Turbo idling

[PXW]

Bit of an oddball question. Was sat in traffic the other day, when the car did its economy engine shut off thing (yes, it's a BMW, but most cars do it nowadays). During the lull, I was thinking back to the old days driving SAABs turbos, and the standing instruction that after a fast run you had to idle the car for a few moments to cool the turbo, to avoid cludging the insides up with glazed or brunt on oil deposits etc.

So, the question: what changed? Obviously the modern turbodiesels don't need to idle - but I can't immediately think of why that might be. Thought someone on here might be able to help me out in my 'idle' curiosity...

 

[JohnBar]

I think that modern turbos are water cooled. The older ones were oil cooled and the oil carbonised in the lubrication channels and caused seizure. At least that is my understanding.

 

[thejohn]

But I understand that the oil is the bearing so you need to run the engine until the turbo slows and keep the oil flowing to prevent wear to the turbo and wear will result in the turbo vane striking the turbo body and then that will result in metal being ingested into the engine.
John

 

[balge]

I was under the impression the reason you used to have to let the engine idle a bit before shutting down turbos was to let the shaft slow down so it didn't run too long without oil pressure when the engine stopped?
Maybe they use sealed bearings now?

 

[Druk]

I was under the impression the reason you used to have to let the engine idle a bit before shutting down turbos was to let the shaft slow down so it didn't run too long without oil pressure when the engine stopped?
Maybe they use sealed bearings now?

That is the correct reason.

 

[Auto-mobile]

Just add it to the other components that will prematurely fail due to stop/start "technology"

 

[PXW]

Thanks all. Will start saving for when it falls apart!

 

[jamesfuller]

Is that why BMW turbos don't usually make it past 100k?

 

[PXW]

Is that why BMW turbos don't usually make it past 100k?

Don't think the technology is fundamentally different from make to make. As far as I am aware there are plenty of high mileage BMW turbos out there - autotrader presently lists1200 BMW vehicles over 100,000 miles and under 7 years old (Versus c.500 Mercs!). Not having a dig, but was there any basis for your statement or was it just a BMW/merc thing? If there's any evidence is certainly like to know about it, given that I'm likely to run my present BMW up toward six figure mileage!