Expert: Sean Halliday - 9/17/2008

Question
QUESTION: I have an 87 Saab 900-no turbo...Replaced the thermostat, but pressure is still building up in the Reservoir and leaking out of the cap. car also overheats.  I checked hose placement. can't think of anything else to do ?  any suggestions or comments.

ANSWER: Sounds like a leaking head gasket.You will need to have the head checked by a shop for a leak down test.Only a shop can do this and blown head gasket is the only cause of built up pressure in the cooling system.

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QUESTION: would air coming up through the hose's into the reservoir be from the head gasket also ...almost look's like the coolant is boiling..

ANSWER: Yes,thats the symptoms for a leaking gasket.The gasket blows across the water jackets and the compression from the piston leaks into the cooling passages.

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QUESTION: Is there any less expesive problems it could be? Air lock ?


Answer
Its the only possible cause as these are the symptoms of a blown head gasket.Air lock will not do this as it would only cause the car to run hot and not bubble the coolant like you said.Leak down test for a 100% verification of this will tell you this is the case.