Engine "Cool down"

S

sjonesinfla

New Member
Mar 18, 2009
10
Naples, Florida
Boat Info
400 Sundancer 1999
Engines
Cat 3116 350's
I recently purchased a 1999 400DA with 3116's. A buddy (non-diesel owner) says I am supposed to let my engines idle for 5 minutes evertime I get back to my slip to allow them to cool down. I have never heard this before. Any truth to this?

I am a virgin diesel owner. Be kind!
 
No truth to this. Engines are already cool once you idle up to docks and back in your slip. You can idle if you and your neighbors like the smell of diesel fumes.
 
Well... I'm not sure about the 5 minutes after you get tied up (that would look kinda silly IMO) but, as my Cummins manual states, you need to let them run a minimum of 5 minutes after running at cruise. I don't think 5 minutes is long enough but by the time I idle into any port or anchorage, I've been idling much longer than 5 minutes and the engines have cooled down. You CAN NOT be cooking along at cruise and then shut the engines off immediately. This applies mostly when running out to your favorite fishing hole...

The important thing is to run your blowers anytime you are running at idle after the engines have heated up. You'll notice your blowers are plumbed to the top of the engine compartment and not the bottom like a gas engine. Note the location here in my engine room:

DSC_0062-3.jpg


They are there to remove heat... so at the end of a run when you you come off plane, you should turn on the blowers to extract the heat out of the engine room. There's no need to run the blowers before you start the engine... If you had gasoline or propane fumes in the engine room, they wouldn't remove them anyway.
 
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Thanks Gary. Did not know that. Good info about the blowers. I have to idle for the last 5-15min of every cruise to get to my slip.

Steve
 
What Gary said. The one thing you have to watch as Gary said is when you go out cruising to wherever and drop the hook let the engine cool down a bit with the blowers on.
Jack
 
The reason talk about letting a diesel cool down is that if the motor has a turbo, it's bearings are lubricated by a pressurized oil line from the engine. That turbo has been spinning at up to 20KRPM at cruise. To shut it down right after a run, you starve the bearings of oil as they cool down.
 
Just as a side note, after a long run, I usually let my blowers run for 30-45 minutes after I shut everything down.
 
Steve
Good question for us gas engine boys to read and learn.
I can't wait to get my first Diesel boat, to learn all the differences/systems.
Post that boat's info in your signature.
 
CapeCOD is 100 % right . Its all about the turbo.... I do as gary does and let the blowers run after I shut down.

Rob
 
With 3116's the turbos are the reason you need to let the engines cool down. Capecodcruiser is right, when the engines are under load, the turbos spool at 20,000+ rpms and the tolerances to just stay together at those speeds are really close. If you shut the engine down without allowing then to return to unloaded temperatures, expansion due to the heat generated at those speeds will damage the turbocharger.

But, this does not mean you must sit at the dock and idle for 5 minutes. The turbos will cool down if you run along at under 8-900 rpm. In fact, there is a school of thought that says the engines should be run at a fast dile before shutting down to ensure lubrication to the cylinder walls. Don't worry about looking for that in the Cat owners manual - its not in there.

I think Gary is right, for most of us going back home, to a fuel dock, into a marina usually entails some distance at idle....sometimes a lot. In my case during tourist season, its about 20 minutes, 10 minutes at other times. Chopping the throttles and shutting down at a fishing hole, dive spot, etc. is where you might run into a problem.
 
The other reason to run the blowers after shutting down is there is a lot of other stuff down in the engine room that is not going to be too happy sitting in 140 degree heat vs. 100 degree heat. Things like batteries, hoses, vacuflush systems, AC pumps, etc. are all down there. When I run the blowers after a long run, it feels like a hot hair dryer blowing out the sides of the boat.. Generally, I'll feel the air temp and when it cools down enough is when I turn off the blowers... which is usually 30-45 minutes.
 
The new issue of PMY discusses this in "Professor Diesel".
While I knew of the importance of a cool-down, what I didn't know is that it is recommended to race the engine in neutral several times before shutdown to clean the injectors.

"During slow speed operation in no-wake zones and other periods where low or idle speeds are called for , combustion chamber temperatures and pressures drop. This can result in incomplete combustion, which will allow carbon and soot to build up in the chambers and around the tips of the injectors and tops of the pistons. These deposits can adversely change the spray pattern of the injectors, causing misifirng and reduced combustion efficiency. Racing your engine in short bursts at the end of the cool down period helps remove these problematic deposits"...

Again, knew all about carbon build up from idling for extended periods. But I've always been under the assumption that occasionally (like a couple of times a day when trolling offshore) "burning" this stuff off was sufficient.

Any of you race your engines before shutdown?
 
Interesting......
I used to follow this practice with my VW GTI which had the 1.8T engine. The manual referenced cool down to prolong bearing life in the turbo.
 
fwebster said:
What? You don't have a digital thermometer in your engine room with a remote gauge on the bridge? Now that would be a cool mod!
Click to expand...

Heck Frank, lets take it one more step and tie the blowing into a thermostat that keeps the blow on until it drops down to 100+- degrees in the engine room:grin:

Sorry guys, hope you don't mind a small gas boater posting in this section, at least I did not say just trim up your drives when in shallow water.:smt024
 
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chuck1 said:
Heck Frank, lets take it one more step and tie the blowing into a thermostat that keeps the blow on until it drops down to 100+- degrees in the engine room:grin:

Sorry guys, hope you don't mind a small gas boater posting in this section, at least I did not say just trim up your drives when in shallow water.:smt024
Click to expand...

Why not just add AC with a thermostat:grin:
 
Used to let the Turbo's cool on a JD hillside combine after we were done cutting as well. It wasn't enclosed like a bilge engine compartment, but it was recommended for the same reasons stated above, to lube the turbo's. The manual there stated a couple minutes at idle would suffice. Usually by the time we unloaded and found a spot to park we had idled down for a period of time longer than suggested. I let my Duramax idle after towing as well.
 
I do in my two volvopenta and yanmar and cat both of them common rail turbo diesel; when lowering the rpm to arriving or anchoring open the blower(s) run under 2000 rpm to stop the turbo then leave engine to cool down 2 3 minutes to stoping the turbo's pals with lubricating meanwhile the engine oil is comesdown to the crankcase so after 3 minutes stop the engines but let the blowers run 15 minutes to discgarge the hot air from the engine room.
 
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