Got a question what would cause my cooling system to build up
So much pressure it blows a radiator

 

My guess is just a defect in the radiator.

 

Leaking cylinder head gasket.

 

corroded radiator or a bad water pump/thermostat with a failed pressure relief valve. If you are not seeing the temp gauge spike high, then it will almost be garanteed to be a bad radiator.

 

Test you pressure cap to make sure it is working by releasing pressure. But it will only need to work if the car is overheating. Is it?

Now if the pressure builds up real fast, like 30 sec, it is the head gasket. You can use a tail pip sniffer by the cap, with it off, to see if it detects any exhaust fumes. It should not.

 

Water caused mine to go super pressure, correct coolant fixed it.

 

innzane's comment may sound odd to some, but it's accurate. We use antifreeze because it boils at a high temperature than water. Why does it boil at a higher temperature? Because antifreeze has lower vapor pressure than water. And lower vapor pressure means less pressure inside our car's coolant system & radiator.