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Date: Thu, 29 Jan 2004 09:38:33 -0800
From: "Dima" <dimanopsamystems.com>
Subject: Re: Do I need to let my turbo "cool down" for awhile ('1990 C-900T)?
When I researched this question for my '97 900SE, the clear recommendation
was to let it idle a few _seconds_ (like 15 seconds, not a minute or so!)
after spirited driving. However, simply logic suggests that one would not
want to simply shut down the engine after a spirited drive even on a
non-turbocharged cars.
Thanks,
-Dima
"Grunff" <grunffnopsam.com> wrote in message
news:bvauaa$qck1p$1nopsam52899.news.uni-berlin.de...
> dcathey wrote:
> > What's the deal w/ letting the turbo cool down by letting the car sit at
> > idle for a minute or so before I kill the ignition?
> > Is it really something I s/b doing? My Saab runs normal oil, has been
well
> > maintained, and has 110k miles; 5-speed.
>
> When you drive hard (motorway driving, or spirited driving) the exhaust
> manifold and turbo get really hot. So hot they glow a nice cherry red.
> This is hot enough to burn pretty much any oil.
>
> The turbo shaft spins on a film of oil - that's all the bearing is. It
> relies on a continuous flow of oil through the bearing to maintaing the
> oil temperature below oil burning point. Without oil, the turbo bearing
> would be metal-metal contact, and would last a matter of minutes.
>
> If you get the turbo nice and hot, then immediately turn off the engine,
> the oil in the bearing will burn up. Next time you start up, there's no
> oil in there for the turbo to spin on, so it wears a little. Do this a
> few times and it wears a lot.
>
> So what do you do? Let the car idle for say a minute, especially after
> hard driving. This gived the turbo time to cool down.
>
> Later cars (including yours IIRC) have a water jacket around the turbo
> bearing. This helps a lot with the cooling, so idling the engine is only
> really important after a hard run.
>
> --
> Grunff
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