Date: Thu, 29 Jan 2004 12:26:46 +0000 From: Grunff <grunffnopsam.com> Subject: Re: Do I need to let my turbo "cool down" for awhile ('1990 C-900T)?
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