I have long known that the oft-accepted wisdom that an engine should be warmed up at idle before loading it was wrong. In fact, we should load it almost immediately by going into gear and then slowly increase revs as the engine warms up.
Warm-Up
A few engine manuals share a not-to-exceed power setting before the engine has reached temperature, but most don’t, so this is what I do with our Yanmar 3YM30 that tops out at 3200 rpm WOT1:
Hi John,
It is fun and stimulating to have your essays on what are, for most of us, procedures we have not thought about nor considered in any depth in decades.
Thanks, Dick
Hi Dick,
Thanks for the kind words. I agree, half the fun of running this business, and continuing to be a boat owner, is the new stuff I learn.
Is running the engine at the slip in neutral at normal cruising RPM (for us 2,400-2,800 rpm) bad for the engine and/or Sail drive?
I do that periodically if we aren’t using the boat for say 4-6 weeks. I’ll start it, let it run for 30-60 seconds and then slowly throttle up and let it stay there until it reaches normal operating temperature (about 160-170 degrees) and then shut down.
Our engine is a Yanmar 3YM20.
Hi Bob,
Yes, bad for the engine. In fact about as bad as it gets for wear.
If you read Eric’s full comment he addresses that. What some do, and is advised in the Perkins manual, if the engine has not been run for more than say two weeks is keep your finger on the stop button and turn the engine for 30 seconds before taking your finger off and letting it start. This is claimed to pre-lube an engine that has been sitting for a while. That said, the danger if you do this too long is filling the lift and flooding the engine, so if you want to do this, as we did on the McCurdy and Rhodes, install drain valve in the lift you open when doing this.
All that said, I would probably not bother with any of that and just stop running the engine in neutral like that and just start it when you need it and will load it while being underway.
Hi Bob,
My SOP when I wish to give the engine a little exercise (such as warming the gearbox and engine to change oil etc.), is to run it in forward gear in the slip (and generally a bit in reverse) and simulate the regimen that John suggests for getting up the operating temperature. One caveat I have heard about is that there are some scoop-type raw water intake covers which do not allow adequate flow as the boat is not moving thereby interfering with water being “scooped” into the engine.
I use the stop button to induce oil distribution, but only at the first start after a winter of storage and not during the season even if it has been a few weeks between starts: The stop button is hard to get to and requires 2 people to start the engine. Casual research has supported this stance: perhaps I will review this decision.
My best, Dick Stevenson, s/v Alchemy
Hi Dick,
I have done the same when alongside for long periods and do the same on the stop button hack.
Hi Dick,
My water intake is on the SD25 Sail Drive so I think it’s fine. I always made the assumption that it was OK to run the engine at normal cruising RPM but not in gear because I see (and hear) diesel trucks with their engines idling all the time. I’ve run the engine at normal cruising speed at the dock in gear before so it’s not a problem.
This brings up another question. What if you are at anchor at night and for whatever reason, your batteries need charging. Most people would start the engine and probably run it for 30-45 minutes out of gear and apparently be blissfully ignorant they are putting more wear on the engine. Would you consider running it in reverse (a well set anchor should hold) to put it under proper load?
Very interesting conversation!
Cheers,
Bob Hodges
Hi Bob,
I would not bother with putting the engine in reverse, but rather make sure the alternator was big enough to both get the job done quickly and load the engine a bit, without being too big. Eric’s articles and mine on installation will help with that.
Don’t do that.
Most of the wear on the engine happens in the first 60 seconds after being started from cold. As far as total engine longevity is concerned, the number of cold-hot-cold cycles is just as important as total hours run…. and consecutive hours sitting unused doesn’t matter very much at all.
Diesels really do not like being run regularly at high rpm without load. I only ever do this for the purposes of tracking down a weird vibration / noise / etc. Normal warm-up procedure is usually to idle in neutral for a minute or two, until you’re sure that fuel & cooling water flows are good and that nothing seems to be broken, and then to put it in gear and go. Let it warm up under load, and wait until it’s warmed up that way before using higher power settings – just as specified in the article above.
If you do not actually *need* to run the engine, just leave it off. Follow the engine manual’s long-term storage procedure if it’s going to be abandoned for an extended period (months or more).
No intake grate should ever make proper cooling flow dependent on boat motion. If it does, that needs to be fixed. Engines must be able to get all the cooling water they need at any RPM in any state of boat motion, forward or reverse.
Good stuff. It is worth noticing that running at light loads and temps can result not only in wear, but also in glazing of the cylinders, which in turns leads to low compression, oil consumption, smoke, etc. Bad glazing requires tearing down and honing the cylinders. The suggestion of running hard from time to time can address that and seems a very good one.
Hi Stefano,
Absolutely: https://www.morganscloud.com/2016/04/12/how-to-stop-killing-your-engine-with-kindness/
Obviously you are correct from a wear perspective. I only let the engine run for a few minutes before heading out, that spent untying lines and removing sail covers, which don’t take me long. But I think for the occasional sailor, most engines die of corrosion and disuse. Perhaps they have not run the engine for weeks or months.
What I have learned is that probably 90% of my serious running problems happened very shortly after start-up, and they are typically fuel related. A fitting or filter leaking air. Something stirred up that fouled a filter or clogged a carb jet. In several (feels like most) cases they waited just long enough to catch me between rock jetties in a sharp cross wind or some equally dire circumstance. No worries; I’m good ant anchoring very quickly or contingency maneuvering, but still unpleasant and memorable. Sure, some were the result of an avoidable maintenance errors … but they happened. And some were just “shit happens” and not predictable or preventable. A freak failure.
