Is your engine cool?

[Dick Carey]

Engine Cool Down

I always cool down the engine after running it by running at idle for 5 minutes before shutdown.Dick CareyS/V Puffin

 

[Vic]

And for 15 years I've done it wrong?

on my Yanmar 2 GM ... I just shut it down after about 30 seconds of idle . I wonder if I have hurt it's life much ... maybe I won't get another 15 years out of it?There must be people out there that still start up their cars and run them for a five minutes before they put the gear in drive.

 

[Ralph Johnstone]

Vic of Newport .....................

I'd be surprised if you get much more than thirty to forty years out of your engine treating it like that. ~Best Regards,s/v Island Hunter

 

[Tim Leighton]

"HEAT SOAKBACK"

I became very familiar with the term "heat soakback" in my days as a Navy operational flight test pilot on a new version of a carrier based aircraft. All engines, regardless of type, when shutdown, actually experience a rise in temperature for a period of time ("heat soakback"). You may not see that rise depending on where your temp probe is. On the airplane I mentioned, the heat rise was on the order of 20% for about 5-7 minutes! The whole idea is to limit the amount of temperature rise. The amount of rise depends on the latent heat of the engine at shutdown (OK, for those of us who are journalism majors...how fast you were running the thing!), internal makeup of the engine, and external factors such as compartment size and outside air temperature. Almost all the previous posts were exactly right about the cooldown cycle but one thing not mentioned is the "crystallization" of fuel at the tip of the fuel nozzles. When a "hot" engine is shutdown and subsequently heats up, if the internal temperature reaches a specific point, the minute amoount of fuel left on the end of the fuel injectors crystalizes. Over time that leads to blockage of the nozzles, and expensive repairs. That is one reason why Yanmar, and most other engine makers, recommends a 5 minute cool down cycle.  I hope this helps answer Dave's question as to why a cooldown cycle is important.Tim (S/V "TIDE")PS: The Navy solved the problem the same way we do...run the engine at a lower "RPM" for a couple minutes before shutting down!

 

[Douglas]

Bottom line

The bottom line I suppose is that it is your engine. I choose to shut the engine down the way Yanmar recommends. After I dock, the engine is idling, I secure all my dock lines, put the life jackets away, get the sail cover, pedestle cover and winch covers ready and by then five minute or so have past. Am I extending the life of the engine? I don't know - I know it can't hurt it. Heck, I choose not to smoke - if I did smoke would I die from a smoking related death? Don't know but don't see the need to take the chance.Dougs/v BrendaGail

 

[Paul Akers]

Well said, Doug

A 5 minute investment will pay back under ANY circumstances.

 

[Frank Arndorfer]

Agree with Tim....and Dave.

I agree with both Tim and Dave. My experience is that these Yanmars (and most any internal combustion engine) will "heat-soak" when quickly shut down. My 3GM will do this....so why not let it cool with water circulation while idling.????Dave's idea about doing your tying up checklist while the engine is still idling sounds worthwhile. What's to lose except a half cup of fuel.?????

 

[John Eastin]

Of Course

Mine is a two stroke outboard so I normally just let it idle, pull the gas hose off it and let it run out of gas. Not sure why but someone told me it was a good idea so years ago.

 

[SailboatOwners.com]

Final results

Final results for the Quick Quiz ending 8/27/2001:Do you idle your engine to cool it down after running?48% 2-10 minutes24% No24% 2 minutes or less03% 10 minutes or more

 

[george lakesiii]

Start /Stop reasons

Having been a diesel mechanic and driven semi's, I submit the following.Diesels are significantly different from most gas engines in that they have fuel injectors that need to be kept clean. They operate at high fuel pressures and the engines have high compression ratios in order to to ignite the fuel without a spark plug. Remember if you compress a gas it gets hot. This leads to combustion at a cold start with the requirement on occasion for glow plugs to give enough heat so that the engine doesn't get so overloaded with fuel before start, that the rings get washed out with fuel that gets past the rings and dilutes the oil with raw fuel hindering the oils ability to lubricate. If this is done the potential for bearing wear increases dramatically. Approx. 90% of wear occurs during start up. Once started and the oil pressure rises it is good to run the engine slightly above idle from 900-1400 rpm depending on the temp to get complete combustion. If your engine instruments included a pyrometer (used for indicating exhaust gas temp) you would be able to see the bennefits of idle down and start up. At start up the exhaust smells of incomplete combustion and will be of a white/blue color until warmed up. It is good for an engine both diesel and gas to be brought up to peak operating temp when run to get rid of any moisture in the engine oil. Now for shut down. If you had a pyrometer, depending on the location of the probe/sensor you would see on a turbo charged engine (most semis) that the exhaust gas temp could be over 1200 degrees farenheit. This tends to help oxidize the oil and a reason you need to change it annually if you put 50hrs on it or only 5 hrs. This is the reason you see semi's idle down. As mentioned in another post, the heat soak is phenomenal. The turbos are actually oil and air cooled. Another reason many semi's have oil temp as well as pressure guages. I have seen a turbo at 1200 F and after stopping you can have the temp down to 600F or less in one minute if you have the engine run at 1400 rpm under a no load condition. The engine will become an air pump drawing enough air through but using little fuel. Fuel creates the heat. The engine will not use the same amount of fuel at 1400 no load as it will at 1400 in a loaded condition. This is the reason I follow the mfg. reccommendation of running the engine at 3000-3400 rpm for one minute prior to shut down. Bring the rpm down slowly or incrementally to idle after cleaning out the unburned fuel. The engine only uses what it needs, that is why there is a fuel return line. BTW most diesels have an optimum operating rpm of where the horse power and torque curves cross. By running the engine at the higher rpm, the water flow should be at an optimum flow to remove heat, as little is being created under a no load condition. This is just a good way to remove heat from the engine and the turbo. If you were to shut down without sufficient cooling, the hot turbo will heat soak the oil to the turbo. This can cause cokeing and creates small hard pieces that circulate in your engine. Not as big as sand but will wear on your engine just the same. When you see a truck on the highway take note of the color of the exhaust. At cruise you should see just heat waves indicating proper combustion. If it makes constant black smoke from a turbocharged engine the injectors are to big or the rail pressure to high. Boats are somewhat of an anomally, as many are not turbocharged and operate at a compromise with mechanical injection that needs to get proper throttle response and cruise. Computers will be able to change alot of this in the future.

 

[Charles]

A4 Start And Stop

I let my A4 warm up while we prepare to leave the slip. And when we get back I let it idle while we tie up. I also reduce to idle while raising and lowering the sails.