said… if you are going to install auxillary filters then you need to consider a manifold – with the turn of the manifold valves your filters are inline for machinery use, turn the valves again and you can “polish” fuel from the day-tank or a specific fuel tank. When we are going to buy fuel I dip the tanks with water finding paste ( before bunkering – then again after filling the tanks with a different dip stick – any water in the tank shows as a bright red color. If the fuel vendor does not make amends I can turn a few fuel manifold valves, polish the fuel fuel, change the GCF for $1.25, re-dip the tank with a third dip-stick with water finding paste. Repeat as necessary until no detectable water is in that fuel tank. Underway I transfer fuel from a given fuel storage tank into a dedicated fuel day-tank and polish that day-tank fuel using the main engine injector fuel pump’s 3x excess fuel delivery from the return line into the day-tank. Don’t spend your money on buying gross amounts of filters – unlike buying a case of band-aids – solve the real problem with good engineering and smart technology – and of course some good user knowledge. Seems obvious but it needed to be said after reading additional comments.

Matt Marsh

If I am reading the Gulf Coast Filters manual correctly:
– They only make one size of fuel filter (the F-1), 22.5″ high.
– They only make one size of filter element (the 1 micron GCF-E1), 11.5″ high.
– Higher flow rates are achieved by plumbing several F-1s in parallel on a manifold.

That is, IMHO, a very smart way to do it from a manufacturing/distribution/logistics perspective.

The point about the height is a valid one, they are considerably taller than Racors and need a bit more clearance above.

scott flanders

John, the 2 micron filter media by itself creates air bubbles under a high flow. The extra pressure you mentioned causing leaks is secondary. We use a Walbro 12V fuel pump for polishing. The Walbro pump has a non serviceable bronze screen as a filter so in normal powerboat installations the pump pulls fuel thru the polishing filter rather than pushing. Having the pump on the downstream side of the filter guarantees a long service life. Using the fuel polishing system and by cleaning the tanks we have gone as long as 900 hours on a single main engine 2 micron filter. The exception was in Argentina where the fuel is so ‘dirty’, not from dirt but from refining, filters lasted 200 hours. I’m sure during your time there you experienced the same. It also cost a set of injectors.

The down and dirty way to clean tanks with small inspection plates or using the fuel sender port is by taking a wood dowel and ty wrapping a 1/2″ heavy wall hose connected to a Jabsco Water Puppy pump (12V or 24V as needed) using a 6303-0003 impeller (nitril) – not a more common 6303-0001 (neoprene that will swell in diesel). Using the dowel and hose as a sweep you clean the tank and filter the fuel back into the same opening using a Baja Filter or at the least a Racor 5 micron filter funnel. My wife helps as a 3d hand and it goes quite quickly. To take it a step farther, on the discharge hose after the first sweep to clean the downhill side you add a 3/8″ pipe to hose adapter on the discharge hose to pressurize the fuel and use that to agitate and clean the bottom of the tank. Let the mess settle and again run the fuel thru a filter.

Simple and very effective.

Colin Speedie

Hi All

many thanks to you all for so many excellent and informative comments. I apologise that I have been unable to reply until now due to being unable to access the internet.

Dick raised some very good points that I´d like to amplify – having either a drain valve, or dip sampling/pump out tube is an essential in my view, and also proper access hatches in tank tops to clean tanks out on a regular basis – we do ours every two years. But far too often this dirty, nasty job gets overlooked, hatches or not…

We have a manifold on the new fuel system to allow us to polish or inspect fuel in either tank, and although it´s not a system I´ve ever had on a boat before, Im finding it very useful – and also the ´vacuum test feature.

Thanks again for your comments.


Marc Dacey

I may be wrong in this, but I have a fragment of memory that says that a drain valve on a fuel tank is somehow illegal or “not ABYC spec” or “will bugger up one’s insurance”.

Certainly I’ve seen “lowest point in the tank” sumps with petcocks in my time, but I seem to recall they were somehow irregular.

Douglas Pohl

Marc – how about finding the ABYC or USCG inspection spec – good recommendations for consideration on an uninspected yacht – before shooting yourself in the foot with such a bold statement… lol

Marc Dacey

I *did* say I might be wrong…and I found my clarification:

According to this, what I pictured in my mind’s eye is in fact verboten for *gasoline* tanks, but is perfectly fine for diesel, or at least is not spoken of in the ABYC regs.

I own two sailboats, one with a gasoline engine (Atomic 4) and the one getting a repower currently…all diesel all the time. I have seen those sumps on both types of boats, and I must have come across the “no fuel sump” concept when I was replacing the fuel system on my Atomic 4 boat about eight years back.

So to find one on an old Alberg 30, say, would be a little irregular indeed, but not on a diesel-repowered one.

Scott Flanders

John, since this thread started we had our generator injector pump rebuilt. It went in because of leaking and they found the inside in poor shape with extensive scoring on the pistons. This is after fanatical care of the fuel, using a 500 Racor and 2 micron filters, plus changing the secondary filter. I wrote ‘Lugger Bob’ – Bob Senter, a trainer for Northern Lights/Lugger. Bob wrote an extensive reply that would be nice to share with your readers. Fuel is so important to all of us who cruise that informed information is priceless. If you would like Bob’s reply posted here let me know or if not just delete this posting. S.

doug siddens

Thank you Scott. I will enjoy reading Bob Senter’s thoughts.

