Newbie turbo question
 

I just got an 85 300sd this week, and have a simple question about the turbo. Do I need to let the car idle down after running to cool the turbo off? I have been doing this, but is it really needed?

Turbo Cool Down
 

It's a good idea to let it idle for a short period before shutting off the engine, especially if you have been on the highway recently. For example, you would want to let the car engine idle for about a minute if you were to pull off of the highway at a rest stop. These engines run on boost 100% of the time when you're on the highway, and the turbo is working hot and hard.

However, if you're on your way home, and you drive gently through your neighborhood before pulling into your driveway, there really isn't any need to let the engine idle before shutting it off.

It all depends on how hard you've been working the turbo prior to shutting off the engine.

Don't shut it down at the top of the ramp immediately after a 80+ mph run. VeeDub pretty much summed it up.

I think the basic idea is that you don't want to shut the car off (and the oil supply) while the turbo is still spinning at ungodly speeds.

These turbos are oil cooled, so if you shut the engine off with the turbo hot you can fry the oil since it stops moving. The resulting carbon (coke) on the bearings is VERY hard and wears them out.

Interstate rest stops are hell on turbos -- you are flying along, pull of, and within seconds are at a full stop. The turbine is still red hot (or hotter in the mountains!), and if you just shut right off, you have trouble. It wont' be turning fast, just hot.

A minute or two idle time will cool it off enough to be safe, especially if you use synthetic oil, as I strongly recommend with turbos. A couple or three blocks of city or suburban traffic is equivalent to the minute or two of idle, but if you want to play it safe, get in the habit of letting the car idle a bit before shutting off, then you won't forget on the interstate!

Peter