Never remove the radiator cap under any conditions while the engine is running! Failure to follow these instructions could result in damage to the cooling system and/or personal injury. To avoid having scalding hot coolant or steam blow out of the radiator, use extreme care when removing the radiator cap from a hot radiator. Wait until the engine has cooled, then wrap a thick cloth around the radiator cap and turn it slowly to the first stop. Step back while the pressure is released from the cooling system. When you are sure the pressure has been released, press down on the radiator cap (with the cloth still in position), turn and remove the cap.
Fig. Cut-away view of a typical cooling system flow