How to Check the Thermostat?
3 Answers
After starting the engine, open the radiator cap. If the coolant inside the radiator is calm, it indicates that the thermostat is functioning properly. Otherwise, the thermostat is malfunctioning. There are several criteria to check: 1. When the temperature gauge indicates below 70°C: If there is water flow inside the radiator and the water temperature is warm, it means the main valve of the thermostat is not tightly closed, causing the coolant to prematurely enter the large circulation and resulting in a slow rise in water temperature. In the initial stage of engine operation, if the water temperature rises quickly and slows down after the temperature gauge indicates 80°C, it means the thermostat is working normally. Conversely, if the water temperature continues to rise rapidly and reaches an alarm state, it indicates that the thermostat is damaged. 2. When the temperature gauge indicates between 70°C and 80°C: If the water temperature at the radiator filler port is low, and there is little or no water flow at the inlet pipe of the upper radiator chamber, it means the main valve of the thermostat cannot open. Under normal circumstances, the temperature difference between the upper and lower radiator hoses should not be too large.
I've been driving for over 20 years and have encountered thermostat issues several times. First, make sure the engine is completely cooled down, otherwise it's dangerous to touch hot components. After starting the car, I usually feel the radiator's outlet and inlet hoses with my hand. If there's a temperature difference - like the outlet hose stays cold while the inlet hose gets hot - it likely means the thermostat is stuck closed. I'll insert a small thermometer into the outlet to check the temperature; it should maintain around 90°C to be normal. Any reading significantly higher or lower indicates a problem. Another method is to drive for a while and observe the temperature gauge - if it rises too quickly or doesn't move at all, that's a clear fault signal. A faulty thermostat can cause engine overheating and damage components, leading to expensive repairs. I remember once before a long trip when I didn't check it, and my engine ended up smoking and breaking down halfway - I regretted it so much. My advice is to routinely inspect it during regular maintenance, safety always comes first.
As a young car enthusiast who loves DIY maintenance, here are some simple tips for checking the thermostat. Before starting the engine, make sure the cooling system is empty to avoid accidents. After idling for a few minutes, I put on gloves and feel the temperature of the upper and lower radiator hoses; if there's a significant difference, suspect thermostat failure. Alternatively, if the temperature gauge shows abnormally high readings, shut off the engine immediately. If you don't want to spend too much money, buy an inexpensive thermometer to measure the outlet temperature—it should normally be between 85-95°C. Common causes of a stuck thermostat include dirt buildup or aging. If it's malfunctioning, you can try replacing it yourself, but don't force it and damage the gasket. Also, keep the coolant clean and change it regularly to prevent deposits, or else engine overheating and cylinder damage could become serious issues. Doing these checks regularly saves on repair shop costs and time—it's quite practical.
