Is Coolant Overflow Related to the Thermostat?
2 Answers
Coolant overflow is not related to the thermostat. It is generally associated with blockages or poor flow in the upper water chamber of the radiator or the return hose from the upper part of the thermostat to the expansion tank. This happens because the coolant in the lower water chamber of the radiator and the water pump inlet pipe is in a negative pressure state. If the throttle is suddenly released or the engine is shut down, the water pump's efficiency decreases or stops working. There are two scenarios where the car does not overheat but the coolant reservoir overflows: 1. Coolant overflow occurs when the accelerator is pressed hard. This is mainly due to large gaps or cracks in the wet cylinder liners or cylinder head. During engine operation, the pressure of compressed air or combustion gases in the cylinders exceeds the pressure of the coolant in the cooling passages, allowing these combustible gases to enter the engine's cooling passages through the gaps, resulting in coolant overflow from the reservoir. 2. No air is present in the coolant during engine operation. Whether the coolant temperature is high or low, pressing the accelerator does not cause coolant to spray out from the filler cap, but releasing the accelerator causes coolant to spray out from the filler cap.
Coolant overflow can indeed be directly related to the thermostat. Having driven for over a decade, I've encountered this issue several times. Once while driving on the highway, my engine temperature suddenly spiked, and the radiator started spewing coolant, which gave me quite a scare. When towed for repairs, the mechanic explained that the thermostat might have been stuck in the closed position, failing to open, which disrupted coolant circulation. This built up high pressure in the system, causing the coolant to overflow. Similar situations can also occur if the cylinder head gasket is damaged, allowing hot gases to enter the cooling system and forcing water out. However, thermostat failures are quite common, especially in older cars where rust may cause it to stick or seals may deteriorate. It's advisable to regularly monitor the engine temperature gauge and address any abnormal rises early to avoid costly internal engine repairs. Regular checks of the cooling system and thermostat can save a lot of trouble.