Neil McCubbin

Boss filter looks great but is spendy
Like John, I think spin-on filter elements are an invention of the devil, and plan on getting rid of our Racor this year.
Being a Scotsman, I plan to buy a pair of Raco5 500 MA2 units and pipe up the parallel/easy switch system with a couple of ball valves, and incorporate a bleeding vent in the discharge side, above the filters, that runs back to the tanks. We already have an easy way to run to and from either of our two tanks, and a vacuum gauge visible from the helm.
Any comments welcome.

Marc Dacey

I am in the process, better late than never, of installing a KTI FilterBOSS. I have an existing FRAM C1191-catridged CAV fuel filter leading from my two keel tank diesel fuel manifold. Given that I am within all the height restrictions for the FilterBOSS, is there any reason I cannot keep this “prefilter” prior to the fuel reaching the FilterBOSS? Other than the two extra breaks in the fuel line, I mean? The FilterBOSS, of course, is usually a straight run from the tanks.

I have some known old fuel in my tanks, so the first job I want to do is to polish that fuel as well as I can, and a pile of C1191A cartridges willing to die in that cause. I’d rather abuse those first before the Racor 500s.

John Harries

Hi Marc,

I would strongly recommend that you get rid of the FRAM and then install new fuel lines with no breaks from the diesel tanks directly to the FilterBOSS. Many reasons:

  • Every filter you have in the system is another place for an air leak to develop.
  • If you ever do get an air leak, the more filters you have the more difficult it will be to troubleshoot, and air leaks are amoung the hardest things on a cruising boat to trouble shoot.
  • Every filter you have adds resistance that the lift pump must overcome.
  • The FRAM probably has no vac gauge, so you will have no idea that it’s becomming blocked, until the engine stops…on a lee shore…in a gale…at night.
  • You will have to carry and source two different filters…three with the on engine filter.

You know my mantra: simplify, simplify and when in doubt…simplify.

Marc Dacey

Yes, I do know your mantra, John, and I respect it, because you’ve neither drowned nor have you been bitten by bad practice (at least when you have, you’ve noted it and changed up your game). OK, I thought I would fly the “prefilter” kite and garner consensus. Thank you.

Interestingly, I asked this question elsewhere and was told “Racors are obsolete!” and was directed to read this:

Everyone’s got a drum to bang.

John Harries

Hi Marc,

Lots of good ideas in the article you link to. Having said that, you will be fine with Racor 500. I have been using them for 20 years with good results. The thing to understand is that with relatively small engines and tanks like yours and mine the Racor 500s have a ton of spare capacity.

Where problems start is when people try and run a 300 hp diesel through them that sucks 50 gallons an hour. (Most diesel engines pass a bunch more fuel than they use.)

Having said that, we carry 15 spare filters in case of a bad load of fuel. The most I have ever used to clean a load (290 gallons) was 7 and that was stuff we got in Greenland that was so dirty you could not see through a glass of it.

Marc Dacey

Reassuring words, John, that reinforce the idea that I don’t really need to use anything but the Filterboss’s Racors before my diesel’s on-block filters. I may opt for the Walbro in-line pump as well, although I doubt I need it that much given the height of draws I have. I too found the cited article interesting, but in terms of scale not necessarily applicable to us in the auxiliary diesel club.

John Harries

Hi Marc,

I’m not sure, but I believe that you can use the electric fuel pump on the FilterBOSS, both to fill the on-engine filter and to add pressure if the engine lift pump requires help (unlikely I think). If I’m right, you don’t need another electric fuel pump, particularly since they are notorious for air leaks.

Neil McCubbin

After my previous comment, I finally bought the Racor 500 twin filter set, instead of building my one
We have about 400 hours on it, with good success.
We have always changed fuel filters at about 10″ mercury vacuum. Our engine starts to misfire at about 17″
We installed an electric fuel pump on Beta Marine recommendation, but rarely run it.
We do use the pump to bleed the system. It is great to see the Racor fill up in seconds instead of hand pumping after a filter change. It would be rather slow to fill the Racors by hand pump.
We have a vacuum gauge on the Racor’s and a separate one (better quality) visible at the chart table. Both read same value.
With the electric pump, and the top-opening design, changing a filter is a fraction of the work of the old cartridge filter

John Harries

Great real world information, thanks Neil.

Bill Koppe

Hi Colin/John,
The Racor max units allow the use of either filter or both.
Thinking of using 10 and 2 micron filters in series in both a polishing set up and the engine filters. Any experience or thoughts on this?

John Harries

Hi Bill,

Two thoughts.

  • You definitely don’t want to use a 2 micron filter in either engine or polish feed. Simply too fine and will result in vacuum problems for the fuel pump. (I know this from personal experience!).
  • No, I would not put the two Racors in series, just more complication and air leak potential for no benefit. Better to use the second Racor as a hot spare.

Keep in mind that the on engine filter is designed to catch anything that gets through the Racor, so adding a lot of filtration before the fuel lift pump would be more likely to cause problems than solve them.

Marc Dacey

Agreed. I have a Filter Boss aboard and one working filter is enough. I monitor the vacuum gauge regularly and to date have not needed to install the Walbro inline pump I bought “in case”. In fact, I rarely switch on the FilterBoss’s own integral pump. I am quite happy with the unit, particularly as I am burning off elderly but evidently sound diesel fuel.