Leaving Diesel Run

I'm a retired truckdriver that drove mostly CAT engines and I would let them idle while doing my log book then shut the engine off.

Cloud Dancer wrote:
Does it hurt anything to always let the turbo(ed) engine run at idle for 5 minutes before shut down?
.

Yes. Environment. (not to mention owner pocket)
In California they actually made a law forbidding idling.
Wolfe is making good point about thinking.
I was hauling heavy with my manual diesel pickup in the past, but when I was coming to rest area, I would switch to N about 1/2 mile before exit. By the time I rolled down to stop the engine already had couple of minutes of low rpm with good air flow.
Not all turbos require cooling.
We drive turbodiesels in Mercedes for over 20 years and cooling them down was never an issue.
You can also buy a module that will keep engine running for few minutes after removing key from ignition.
My son bought gasoline, sport car Mitsubishi where PO installed such module to prolong turbo on it. Sure made some strange looks when you close the door and walk away from car with engine running.
Than some engines do have electric coolant circulation pump that will even engine hot spots for few minutes after shut down.

Cloud Dancer wrote:
Does it hurt anything to always let the turbo(ed) engine run at idle for 5 minutes before shut down?
BTW the diesel engine that powers my ONAN generator does not have a turbo. That one I simply shut down right after it's been running at normal speed.

If you read your owners manual it will tell you to let it idle under no load for 3-5 minuets before shutting down.
Bill

want-a-be wrote:
Should you leave a diesel run for awhile before shutting down, if so how long should you leave it run? I have heard you should leave it run to let the turbo cool down but what if you do not have a turbo?
Thanks for all comments

Help me understand your question. What diesel engine are you talking about? Your coach has a turbo on the engine and you should let it cool down as others have commented. Now your generator doesn't have a turbo. You should follow the instructions in the owners manual and let it run for a while with no load to cool down. My book says 3-5 min with no load.
On my coach I liked to get my EGT temps under 450degrees.Most of the time just getting into a camp ground is enough time. If stopping at a rest stop or for fuel I may have to wait 3-7 min depending on ambient temperatures.
Bill

johntank wrote:

Matt_Colie wrote:
As an Ex-engineer that did a lot of automotive, I say that you are well advised to let any turbocharged engine cool a little while before shutting it down. By let it cool, I mean let it run at something less than highway load for about a minute. That is all it takes for the system to get a lot of the heat out of the supercharger body.

I think this is a good answer for most, now this is my thinking by the time one pulls of the highway and gets to a fuel station or campground this should be enough time for a cool down.
This goes along with what is in Mat's quote. JMHO

I will usually air level before shutting down the engine. That's more than enough time for the turbo to cool down.

Does it hurt anything to always let the turbo(ed) engine run at idle for 5 minutes before shut down?
BTW the diesel engine that powers my ONAN generator does not have a turbo. That one I simply shut down right after it's been running at normal speed.

As an Engineer and former diesel mechanic, I disagree with people who said that you don't need to let them run after a hard pull. Diesel combustion chambers can reach very high temperatures under load, even without a turbo. If you don't run the engine for a few minutes after a hard pull, the engine temperature doesn't equalize and some parts will cool significantly faster than others. You will end up with warped heads and blown head gaskets. You will find that most engine manufacturers recommend a short cool down period before shutting the engine off.

Many new diesels have Exhaust Gas Recirculation (EGR) coolers that use engine coolant to cool exhaust gases before injecting the cooled gas back into the cylinders. Under load, the EGR coolers can get up to 1400 degrees and coolant that's in the EGR cooler can actually break down and precipitate into solid particles. The solids clog the oil cooler (which uses engine coolant to cool the oil) and the EGR cooler. This causes early failure and can be very expensive.

Letting the engine run for a couple of minutes is cheap insurance to prevent an expensive repair bill.

As some posters have mentioned, the best source for advice on this is the manufacturer's manual.

Executive wrote:
Simple answer to OP's question...he does NOT have a turbo, but thanks to all the engineers that responded relative to turbos....:h...anyway, new NON TURBO diesel engines do not need a cool down period.....Dennis

And you know this how?

wolfe10 wrote:

DanTheRVMan wrote:

wolfe10 wrote:
Interesting-- been a very long time since I have seen a normally aspirated diesel on the road. What do you have???

And as already answered, with a turbo diesel the answer is "IT DEPENDS".

If you just climbed a 5 mile 6% grade and pull over in a scenic overlook, yes 3-4 minutes would be proper.

But, if you got off the highway and drove at low speed to the CG and checked in, the instant you get to your site turn it off.

As with most things, a little common sense goes a long way.

Different way to address the same issue is to cool the engine below 180F. Times will vary a lot depending on hills, ambient temp, etc.

BTW, Camp Frieghtliner suggested <180F

Dan,

This one confuses me. The thermostat(s) SHOULD control engine coolant temperature. So, unless the temperature is above thermostatic control (i.e. thermostat(s) wide open and some other part of the cooling system is limiting cooling capacity) the temperature should never drop below thermostat set temperature.

Said another way, you should be able to idle for a long time/way longer than you need, and if you have a 190 degree thermostat for example, coolant temperature will remain above 180 degrees.

If what they meant was to idle until temperature returns to thermostatically controlled temperature-- that makes perfect sense. So, if the thermostat is 180, then perfect answer.

Brett,

Your answer is more detailed and clearer than Camp Friegthliner.

I guess since everyone in the class owned a Frieghtliner they just stated the thermostat setting of 180F. Class is so so imo. Long and boring when selling Frieghtliner (most of the class) and then rush thru technical info:S

DanTheRVMan wrote:

wolfe10 wrote:
Interesting-- been a very long time since I have seen a normally aspirated diesel on the road. What do you have???

And as already answered, with a turbo diesel the answer is "IT DEPENDS".

If you just climbed a 5 mile 6% grade and pull over in a scenic overlook, yes 3-4 minutes would be proper.

But, if you got off the highway and drove at low speed to the CG and checked in, the instant you get to your site turn it off.

As with most things, a little common sense goes a long way.

Different way to address the same issue is to cool the engine below 180F. Times will vary a lot depending on hills, ambient temp, etc.

BTW, Camp Frieghtliner suggested <180F

Dan,

This one confuses me. The thermostat(s) SHOULD control engine coolant temperature. So, unless the temperature is above thermostatic control (i.e. thermostat(s) wide open and some other part of the cooling system is limiting cooling capacity) the temperature should never drop below thermostat set temperature.

Said another way, you should be able to idle for a long time/way longer than you need, and if you have a 190 degree thermostat for example, coolant temperature will remain above 180 degrees.

If what they meant was to idle until temperature returns to thermostatically controlled temperature-- that makes perfect sense. So, if the thermostat is 180, then perfect answer.