I have a problem with my cosworth, i have only just got it and every coulpe of days it with overheat really quickly, when it does the cooling system is pressurised and the top hose nothing but steam in it and the header tank is full to the brim. If i vent all the steam off it empties the tank and i can fill it again whilst bleeding it from the top hose. looks to me that it may be an airlock somewhere but i was wondering if anyone had heard of this before.