AR 4 S.S.S.

This is my first turbo, and heard that its a good idea to leave your car running after you have been driving for a while becuase its not good for the turbo to just shut it off. Is this true? Is there some rule of thumb, like if you drive more then 60 minutes let it idle for 5 or something?...thanks

Rally_nutcase_1982

while driving with AC the entire engine compartment becomes very hot. Sine I'm paranoid about blown turbos I usually open the hood (if it's really hot) and let her run for a couple of minutes.
The "secret" is to have always enough oil in your engine, that is the lifeline of your Turbos.

After long highway drives most people get off the throttle and shift earlier (high gear-low RPM) 1-2 miles before the destination/exit, that too helps to cool down the Turbos.

LCP

...use boost sparingly the last minute or two and shut the car off.

Rally_nutcase_1982

These 2 minutes could spare an easy 10K bill in a long run - but hey, that's just my way of thinking ;-)

TurboBob

You're trying to cool down the the bearings and the impeller shaft by flowing cooler(cooler than those parts anyway) oil over them. It's not that the heat is so bad for those parts, they certainly function at much higher temps than you'd shut down at, but after shut down, oil thats in the turbo just clings to those surfaces(like a good oil should) . If the turbo is too hot, the oil will bake and leave a residue on those parts, this is called coking, this residue will come off in tiny pieces at the next start up and gets into the seals causing excessive wear and eventually premature seal failure. If you choose not to cool down on a regular basis, coking can also result in premature wear in the bearings. That being said, a 30 second cool down is usually plenty after normal driving. But at the end of a "spirited" drive shortshifting or just easy driving can allow airflow through the turbo to help the oil cool things.

RMcQ

1. turbo failures on these cars are more due to manufacturing defects in the turbos than mistreatment.

2. turbos only get really hot under boost. If you were running them hard you probably can cool them <b>better</b> by driving gently without boost and with airflow to the intercoolers and radiator than you can by idling the car.

3. The turbos are cooled by oil, but they are also cooled by water (coolant). In fact, the coolant is circulated by an electric pump after shutdown which in a way is a bit of a factory 'turbo timer.'

So in conclusion my opinion is that idling the car after you park it is unecessary in everyday use as long as you can drive the last couple minutes of your trip while staying out of the boost. If for some reason, like a track event, you are wringing the car out and then pull directly into a paddock to park I would certainly idle the car with the hood up for several minutes.

More info from the 2.7T self study guide on the V51 coolant pump:

<i><b>Electrical coolant circulation pump V51</b>

Electrical coolant circulation pump V51 is
located in the engine's V angle.
If the coolant temperature is too high,
thermoswitch for coolant circulation run-on
F95 activates the additional coolant function.
The high temperatures which occur at the
exhaust gas turbocharger produce vapour
bubbles which prevent coolant being drawn in
by pump V51.

When pump V51 starts up, the coolant flows
through the exhaust gas turbocharger and the
cylinder heads. The direction of flow in the
turbocharger cooling circuit is reversed by
this.

Due to this reversal of the direction of coolant
flow, coolant is drawn in via the cylinder heads
(large cross-sections), which means that any
vapour bubbles which develop are expelled
from the exhaust gas turbocharger lines.
The electrical coolant circulation pump again
draws in coolant along the rear coolant pipe,
thereby recirculating the coolant.</i>

Troy H

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LCP

...there was a reason the k03 turbos were redesigned for the '01 models -- the oil lines and passages in the turbos were too damn small and the metallurgy wasn't up to the heat stress. Then there are boost leaks overworking the turbos. Fix those and rarely worry about turbos.

Unless you're at the track, drive easy the last minute before your destination and don't worry about it.

Rally_nutcase_1982

A stock allroad should be able to handle everything if well maintained and properly treated. IMHO the car is just a bit on the heavy side and track days would need special preparation for the car.

But after all the Italian, German or French cars that had a Turbo (and most of them blew the Turbo), I'd still prefer the "old fashioned" cool down method. Maybe newer technology doesn't need all that care and latest oil developments do their part, but I frequently remember all the $$$$$$$$$ spent in the past on Turbo/engine replacements - it could be a nice Lambo or 911 today ;-)