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A piece of advice that seems to be widely accepted is that after a long high-speed run, when the turbocharger is thoroughly hot, you should let the engine idle for a while before stopping it. The reason given is that this allows the extremely hot turbo bearings to cool down a bit while the lubricating oil is still flowing, so that the bearings don't get contaminated by burned-on deposits.

I can understand this, and I can also understand the advice that often comes with it, namely that normally it isn't very important because at the end of a typical journey there will be quite a few miles of relatively slow driving between leaving the motorway and arriving home.

Here's my question. If it's all true, why are we not told to let the engine idle for a while before filling up at a motorway service station? I've never known any expert to give this advice; equally, I've never seen cars waiting before the pumps in a service station with their engines running.

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FWIW, I have been instructed by heavy duty mechanics trained by both John Deere and Caterpillar to allow turbochargers on large diesel powerplants to cool by idling for several minutes before shutting down. I also know the failure of turbocharger bearings to be a common problem on heavy equipment where engines are regularly shut down without a cool-down period. –  alx9r Jan 23 '13 at 9:11
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4 Answers 4

If you have a highly tuned performance car you are told to idle for a few minutes before you roll up to the pump, otherwise you can destroy your turbo.

I regularly see other tuned Japanese cars idling while i do this. It's also a good opportunity to talk cars with other petrolheads.

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You're also not told about not riding on the clutch, keeping below 3000 RPM when the engine is still new (less than about 5000 miles on the odometer), and a few other things.

I wouldn't worry too much about it. If you live in a suburb, or anywhere that has a speed limit of 30mph/50km/h for that matter, chances are that by the time you get home and into your garage/parking bay your turbo would have slowed down enough for you to safely switch your car off.

This topic is also why it is a good idea to have a bigger intercooler and possibly a water/meth injection kit fitted to your car if you can afford it.

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The owner's manual for my turbo Eclipse specifically mentions cool-down time periods, with the times listed based on the type of driving that was done.

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That's my favourite car from Need For Speed: Underground 2. –  Juann Strauss Jan 23 '13 at 15:40
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You should whenever possible let the engine idle for a short period of time to allow the turbo to cool in big trucks and cars alike. It will definitely add life to your turbo.

If you are keeping relatively low speeds and minimal boost in the last few minutes of your drive such as in your neighborhood or long driveway then the time needed to allow the turbo to cool will be reduced or eliminated. Coming off the freeway and shutting off the engine immediately would almost certainly reduce the life of the turbo.

They make a device to help with this called a Turbo Timer

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