Chevrolet Repair: 2000 malibu thermostat, intake manifold gasket, coolant tank

Question
Hi there. I have a 2000 Malibu with the 3100 V6 engine ...automatic and a/c . My coolant level drops occasionally but never overheats. The other day with normal operating temperature my coolant tank overflowed substantially. I refilled the tank to the specified level and it was fine for a few days and then it overflowed again...no leaks visible at the water pump. Could this mean thermostat replacement is necessary? The coolant is quite dirty as well.
Thank you very much for your help.
Kelly  

Answer
Hello Kelly, You most likely have a small leak in the cooling sytem. The most common place to leak is the intake manifold gasket. This can leak inside the engine where you can't see it. It will then mix with the oil. The other place is at the ends of the intake manifold, it will leak at a small rate and you might never see any coolant on the ground. I would have it looked at to be sure.

Hope this helps

Have a Nice Day    Mark