I have an old 1991 Cavalier 2L OHC SRi that I've owned for 14 years. Its covered 135,000 miles but still drives well for it's age.
Recently it's developed a problem with the cooling system temperature.
When moving at normal driving speeds the temperature gauge appears normal - although it does sometimes creep up just slightly and then go back to normal for no apparent reason.
When I get stuck in slow moving traffic or stop, the temperature rises much quicker than it used to. The fan is working ok - it switches on when the gauge reaches 90 (which it always has done). This brings the temp down to just about normal running temperature, perhaps just above.
There is a small amount of spitting of coolant around the outside of the header tank (coming from the cap I think) and I do get a small amount of greasiness on the inside of the header tank suggesting there could be a head gasket problem. However, it's been like that for quite sometime and I've not noticed the temperature problem before. The coolant level does not drop and I've not found any water in the oil. The engine does not appear to have lost any power.
The thermostat was replaced a few months ago (it was running too cool but the new stat fixed that). The radiator, header tank & cap have all been replaced recently too.
What I should try next?