I notice that when I’m stuck in traffic, my car starts to overheat. Turning on the air conditioning drops the temperature back down. The temperature is fine going down the road at 100 km/h or so. Any ideas?
There could be several issues here. The first thing to do is check the coolant when the engine is cold. Ensure that it’s clean and filled to the correct level. Your vehicle being a GM product, should have orange coolant; if it’s any other colour, flush and replace it (other manufacturers use green). If you have to refill the coolant reservoir often, it may indicate big trouble somewhere in the engine, perhaps a leaky cylinder-head gasket. If the coolant has never been replaced – the useful life of a coolant is about 10 years, regardless of mileage – you should probably do that, too. Next, check your radiator cap and make sure it’s on tight and in good condition. If the seals in the underside of the cap look brittle and cracked, they’ve probably failed. The coolant system depends on everything remaining tightly sealed, otherwise it can’t pressurise and the coolant will boil, causing a spike in temperature in some very critical places – such as the cylinder head. If the problem persists, it’s possible your water pump’s gone bad and can’t circulate enough coolant for the engine, driving temperatures up while you’re sitting at idle.