Most turbos use about a quart in 1-1.5k mi.. Is it being burned in the cylinders or is it lost in the turbo seals? thanks carl

 

Oil is being used as a coolant, even though our engines are water cooled. Being "boosted" there is a situation where oil is passed through guides and rings and burnt in the cats. The turbochargers will pass oil at the sealing rings. If you do not allow the engine a 2 minute cool down period prior to shutting the car off, you will smoke your turbine side sealing rings. This will lead to excessive oil consumption...

 

I never allow a 2 minute cool down and oil consumption is down to 1 quart per 4,000 miles. Most of my driving is commuting, so there is no recent track use. With the fans running for quite a while after shut down, I'm reasonably confident that the old 2 minute guideline is no longer helpful. AS

 

Alexander;

How do you make a statement that the 2 minute guideline doesn't apply. I see 6ea 996TT turbochargers a week on average. I can tell who does the hot shutdowns and who doesn't. The fans don't have anything to do with the turbochargers as far as there health. The decklid fan will turn on to pull the heat away from the engine compartment. Alot of it comes from the heat radiating from the hot turbine housings. You can do what you want and how you want. The fact is, if you don't idle the car, and are shuting the engine off, excess heat is transfered from the turbine housing, through the turbine wheel (like a wick), and this cooks the seals. I have seen these units fail within 1000 miles.

Are turbochargers are not water cooled, they are not air-cooled, they are oil-cooled.. They need a constant supply of cool oil, with a rich AFR on the idle circuit to cool the turbine housing down, this also cools the turbine wheel. If you are coasting along your block, your AFR's are lean, not rich! This doesn't benifit the turbine housing.. We want the air/fuel mixture on the idle circuit to cool things down. This is an insurance policy.. Drive the way you want.. Save your $$$ for when your turbochargers start to puke oil..

 

Kevin,
I appreciate your insight. In my case, it's not realistic for me to sit in a parking lot for 2 minutes each time I arrive at my destination. I hope to put over 100,000 miles on my car (typical for me), so I'll let you know how my behavior impacts longevity. Since the entire engine is a large heat sink, it's hard to see how much heat will be dissapeted in 120 seconds. Don't you think it matters how hard you've been driving before shut down. My intuition could be all wrong, but I'd see 10 hard track laps on a hot day being much different than a 75 mph highway cruise with a two mile urban stretch before shut down being much different circumstances.
I don't doubt your insight. It just seems that there are more variables than the 2 minute guideline. For red hot track use, maybe 2 minutes isn't enough. For sedate street driving, it seems to be somewhat obsessive. Time will tell, and if my experience proves me wrong, I'll confess. AS

 

The responses have diverged a bit from what I believe Carl was asking about. As Kevin said, there may be some oil being passed around the turbocharger seals. A more significant depleter of oil may be that on cold starts, many TT engines will emit a short billowing poof of white/blue smoke out the exhausts. The consensus on this phenomena seems to be that with boxer engines, the TT motor in particular, there will be small amounts of residual oil that collects inside the cylinders after use (such as resting overnight), which is then blown out upon cold start up. Long term oil consumption appears to relate directly to how well the motor was broken in, your driving style, how you shut the car down, and so on.

Carl, if you do a search of the forums, you'll find that this subject has been flogged ad nauseam. fwiw.....

Jeff

 

The "turbo cool down" issue is an interesting one. I have always allowed the engine to idle for at least a minute no matter what. I do this to make sure that the turbos are all fully spun down. If I've been driving hard then I will definately let the car idle longer. I do think it makes a difference.

However, from turbocharged airplanes, which often have temperature gauges on their turbos, I know that it can take significantly longer for a turbo to really cool down. Sometimes it is necessary to idle for 5 minutes or more. I guess the same can be true for some trucks? But maybe the difference is the types of turbos and the lack of additional cooling mechanisms on these turbos once the engine is shut down.

On my Turbo I don't mind the extra time it takes. My Audi S4 is probably more critical than the Turbo (because it lacks the additional oil supply after the engine is shut down). That car is more of an annoyance. Probably because of the different types of tasks it is used for.

Stephen

 

kevin,

So does this 2min cool down apply to a trip to the mall.... i can't imagine letting the car idle for 2 minutes in a parking structure....

But if you tell us we should, then i will obey..... But what do i tell the valet????

 

rinlv1, 2 minutes is 2 minutes. So people drive harder than others, some conditions are harder than other geographical areas. I have posted pictures of low mileage burnt shafts. If you can't do 2 minutes, do at least 30 seconds.. But try to do 2 minutes.. You guys keep me busy.. I'll post a picture of a hot shutdown and what the heat does to the shaft and bearings...

 

I have always tried to idle my Turbo for 2 min, but sometimes it's a matter of getting as much as I can short of that. My minimum idle time is 45 sec. if the car hasn't been run hard.

My answer to the valet question is ...I don't valet park if I don't get to drive the car to the parking area..

 

Valet?? you must be kidding!!! who here would give a 996 turbo to a valet??!! didn't you see "ferris bueler's day off"??
if you use valets the turbo cool down will be the least of your problems!!!