Can someone tell me why coolant residue keeps reappearing near the cap of the overflow tank? I had the coolant changed 20k ago, same issue then and now. I have the Toyota red coolant in it, always did. It looks like it's boiling over the top of the tank but there never appears to be any missing and the line is on the HOT when hot. It doesn't overheat. I've been thinking about the radiator cap being bad, but I'm not sure. Any ideas?
Thanks