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Date: Sun, 11 Jul 1999 17:22:30 GMT
From: Paul Johnson <tallweednopsam.com>
Subject: Re: Boil over problem - an update


"George F. Johnson" wrote: > Thanks to everyone who is trying to help. Here is an update on the problem. I > have eliminated the thermostat as a cause. I have said that the boil over only > occurs after shuting off the engine. It occurs to me however that it may be > boiling over while driving and I havn't noticed because the gauge is always > reading normal (in highway driving, the gauge is below the midpoint, sometimes > moving above midpoint in traffic, but never getting into the red zone). > Yesterday I performed a compression test and got 135-140 psi on cyc. 1 & 2 and > 125 psi on 3 & 4. I used one of the old press in type gauges so the reading > may be a bit lower than actual. Seems like a blown head gasket would give a > lower reading. What do you think? I am in the process of flushing the cooling > system with a cleaner that should remain in for several days so I won't know > the results for a while. > > As an aside, I recently did a minor tune up and replaced the plugs. I used > Bosch platinum plugs and after installing them, I noticed that they were > resistor plugs and Saab calls for non resistors in my car. I called the parts > store that sold me the plugs and they said the type of plugs I got only came in > resistor and they would work fine. Seems to run OK, what do you think? > > Thanks again for all the help > George F. Johnson George, If you have a blown head gasket I think you might have more problems than just at shutdown. I'm not sure the pressure difference is all that great except that is is between two adjacent cylinders. They might be leaking between each other. I'd suggest check the pressure cap on the overflow tank and the tank itself. I had a 76 900T that the tank split along the seam but would only leak when there was some pressure in the system. The car ran fine but would mysteriously loose fluid. The split was on the bottom of the tank. As you can guess that took me a while to find. The cap can also go bad and not give you the full 12-14 psi pressure it's supposed to give. At atmospheric pressure (14 psi) water boils at the well known 212F. I just got out my steam table from my thermodynamics class. If the cap is supposed to provide an additional 14 psi of pressure then water in the radiator will boil at 246F. I don't know what the antifreeze does to the numbers because my table is for pure water. The Saab dealer should be able to pressure check the cap and the tank. They have a tool to do that. Replacing the cap or tank is cheap compared to pulling the head and they can be tested with little fuss. Paul Johnson

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