What are the phenomena when the thermostat is broken?

If the thermostat of the car is broken, then the most obvious symptoms will be shown on the water thermometer. The main valve of the thermostat will open too late or too early, and the engine will overheat if it is opened too late. If the engine is started too early, the engine warm-up time will be prolonged and the engine temperature will be too low, thus affecting the efficiency.

The thermostat in the vehicle can be checked as follows:

Inspection after starting the engine: Open the radiator filler cap. If the cooling water in the radiator is calm, it means that the thermostat works normally; Otherwise, the thermostat is not working properly. This is because when the water temperature is lower than 70℃, the expansion cylinder of the thermostat is in a contracting state and the main valve is closed. When the water temperature is higher than 80℃, the expansion cylinder expands, the main valve gradually opens, and the circulating water in the radiator begins to flow.

When the temperature indicated by the water thermometer is below 70℃, if there is water flowing through the water inlet pipe of the radiator and the water temperature is warmer, it means that the main valve of the thermostat is not closed tightly and the cooling water circulates prematurely.

Inspection after the water temperature rises: at the initial stage of engine operation, the water temperature rises rapidly; When the water temperature meter indicates 80, the heating rate slows down, indicating that the thermostat is working normally. On the other hand, if the water temperature continues to rise rapidly, when the internal pressure reaches a certain level, the boiling water suddenly overflows, indicating that the main valve is stuck and suddenly opens.

When the water temperature meter indicates 70℃-80℃, open the radiator cover and radiator drain switch, and feel the water temperature by hand. If both are hot, the thermostat works normally. If the water temperature at the radiator inlet is low, there is no water flowing out of the radiator inlet or a small amount of running water, indicating that the main valve of the thermostat cannot be opened.

The temperature controller that is stuck or not closed correctly should be removed, cleaned or repaired, and cannot be used casually.

principle of operation

The main thermostat used is paraffin thermostat. When the cooling temperature is lower than the specified value, the fine paraffin in the thermostat temperature sensor is solid, the thermostat valve closes the passage between the engine and the radiator under the action of the spring, and the cooling liquid returns to the engine through the water pump and circulates in the engine.

When the temperature of the coolant reaches the specified value, paraffin wax begins to melt, gradually becomes liquid, the volume increases, and the rubber tube is compressed and shrunk. When the rubber tube contracts, it generates upward thrust on the push rod, and the push rod generates downward reverse thrust on the valve to open the valve. At this time, the coolant returns to the engine through the radiator and thermostat valve, and then returns to the engine through the water pump for large circulation.

Thermostats are mostly arranged in the water outlet pipe of the cylinder head, which is simple in structure and easy to eliminate bubbles in the cooling system; The disadvantage is that the thermostat is often switched on and off when it works, resulting in oscillation.