1997 GMC Other Repair Question
Hi engine temp. on '97 Bonn. SSEi
Most over heating problems in GM products with that many miles is caused by a clogged radiator. The factory coolant is good for about 50K miles and it looses it's additives and slowly builds up residue in the radiator. It is almost impossible to have the radiator cleaned because of the plastic top. Rodding out is at best a 50% solution because the construction doesn't allow for a 100% fix.
The dash gauge is about 75% accurate. I recommebnd getting an infra-red digital heat gauge. They are about $65.00 and look like a small pistol. You can point and read temperatures.
A catalytic converter can cause an engine to run hotter. Most garages have an exhaust pressure tester and emissions analyzer to determine if you need to replace it.
If nothing else works my recommendations are to replace the radiator. It costs about $250.00. It is a problem that occurs slowly and you don't see it happen. When you replace the radiator, replace the hose and thermostat.
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The problem may be related to the intake manifold gaskets (Upper and Lower). GM just redesigned the lower intake manifold gasket to be metal framed. Use that one if you swap them out. They are famous for leaking and may let water/coolant enter your intake directly. This can cause all kinds of problems. Don't sit on it too long.
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