My radiator had a crack on the topside of the plastic. I patched it up with JB Weld and added water in the radiator. I was doing that for the past week. A few days ago the pressure made a hole in the JB, so i patched it up again. I was adding water this whole time and not once did it overheat. Today i added a mix of water and coolant and it overheated, why is that?
My car has an automatic transmission.
First of all the radiator cracks cannot be fixed with the sealer. It may work temporarily only until system pressure builds up and it will start leaking again. You are overheating now due to air pockets in the system and will need to purge all the air out of the engine. Also your thermostat may be stuck closed and may need replaced.