The guideline to not open the radiator cap while the engine is hot is true.

The guideline to not open the radiator cap while the engine is hot is true.

• A. False
• B. Not sure
• C. Sometimes
• D. True

Answer: (D)

Opening a radiator cap while the engine is hot is dangerous because the cooling system is under pressure. The cap seals the system to raise the coolant’s boiling point, so when the engine is hot the coolant and steam are at high pressure. Removing the cap suddenly releases that pressure and can spray hot coolant and steam, causing severe burns. That’s why the guideline is true: never open the radiator cap until the engine has cooled and the pressure has dropped to safe levels. If you must check levels or perform maintenance, wait for full cooling, then open slowly only after relieving the pressure.

Opening a radiator cap while the engine is hot is dangerous because the cooling system is under pressure. The cap seals the system to raise the coolant’s boiling point, so when the engine is hot the coolant and steam are at high pressure. Removing the cap suddenly releases that pressure and can spray hot coolant and steam, causing severe burns. That’s why the guideline is true: never open the radiator cap until the engine has cooled and the pressure has dropped to safe levels. If you must check levels or perform maintenance, wait for full cooling, then open slowly only after relieving the pressure.