Can you open a hot radiator while the engine is running?

Never open a hot radiator while the engine is running. Doing so can result in serious injury or even death from super-heated steam and scalding-hot coolant being released into the air. Radiator caps are designed to hold pressure and regulate the temperature of the coolant within. When the engine is running, the pressure inside the cooling system can be extremely high, and opening the radiator cap can cause a sudden release of this pressure. The resulting eruption of hot coolant and steam can cause severe burns or even damage the vehicle.