OK, so my knowledge of diesels was taught to me by a buddy that has a '01. He woud always let his diesel idle for 5-10 minutes at a cold startup. He always lets it cool down to 300 egt before shutting if off. He said that lets all the hot air get out of the turbo. I can leave my diesel idling some days for more than 5 minutes after a drive and it never gets down to 300. I was letting it get down to 400 before shutting it off but lately I have been lazy and shut it off between 450-500. So my question is...is that really all that bad on a diesel? I read a cummins tech article that said it wasn't necessary for a cooldown unless you had been pulling or at WOT for a long time.

 

Letting the egt's cool down to under 400 is a good practice depending on the rig and the type of pyro and where its at will dictate how fast it gets there.

I can recall every time I shut of my pickup's above 400 degree's, Twice.

I can't say whether or not you being lazy will have any effect on the lifespan of your pickup. I would spend the extra thirty seconds it takes to let it cool down to under 400.

 

I ALWAYS let my Super Phat Shaft 66 cool down to 400 degrees before shutoff and now between all the miles I put on it (roughly 195,000 miles) and its new owner it's still working just like new. Now with my new (had it a little over a year) Phat Shaft 71 I still let it cool down to at least 400 degrees. Last week I pulled my compressor housing off to repaint it and there is still 0 play in it after roughly 60,000+ miles on it. And yes I do use it for racing, towing, daily driving, and pulling.

 

I can idle all day and my egts won't go under 350 unless it's below 0F.

I've been following Cummins instructions which say for normal driving no cool down is required, just shut it off.
Must work since my rigs have over 250k miles each with the same turbos.

After towing hard I do wait for the egts to get down to 350°, it's never more than a couple minutes on a 100° day towing 25k pounds.

 

From what I have read about this cool down period especially after a hard pull is to protect the bearings in the turbo. Since they are oil cooled they claim the oil will crystalize and have premature bearing failure if not cooled down some. My 2 cents

 

I always heard it was because the oil would coke up the inside of the lines if it was shut down hot. The oil sits there and boils like my wifes homemade chili.

 

If you let your EGT to stablize to the lowest point, I don't see the issue other than marketing.. My .02

 

Anybody ever cleaned out a flue from a wood burning stove. If you have that junk is what happens when the flue cools down its like rocks. I suspect that is what happens when you shut down a engine with a red hot turbo the oil turns to little rocks and when you start it back up all that stuff goes to the bearings.
I don't have gauges but I always let mine cool down some after a hard pull or a long run. I don't much like it and some of these people in camp grounds don't like it but they will have to live with it I do.

 

On a towing or hauling (truck camper) trip, I shut off the A/C well before my planned stop and then idle to get it close into the 300's on the pyro before shutting down.
If just running empty, I still shut down the A/C before stopping and let it idle long enough to get the turbo shaft speed down. The pyro is usually close to 300°.
Border crossing is the worst. I haul the camper and tow a trailer. I often hit the low traffic crossings and they want the truck shut down immediately on stopping. I learned to coast that last 100 yards.