Why is it not safe to open the radiator cap when engine overheating?

It is not safe to open the radiator cap when the engine is overheating because the cooling system is pressurized. When the engine is running, the water pump circulates coolant through the engine block and cylinder head to absorb heat. The coolant then flows back to the radiator, where it is cooled by the air flowing through the radiator fins. The pressure in the cooling system helps to keep the coolant from boiling at a lower temperature, which is important for preventing engine damage.

If you open the radiator cap when the engine is overheating, the sudden release of pressure can cause the coolant to boil violently. This can spray hot coolant and steam out of the radiator, which can cause serious burns. It can also damage the radiator and other components of the cooling system.

If your engine is overheating, it is best to let it cool down before attempting to open the radiator cap. You can turn off the engine and allow it to sit for a few minutes. If the engine is still hot, you can add coolant to the overflow tank. Do not open the radiator cap until the engine has completely cooled down.