Date: Fri, 28 May 1999 08:38:29 +0200
From: Robert Brown <rjbnopsamnet.se>
Subject: Turbo bearing damage [was: when can i take a road trip?]


Hi again, changing subject line so it's more relevant (reposting, too) . . . // R > Hi, comments below . . . Regards, Robert > > Pierrick Brenot wrote: > > > I almost always respect the 5-10 seconds idle before shut down, and more > > when I have driven fast using a lot of full boost. > > Must admit that I also wait after driving hard, regardless of what the Saab > people say, no offence intended them ;-) > > > > > Do you mean that I could ignore this simple rule after a normal ride ? > > My 900 is a 16VTurbo MY1991. > > As I write this, I'm hoping that someone (such as a mechanic with knowledge of > materials wear in exhaust-driven turbines) will magically pop up and help out in > the discussion. > > The line of reasoning I received was that the water cooling will suffice to hold > surface temperatures sufficiently low - and ensure that the oil maintains its > lubricating properties - while the turbine winds down. Both the water and oil > have stopped once the ignition is off. > > For the _older_ turbos, shutting off the engine without prior idling meant that > the oil stopped, some evaporated due to high temperature, and a quickly-spinning > turbo would spin on a relatively dry bearing for too long. After a couple of > years or so, you got the chance drive down the street with lots of nice white > smoke pouring out (just as they did back in the old turbo Formula 1 days). > > I nonetheless have doubts concerning whether the water cooling is sufficient to > prevent premature wear, in the cases where the turbine is spinning quickly > immediately prior to shutdown. > > My advice, for what it's worth, is that you can park and pull out the key > straight away if you've taken it easy during the last 1/2 - 1 minute or so. > > But I don't know from what year Saab compressors got water cooling. Let's hope > that someone else reading this knows more than I do ... > // Robert (1999 9-3 200) > > > > > > > thanks in advance > > ck > > 1991 900T > > > > Robert Brown <rjbnopsamnet.se> wrote in message > > news:374C5BFA.6171EAA7nopsamnet.se... > > > > > > Another tip - the turbo bearings are now watercooled which means that the > > > instructions on earlier models - "idle 15 seconds before shutting down" > > can be > > > ignored to a certain degree, though you may like to exercise due care. Any > > > comments from turbo owners out there? > > > > > > Robert B in Gothenburg (drives an '83 900 and sometimes gets the keys to > > his > > > girlfriend's 9-3 200T. Aren't girfriends fun) > > >

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