I don’t understand what I’m observing in my cooling system. When driving without stopping, the temperature gauge is exactly where it belongs; however, on stopping to inspect the radiator, I find that the expansion tank is filled to overflowing, with air bubbles bubbling from the overflow hose.
If I shut down and let the engine cool down fully, I expect the coolant to get sucked back into the radiator, but it doesn’t: I’m left with a filled-to-the-brim expansion tank, and a radiator that wants more coolant.
Also, if I drive in a stop-and-go situation (i.e.: traffic lights and stop signs), then the temperature gauge will climb into the red until I get going at a regular, steady speed.
I replaced the thermostat, but that changed nothing. The fans work perfectly.
Does anybody have any idea what this could be?