What Causes Coolant to Overflow from the Expansion Tank Cap?
2 Answers
Overfilled coolant: If the coolant exceeds the marked line on the reservoir, it may overflow during driving. Thermostat malfunction: A faulty thermostat can cause the engine temperature to rise excessively. High temperatures prevent the coolant from circulating properly through the engine's cooling passages (large circulation), leading to small circulation within the radiator and resulting in overflow. Coolant is a crucial consumable in the cooling system, which is an essential component of a vehicle. It helps maintain the engine's stable power output. Many drivers have encountered coolant overflowing from the reservoir, and the reasons include the following three points: 1. Check if the reservoir cap is damaged. High temperatures inside the reservoir can cause coolant to leak if the cap is damaged. 2. Overfilled coolant: If the coolant level exceeds the marked line on the reservoir, it may overflow during driving. If the coolant level is appropriate, overflow will not occur. 3. Thermostat malfunction: A faulty thermostat can cause the engine temperature to rise excessively. High temperatures prevent the coolant from circulating properly through the engine's cooling passages (large circulation), leading to small circulation within the radiator and resulting in overflow.
Coolant overflowing from the overflow tank cap is most likely caused by excessive pressure inside the cooling system. Common scenarios include overfilling the coolant which expands in hot weather with no room left, or a deteriorated cap with failed sealing ring unable to control pressure release. Other factors could be clogged hoses restricting coolant flow leading to rapid temperature rise, or internal engine issues like a blown head gasket allowing exhaust gases to mix in and create additional pressure. Don't take this lightly – continuous overflow may cause severe engine overheating damaging components, or even scalding injuries from leaking hot fluid. Recommended action: Park the vehicle and wait for complete system cooling. First, check the coolant level remains between MIN and MAX marks; replace the cap if visibly deformed or stained; have professionals conduct pressure tests during routine maintenance for preventive measures. Developing good maintenance habits ensures safer and more reliable driving.
