Miller

I've got a problem with my 1990 Legacy wagon. Whenever you push the motor....the radiator stops flowing. It almost looks like it's leaking from the right side of the radiator (Near the coolant reservoir) but I can't see anything dripping out of the hoses down there. The only thing that seems to fix it....is if I leave the car off for a while and let it cool off for a bit....and then it works fine until you push it hard enough again. Thoughts anybody? Oh, and....howdy everybody.