2001 Malibu 3.1 v6 125,000 miles
On November 1, took car in because water pump was leaking; replaced water pump and coolant. About 2 weeks later, temp spiked dumping some coolant out of overflow. Took car back and mechanic could not find out why it did that but he did replace thermostat thinking maybe it was hanging (even though it tested well). A couple more weeks of driving, temp spiked again. Took it back to mechanic; he suspected perhaps coolant reservoir may be the problem so he replaced it. Again after a couple weeks of driving the same thing; temp spiked dumping some coolant… Each time the temp spiked it was after the car sat over night and the spike occurred after only about 4 or 5 miles, hardly enough under ‘normal conditions’ for the car to get that hot and you could drive the car the rest of the day with no problems. The mechanic did the hydro carbon test of the cooling system to see if hydro carbons were present and the test was always negative and there has never been any coolant in the oil.
This is my daughters car so I traded with her for a few days so I could observe what was happening. What I noticed was as the car was heating up it would never get any warm air blowing through the vents until after the thermostat fully opened and even then it was best when driving. I took it back in and the mechanic did the hydro carbon test under a ‘cold’ condition and found, in fact, there was exhaust getting in the coolant when first started. He then pulled the plugs to test each cylinder and found it to be the number 1 cylinder. He suspects there is a very small leak in cylinder head and is in the process of dismantling the engine. Now hoping that it is ‘just’ the head gasket. He will be checking it to ensure the head is not warped or cracked and at a minimum replacing both head gaskets along with intake gaskets.
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