I might modify the advice to include running the engine at dock for a good 15 minutes after any significant maintenance or long period of layup. You can run it under load; the few hundred pounds of thrust should be no strain for your dock tie-up. In fact, it is a normal thing for me to run the engine a few times each winter, when there is too much ice to go out. I run it under load, for long enough to warm up and to clear the fuel between the tank and the engine. It really seems to help with reliability. I only allow the engine to run without load for long enough for it to warm up enough to take load (gasoline engines, typically), which should only be less than one minute.
You don’t warm up a car. Well, you did a little back in the day (50 years ago when I was learning to drive) when it was below ~ 15F at night, because they didn’t really run right for the first few minutes and you needed to get the ice off the windshield anyway. Old tech. But even in that example, it really only took about a minute until the car was driveable and should be under load.
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I understand the mantra about loading diesels for optimal life. But my expereince with diesel trucks with high idle time suggests it’s not as deadly as all that. Dump trucks. Buses. Trash trucks. Much farm and construction equipment, such as cranes. High idle time really is a normal thing and it is in the design basis. It’s good to inform people, but we don’t need to scare them. Warming up at idle does not help, but idle time isn’t scary either, within reason.
Hi Drew,
Good point about an engine fail just after leaving the wharf, and a good solution.
Agreed. Most sailboat setups havebat least 5 to 8 minutes worth of idle fuel between the big filter and the injector pump. If you’ve opened the fuel system in any way, that’s how long it’ll take to be sure you don’t have an air bubble that failed to bleed and will interrupt power at just the wrong moment.
OK, I’ll admit to this one simple bungle.
I replaced both gas filters (twin Yamahas). Routine. I started the engines, up ran until I was right between the rock jetties in a gusty 25-30 knot cross wind, and one died. No worries, I can sort that out once I am in the clear. 30 seconds later the engine other died. Since the wind was slightly ahead, the odds of pulling out a sail and nearly beating out aren’t encouraging. I have momentum, so I spun into the wind, coasted to near the windward jetty, walked forward and dropped the hook just as the boat stopped (always have an anchor ready to go). I let out scope and snubbed it well clear of the other jetty. Yes, I’m anchored across the channel, but this is an emergency and no one else is out in this weather. I now have time to calmly sort it out.
I forgot to open the fuel valves. A minute later both engines were running and I was raising anchor.
Hi Drew and all,
I do not think there is any entity that humbles me more than my boat. Or, to put it another way: if I am ever in danger of getting too full of myself: spend some time with my boat.
My best, Dick Stevenson, s/v Alchemy
Hi Drew,
We can all make that hind of mistake, I know I have, good on you for sharing it and reminding us all of the importance of having an anchor ready to go.
Hello,
We have a private mooring with three underwater walls around the boat. Putting the boat in gear for warming up is not recommended in our specific setup not for the engine but for the good health of the joints and foundations of the walls.
This was confirmed by the underwater construction company that does the maintenance.
Hi Denis,
That makes sense. Im that case I would just get going after starting the engine, except in cases where I had worked on something like changing a fuel filter.
Hi John
What are your thoughts on warming up a genset engine with a fixed rpm as soon as it starts. Should it be loaded straight away or let warm up before applying a load.
Cheers
Cameron
Gensets are designed to be loaded as soon as the rpm stabilizes. If they have automated controllers, then the process of start – synchronize – connect rarely takes more than a minute, even on huge ones. With manual control, I’d start it, let it come up to 1800 / 3600 rpm (or 1500 / 3000 for Europeans), make sure it’s pumping cooling water, and then throw the breaker.
Hi Cameron,
I would agree with Matt, but might not put all the loads on immediately and so ramp up a bit as Eric suggests for engines.
Hi Cameron,
Most gensets that I know of are 1500/1800rpm units which isn’t too bad to go to after a minute or so at idle. Then as John suggests, you can slowly increase the load by turning on more chargers (some will let you program to ramp over a few minutes which works well too). I have seen some which allow a high idle for a little warmup before loading and that is probably a little better but I am not sure how many users would be able to tell the difference. Looking at what engine companies do for programming high idles is really instructive. The primary purpose of these is to warm the engine up more quickly and then keep it warm but sometimes it doubles to power things like PTO’s. You usually see something like 1200-1500rpm and if the engine has a variable geometry turbo, they close the turbo to put backpressure on the engine which is what makes the whooshing noise. Once the engine is up to temp, some of these programs then drop the engine speed a bit or open the turbo a bit to save on fuel but keep the engine at temp.
One thing that can be confusing is a lot of gensets are rated for how quickly they can take full load. This rating exists because they are being used as a backup and so being able to switchover and go to full load quickly matters to keep from browning out whatever it is powering. However, this type of operation is far from ideal from an engine longevity standpoint. Everything is a trade-off and those use cases usually don’t do a ton of hours but have to do very rapid loading. For most cruising boats, the generator gets started to charge batteries which don’t have this immediate need so ideally we would ramp the load over several minutes.
Eric
Some say running the engine WOT (under load) every once in a while is good for it, thoughts? If so how often and long?
Hi Richard,
That’s correct, but more to know: https://www.morganscloud.com/2016/04/17/how-to-select-the-best-power-and-propeller-settings-for-your-engine/