1979-1993 & 94 Conv [Subscribe to Daily Digest] |
pressure when cold is a sure sign of a head gasket cylinder to waterway leak.. most saab head gaskets will start to fail this way.. to be honest i think the way folks are told to check for head gasket failure on this board is misleading..
as the gasket erodes between cylinder and waterway a small high pressure leak occurs allowing running cylinder pressure into the cooling system.. this means that the system is running at a constant system pressure based on the blow off pressure of the pressure cap.. this is 15 psi.. in its beginnings there is no water in oil.. no bubbles.. no oil in water and the always mentioned cylinder pressure test will not show it up..
what i am saying here is simple.. folks who really do have the beginnings of head gasket failure are being given bad advice.. thru this bad advice a lot of time and money is being wasted..
two things should cause the system to pressurise.. the simple expansion of the coolent as it warms up.. its obvious that as it cools down the pressure goes away.. secondly if the coolant goes anywhere near atmospheric boiling point the pressure will start to build up.. this is why the system is a pressurised system in the first place it enables the coolant to reach higher than atmospheric boiling point without actually boiling away.. however pressure is only formed when the coolant reaches this point..
this point is well up the saab temp gauge thow.. but again as things cool down the pressure will go away..
now with a small pin hole leak between cylinder and waterway.. something i think is very common on high mileage saabs there will be a constant 15 psi in the system.. if the system is otherwise generally leak proof this pressure will remain there all the time.. at first this gas only gets into the waterways during the high pressures generated when the car is running and under load..
looking for a pressurized system when there shoulnt be one is about the only sure fire method of diagnosing the beginnings of saab head gasket failure.. forget all the other stuff.. that happens much further down the line..
trog100
posted by 62.254....
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