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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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