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Re: fan does not run on... Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 30 Jul 2003 06:39:38
In Reply to: fan does not run on..., shawn, Wed, 30 Jul 2003 04:08:09 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The fan runs if the radiator temperature is hotter than the set point of the thermofan switch- typically around 89C. This only blows air over the radiator to cool the coolant. Yes, some air may hit the turbo, but it's the water jacket on the turbo that does the cooling.
On the '88, there was a time delay relay that would allow the fan to keep running for up to around 10 minutes if the radiator was hot. This time delay relay would occasionally fail on, running the battery down. Saab had a service bulletin to replace the relay with a standard relay - the fan would stop when the ignition was off.
Perhaps that service bulletin was done to your '95.
Of course, if the radiator isn't getting hot, then the fan won't run. But if it was running right up until the ignition was turned off, then I can't believe it suddenly cooled down the second the key was turned off. My guess is that the bulletin was done.
Again, the actual value of running the fan once the engine is stopped is minimal. If the engine isn't running, neither is the water pump, so the cooler coolant in the radiator is going to stay there.
The turbo is primarily oil cooled, and oil only flows when the engine is running. The turbo does have a water jacket - the purpose of the water jacket is to provide a large thermal mass to absorb the large heat fluctuations that turbos produce. When the engine shuts off and the oil flow stops, the heat in the turbo has really no place to go, and the temperature can rise quickly. The water in the water jacket absorbs that heat and limits the temperature.
posted by 192.249....
, Wed, 30 Jul 2003 06:39:38 <-- Viewing This Message
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