Based on BB and manuals, I've been waiting 30 sec or longer to prevent coking, etc, before switching the engine off. My mechanic, who has a lot experience with Volvo RWD turbos (formerly a dealer shop foreman before going independent), states that all required is to have it at idle before switching off. Any opinions on how long to idle to cool down the turbo before turning off? Trying to separate fact from myth with this query.

Guri R
'83 244T
'95 945T

Heck, I even let my old Ford lawn tractor cool down at idle for 15 seconds before shutting it off after 3 hours of cutting the lawn! Any engine can stand a couple of breathing spaces after running hard, just to stabilise things.
JD

Thanks for the responses. Sounds like a complete consensus for my driving habits. It looks like I can save myself a few seconds each day.

Guri R

What you're doing is probably not necessary, as the others have said, unless you've really been pushing it or cruising on the highway for a while, but it will definitely not hurt anything. I do idle the 240 before shutting down, because it's not a water-cooled turbo. I remember pulling off the highway at night in my 83 242ti after several hours at 70+mph, opening the hood to reconnect a cruise control line that slipped off, and seeing the turbo housing & manifold glowing from the heat. About a minute at idle and it cooled down. I'm not so worried with the 780, but by force of habit I let it idle for at least a few moments after any fast or aggressive drive. The other preventive measure I'd suggest is a switch to synthetic, it is apparently much more resistant to coking.
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Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina

I have to agree with your mechanic, unless you've really been flogging it.
Coolant continues to circulate through the turbo, even after the engine is shut off; 'course if your turbo isn't water cooled, it should be.

Turbos, on any type of equipment (and my back ground is in diesel mechanics, where everything is turbo charged) must be cooled for longer life.

Cooling is accomplished by , collant and oil circulation.

When you work the turbo hard ie racing, heavy highway work, heavy loads, heavy throttle, etc, it is wise to not shut off the turbo , (engine) losing collant and oil circulation until you have reduced turbo temperature.
Reducing high throttle use, for a couple of minutes, when you come off the highway and use less throttle on secondary roads, this is normally enough to allow shut down.

The only time you should need to idle a turbo charged engine before shut down, is when you have extreme heat from a heavy work load application.

Hope this helps.

John
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90-740GL , 92-945Turbo

I do a lot of uphill driving so I tend to let it cool down for about a minute or when the electric fan has switched itself off. Nevertheless, I killed the car and the turbo now so it's too late.