After driving my car at operating temperature for 5-10 minutes it begins to overheat and coolant boils into my reservoir. My thermostat opens at the correct temp. My radiator cap operates a correct pressure. My water pump still pumps. My radiator is not clogged as I've flushed it several times. There are no air pockets to my knowledge because my thermostat has a wiggle pin(scientific name) to stop air pockets. It doesn't leak at ALL. I'm confuzzled.