* System Pressure: The most probable cause is excessive pressure buildup within the cooling system. This pressure is normally relieved by the radiator cap's pressure valve, but if it's failing or the pressure is too high, the cap will blow off. The high pressure itself indicates an underlying problem:
* Coolant Leaks: A leak anywhere in the system (radiator, hoses, water pump, head gasket) will cause the coolant level to drop, leading to overheating and increased pressure as the remaining coolant boils. A small, slow leak might not be immediately obvious until the system is pressurized.
* Faulty Thermostat: A stuck-closed thermostat prevents coolant from circulating properly, leading to localized overheating and pressure buildup.
* Clogged Radiator: A radiator clogged with debris restricts coolant flow, leading to overheating.
* Faulty Water Pump: A failing water pump isn't effectively circulating coolant, resulting in overheating in the engine block and increased pressure.
* Head Gasket Failure: A blown head gasket allows combustion gases to enter the cooling system, creating pressure. This is a very serious issue. This will often show up as white smoke from the exhaust as well.
* Faulty Radiator Cap: While less likely than the underlying pressure issue, a completely faulty radiator cap that fails to hold pressure correctly could also be the problem. However, even a slightly faulty cap may allow some pressure release before it blows off completely, meaning a more significant pressure problem is almost certainly present.
What to do:
Do not attempt to drive the car until the problem is diagnosed and fixed. Driving with a popping radiator cap is incredibly dangerous and will likely cause significant engine damage. Have the vehicle towed to a mechanic for a proper diagnosis and repair. Ignoring this problem could result in a catastrophic engine failure.
