Talking to a Duramax owner the other day and he says he plays heck getting the wife to cool the motor down to a certain temp before shutting the truck off. I know I know, what the heck is the wife doing driving the truck anyway. He says she loves the thing and will take it when ever she can.

I've not seen anyone here talk about a cool down temp but wondering if any of you do something similar?

Thanks,

 

Nope. When I get where I am going I turn off the truck.
My wife does the same thing. (she has her own truck..)

 

I have a BD cool down timer on Tom. If I'm towing I'll let it idle til the EGT drop below 325. Most of the time just running around town, it'll be below that by the time I find a parking place. It's mostly about cooling the turbo bushings/bearings.

Barney

 

What he said, I have been told by my mechanic if I want to help my turbo live a long a happy life i should let it cool down to under 400 degrees before I shut it off. It is even more important if you are towing or have tunes on your truck. Since all of my trucks have tunes and only one has gauges I let them all sit for a little bit if I have been running them hard or towing. I can't say it has helped and can't say it would hurt anything at all, as you don't want a smoking hot turbo sitting there cooking/coking the oil in the turbo after you shut it down. I plan on having gauges in every vehicle so I can watch them. Like he said before very rarely do I have to sit more then 30 seconds of the turbo to cool down before I shut it off on the truck that has gauges.

 

I think my EGTs are below 400 before I even get off the highway. By the time I get parked the gauge usually reads around 300 degrees so that is why I've never been concerned about letting anything cool down.

When our fleet trucks return to the yard, the guys just shut them down. We gripe at them if they leave the engine running after they are parked. California has a law against excessive diesel idling but I don't think they are enforcing it yet...

 

Thanks guys. I figured as much but wanted your advice. Watching mine since he said something and after a very short Idle time its at about 300.

One less thing to worry about

 

Where is your pyrometer probe? On my cummins it is after the turbo in the down pipe. It usually runs around 250-300 just idling. I usually run that truck pretty hard at times. So for it to have 278K miles, the original turbo, injectors, etc is pretty good, esp. when I have seen 45-55psi boost on that truck fairly often since it was studded.
If your truck is down that low after cruising on the freeway I doubt you have much to worry about.
I am glad AZ doesn't have those stupid idling laws... just today I pulled off in a park up in N Scottsdale and took a nap for an hour for lunch... I had to turn up the AC as it was freezing me out.... I could not keep my eyes open today... There are some days I kick on the high idle to super cool it down.

 

On my red truck, the sensor is pre-turbo. I watched it on the way home out of curiousity and the EGT temp was 350 before I came to a stop while exiting at Superstition Springs. It hung around 400-450 while driving on the surface streets and dropped to 325ish within seconds of placing the shifter in Park. By the time I gathered my cell phone and briefcase the EGTs were a hair above 300.

 

Mine takes a little longer to cool down during these Texas summers. With the additional heat given off the condenser, I sometimes have to turn the a/c off to allow the EGTs to drop quickly.

 

Now you guys have me curious....it was 107 today and my A/C hasn't been turned off since early June. I think I will drive a different truck tomorrow and see if the EGTs are warmer.

 

So I drove the 450 today and paid attention to the EGT gauge a bit more. Like my pickup, the EGTs drop below 400 degrees by the time I exited the freeway (gauge read around 375-380 ish...). However, unlike my pickup it didn't fall any lower than that when I pulled into my parking spot. I had to let it idle for almost a minute and a half until the gauge read about 325. Another minute of idling got it down just below 300 degrees. On this truck, the thermocouple is post turbo in the short elbow housing between the turbine outlet and Banks Brake. It's also a Banks gauge.

I expect there to be some variance between gauges, even of the same brand so the exact numbers are arbitrary at best. I wonder why the 450 took so long to cool down even after it was parked? I have one more truck to try. I'll drive that one tomorrow and see how fast it cools down....

 

I have been letting my truck cool down to 300* since the day I installed my gauges. I've been told that 400* is ok if your in a hurry to shut it down 300* or less is better. My wife also does this when she drives my truck. Timmyboy if you're reading this you know how that turbo was treated.
After I installed my van turbo I went into a play bog for a little while... You couldn't tell the truck was white when I pulled out. My egts at an idle stayed steady at 750* so we can all imagine what they were at while I was running it HARD. I let it run while I went and walked around came back about 5 mins later and they were still too hot after about 10 mins total they were down to 300* on the gauge and I shut her off.

 

So I've been driving to various job sites today and have watched my EGT gauge a bit more. The Banks DynaFact EGT gauge has a very slow reaction time. By contrast, my ISSPRO gauge moves up and down very quickly so it seems more 'real time'. The Banks gauge has some sort of delay which causes the needle to react slowly. I peeked at their website and they advertise some sort of correction factor built into their gauge that compensates for ambient temperature. Not sure what that is about....


One of our fleet mechanics was delivering a truck today so I took the opportunity to ask his opinions. He feels it's good practice for the EGTs to be 400 degrees or less before the engine shuts down. So by default that is what we are doing anyway (even without the benefit of having a gauge installed).

I later talked to a UL inspector about a completely different issue and the subject of thermocouples came up. He said that K type units deviate at it's "Curie Point" (I had to look that one up...). That point is around 350 degrees (according to Wikipedia). As far as I know, all manufacturers use K type thermocouples for EGT gauges so temps of 350 degrees or less should be taken with a grain of salt. Most of the brands that I looked up today advertise 1-2% accuracy at max temp but they don't say anything about accuracy at the cooler end of the spectrum.

 

Very interesting. Good info to know.

 

did a rant couple of years back about EGT gauges and thermocouples in this forum. the slower reacting ones are probably shielded, fast reacting are "bare". CURIE point is only an issue when you are trying to ACCURATELY read 350+/ 50 degrees. BTW the charts say the junction is accurate to 0 degrees F, but the millivolts are so low you need amplification to measure. 1 to 2 % accuracy is a result of manufacturing processes for the gauge unit.

My '00 owners handbook says to not worry if vehicle speeds are 35 or under and they had a chart for cool down periods. In true owner fashion I have generally ignored that except for driving about 4 miles on city streets after a run, but mostly since that is how far it is to the off ramp. I have probably 5000 cycles on the truck had and have not had issues.

Navistar powered schoolbusses used to be famous for turbo failure unless idled for 5 minutes back at the yard, but that was in 2002. I don't hear of any failures much any more.

Back in the day, the issue was either heat/thermal cracking of the exhaust wheel or coking of the bearing.

YMMV