2004 Gran Prix 3800 6cyl overheated, some coolant & engine oil lost replaced thermostat, No fix. Is it likely head gasket, cracked head or block? Which is most likely?twice
radiator replaced 6 years ago coolant mix seems to have been bad as it looked like rust in cooling system. Thermostat looked all gummy.
Perform a cylinder pressure or leak down test to determine if you have a head gasket issue.
A six year old radiator may need replacement but like Tom said the head gaskets may need replacement. At the very least you need to use a good cooling system cleaner and flush the engine and radiator out really good.
These engines rarely, if ever, blow a head gasket. They are notorious for intake manifold gasket failure though. Both the upper and lower intake gaskets are very prone to leakage. Also, look at the 2 plastic elbows that go from the engine to the belt tensioner. They could be leaking as well. It's best to replace them with the metal elbows that are now available. As suggested above a good flush/cleaning may be needed as well. HTH. -Jim
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