Hello I have replaced the water pump on my 1979 GMC Calberrro because it was leaking at the water pump gasket on the passenger side. So I replaced the waterpump and gaskets.Two days later it started to leak again so I exchanged the water pump at Autozone and replaced the thermostat with 180* and the pressure cap 16ilbs (they said that was the proper rating). and today when i was coming back from lunch (I drove and had parked it for 20-30 mins)it was leaking from behind the water pump again but it wasnt leaking before i went inside to lunch. And when i opened the radiator the leak stopped. So my Question is the pressure cap on my Car falty or too high? I dont want to change the water pump again until im sure of what the problem is.