MtnDodge

I keep seeing things about not shutting the truck down when it's hot. Since this is my first diesel I'd like to find out what I can about this issue. Why? What constitutes 'hot'? What are the alternatives?

Thanks for any info you can pour my way.

Jeff in TD

If you look in the owner's manual, it gives suggested cool down times. If you are just driving around town with no load, the time you pull to the curb, set the parking brake and unhook your seat belt is probably sufficient.

If you were just pulling up a mountain floored and towing heavy, several minutes of idling would allow the turbo to cool down.

As I understand it, the issue is that exhaust temp flowing into the turbo can get up around 1200 degrees on a stock engine when pulling hard, and some of that heat conducts up to the turbo shaft and into the turbo bearings. No motor oil can withstand 1200 degrees without breaking down and carbonizing, but when the engine is running quite a bit of oil is flowing through the turbo bearings which prevents both the bearings and the oil from getting too hot.

If you shut the engine off immediately after pulling hard, you stop the oil flow through the bearings while the turbo is still very hot. This is hard on the turbo bearings, and also upon the next startup the oil in the turbo is likely to have been broken down by the heat that was present on shut down.

If you let the engine idle, exhaust temps soon fall to about 300 degrees and the turbo cools down while oil is still flowing.

An exhaust temp gauge is a nice addition to a diesel, especially if you tow, or do performance mods. Folks also like to install aftermarket timers that can be set to automatically allow the engine to idle for a preset amount of time before shutting it down, so you don't have to wait around.

DaveB.inVa

Some folks nowdays will say its not needed, however I don't see how it can hurt and personally I do let my truck cool down before shutoff.

The main concern is shutting down with the turbo still being very hot, resulting in oil coking in the bearings.

Personally I shut down at 300 degrees on my pyrometer.

To monitor your truck adequately you should install a boost gauge, EGT gauge and for you a trans temp gauge.

This should be the very first thing you do.

packard8

The main concern is the bearings in the turbo. If you've just pulled a long steep grade towing heavy your turbo is near red hot. When you get to the top and pull over and shut off the engine the oil in the turbo bearings/bushings will "coke" or carbonize from the heat.

If you let the engine idle for a few minutes things have a chance to equalize the heat load and cool down while the oil is still circulating. Personally, the only time I worry about it is when the engine has been working hard. If I'm just pulling into the grocery store parking lot I just shut it off without a "cool down".