6.5 cooldown/warmup

[roosterjuicer]

after a long drive how long do you leave your motor idling before turning it off?

before driving how long do you leave your motor idling before hittin the road?

and, if i am goin somewhere for just a couple minutes (anything less than a half hour) i usually just leave my 6.5 running. does anyone else do that or is it not a good thing to do?

[Hubert]

Its all relative to how cold and how hard you are working the truck.

I try to idle a few seconds before going above idle. So the turbo has good oil flow before spooling up real boost. Then drive slow down the driveway and my road. As the trasmission and rear end are cold too. (read that once on here and it made sense)

I try and turn off the AC a few seconds maybe a minute on the road before getting to destination idle a few seconds before shutting down. Just to make sure turbo is going as slow as possible.

I really don't do anything too special. Mostly common sense if I just worked it hard I might idle longer or if it was real cold or been sitting a long time would warm up longer.

Lots of opinions on long idling vs shutting down. I don't have the occasions to let it idle too long. I probably won't idle over 5 or so minutes depending on frequency of stop/starts.

[MTTwister]

For cool-down - I idle it until the EGT's drop to about 300

[rjschoolcraft]

You should idle before shutdown until the exhaust temperature is below 300F to prevent oil coking in the turbocharger bearing. The time required for the EGT to drop varies based on ambient conditions and the how hard the engine has been working. It can vary from a few seconds to a couple of minutes.

[john8662]

Interesting, but I think an important detail has been left out here..

300F is the accepted cool down measurement, but is this pre or post turbo?

The reason I point this out is that I purchased an ISSPRO turbo temp monitor, and its specifically set to shut down at 300 post turbo with the thermocouple mounted in the downpipe.

Both of my thermocouples are mounted pre turbo.

Any comments?

[rjschoolcraft]

Pre-turbo 300F...

I make this statement based on the thermal capacity of the oil and observed heat soak characteristics. If others agree, that's cool, but it won't change my recommendation if they don't.

[charliepeterson]

I do 300* pre-turbo for shut down and as soon as the oil pressure comes up I'm on my way slowly so ALL the oils heat up. As soon as the thermostat opens for the first time you can drop the hammer if you wish.

[JoeyD]

I think after the turbo will give a better reading on acual turbo temp. I think the turbo cools down a little slower than the manifolds

[charliepeterson]

I like pre-turbo to protect the motor more than the turbo. After a good hard pull I'll let the engine idle down to 300* to protect the turbo before shut down. The other side of the pyrometer is where you could see an expensive meltdown if your not careful.

[DChristie]

For short stops - I shut it off and lock it up - an untrusting soul here. In Butte? That's not distrust, it's wisdom. My best friend from home went to "Tech" several years ago, He earned the nickname "hambone" after taking one in the teeth from a couple of the neighborhoodlums: Tex and Co-Tex, I think we called them. Nice hats. Stupid lookin' jeep though...

Once I have oil pressure I go. learned that from my Dad, 360,000 miles on 454 gasser.
For cool-down I ease around the last couple of turns and idle/coast to the driveway. I have know idea what the temps are.

DChristie

[Hansh]

I flew with a pilot who would wait 3 minutes before shutting down the aircraft engines. I think it was a Cessna 414 twin engine. He said this was to let the turbos cool down.

[rjschoolcraft]

Originally posted by HH:
I flew with a pilot who would wait 3 minutes before shutting down the aircraft engines. I think it was a Cessna 414 twin engine. He said this was to let the turbos cool down. On the Allison Model 250 that I used to be lead engineer on, we had a mandatory two minute cool down period before shut down...

[MTTwister]

DChristie - Yeah, we've got some real dandies up here. Then, for St Patties Day and Evel Kenivel week they feel the inner need to import more a--holes to tear up the town.

[JohnC]

Originally posted by HH:
I flew with a pilot who would wait 3 minutes before shutting down the aircraft engines. I think it was a Cessna 414 twin engine. He said this was to let the turbos cool down. Yeah, but they run 1650*F turbo inlet temps on air (read "oil") cooled engines...

[ogrice]

I have a pre luber external oiling system. It has a timing circuit for startup and shutdown. Very expensive, but its worth it for the piece of mind. I can only hope that it protects the engine like it says it does.

[Marty Lau]

Originally posted by ronniejoe:
</font><blockquote>quote:</font><hr />Originally posted by HH:
I flew with a pilot who would wait 3 minutes before shutting down the aircraft engines. I think it was a Cessna 414 twin engine. He said this was to let the turbos cool down. On the Allison Model 250 that I used to be lead engineer on, we had a mandatory two minute cool down period before shut down... </font>[/QUOTE]Ron;
Apples and bannanas here, C-414 has Continetial 6 cylinder Turbo charged Piston engines that produce 310 HP for take off IIRC. Allison is a Turbine engine is it not........

[rjschoolcraft]

It's not as apples and bananas as you think...

The Model 250 is a turbine engine, true. More generally, it is a turbomachine. The turbochargers on our trucks are turbomachines as well. The cool down requirement for our turbochargers is to prevent oil coking in the bearing housing from soak back. This is a significant, but not total, reason for the cool down requirement for the 250.

The other major reason for cooling down the 250 has to do with thermal stress gradients in the integrally cast, bladed turbine wheels. Max turbine inlet temperature on the 250 is around 1450-1475F (not far off from what our turbos see...). The blades will operate close to this temperature and the hub will operate somewhere near 1000F. Say we pull power (as you would to land) then immediately shut the engine down. The fuel is shut off, but inertia causes both spools to rotate breifly as they coast down. The compressor continues to pump air through the engine... much cooler air than before. Now the blades cool down rapidly to, say, under 500F. This creates a huge thermal gradient that causes rim cracks in the wheels. Hence, run at idle for two minutes to cool the entire wheel down evenly to prevent the gradients.

Since both are detrimentally impacted by oil coking, the requirement for both is really quite similar.