I have a 1998 Pontiac Transport. The radiator was replaced recently. We also replaced the radiator fan and the thermostat. The spark plugs had been gas fowled and we replaced them. Well my husband went to check the radiator fluid and it exploded all over him. The vehicle was not running nor was it hot. Why would it have built up pressure without it being hot?
It can take many hours to cool down and for the pressure to go down. There's also the possibility of a leaking head gasket that leaks combustion gas into the cooling system, although typically that kind of leak will also bleed pressure off rather quickly after stopping the engine. Wouldn't hurt to have the radiator cap tested for pressure. It should release any pressure over about 15 pounds.