03 Pontiac Grand Prix SE 3.1 Ltr.
Im being passed down a problem vehicle that is known to overheat. Previous operator says he was told it had a leaking head gasket and was recommended to pour in a multipurpose sealer into the radiator. Which he did but says he was unable to put the entire amount in since the radiator was full. The bottle of sealer looks to be only about 6oz. And says can be mixed with any antifreeze. The car didnt get ran much after that. Just to the local market and such. Then sat for 2 months.
My observations and symptoms;
Oil is milky which I attribute to head gasket leak. Drained and replaced oil and filter. Drove vehicle for 40 minutes to an hour on the interstate and the temp stayed below normal. Right below 160. The heater does not put out warm air. When exit the interstate the temp begins to rise gradually but not abruptly. I stop and add about a half gallon of water to reservoir and a little to the radiator. As long as the vehicle stays moving the temp stays around 190-200.
Im sure there's a gasket leak but whats with the heater and do you think I can get away with doing another sealer but properly. By flushing and let the sealer have overnight to work?