924Board.org

[924TurboSA]

Hey everyone not sure if this post needs to go in the other tech section but just had the manifold work done on my new 931.. see post below..and the guy I take it to STRONGLY advised me AGAINST letting the turbo cool down by letting it idle for a few minutes before shutting the car down.

Reason being extreme heat builds up in the manifold while the car isn't moving. It seems from other posts cracked manifolds are common on our cars. He advises taking the drive easy (no boost) a few minutes before you come to a stop as the better idea to allow the turbo to cool.

Any comments?

Thanks
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As your attorney, I advise you to drive at top speed.

[ideola]

Hmmm...that's pretty interesting...although if you added an auxilliary electrical fan, as I plan to do, which blows cool air in that vicinity, I would think that would be less of a concern. Also, I really like the idea of a pre-luber, which can also be used to pump oil to the turbo bearings after shutdown. I have a thread somewhere around here on both of those topics...
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erstwhile owner of just about every 924 variant ever made

[Smoothie]

From what I've read, (and it makes sense, so I have to agree) - you get a spike in engine temp after shutdown. That's because while the engine's running, it's generating heat, but you also have the cooling system at work, recirculating coolant.. Then when you shut down, coolant flow is suddenly stopped, but the engines' built-up heat doesn't suddenly "go away". Generation of additional heat stops, but engine temperature spikes because the effect of the cooling system's been removed from the equation. The usual sequence of events after shutdown is temperature rises above normal running temperature, it peaks, then eventually drops again. This temperature rise after shutdown is commonly referred to as "heat soak".

The temperature spike is going to happen no matter what, but of course its' severity will vary based on what's happened before shutdown. Worst would be to shutdown right after a hard run. Second best (or second worst) would be to go from hard run, immediately to a stationary idle for a while then shut down. Best would be to drive it slow and easy for a while after hard running to give the cooling system and airflow time to dissipate the excess heat build-up, then either shut it down or let it idle some, then shut down. Letting it idle a while isn't so bad. The more important situations to avoid, in descending order of severity, are 1) going straight from hard running to shutdown or 2) straight from hard running to idle.

Long story short, I agree with the advice you were given. In my case, most of the time it's taken care of automatically because I have about 1 mile of lower speed driving between my home and the nearest higher speed road.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Archie9xx]

Being a little (my g/f would roll her eyes now) paranoid about my car's idle-cooling procedure, I usually do the both: cruise in relatively low speed (and revs) for a mile or so and then letting it idle for a minute before shutdown. The car has had a broken manifold several years (but no so many miles) ago, but it was naturally fixed afterwards. So far, no problems.
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931 '79
ex-list:
924 '79
944 '86
931 '79
944 '83
356B '60
911T/SC '70
944 S2 Cabriolet '90
924 '84

[924TurboSA]

Cool thanks for the advise guys.
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As your attorney, I advise you to drive at top speed.

[Dans931]

The owner's manual also suggests idling the car after hard driving. People are curious why I park and let the car run before shutting off. From experiance: when my 82 was retired, it had 185,000 miles on the original turbo which was still working well when the car was parked. I used Mobil 1 and always idled down after driving.
Daniel

82 931 (has VW wires)
84 Jetta Diesel (has no wires)