Symptom | Reason / Features |
A.The temperature, according to the readings of the device, slowly increases, the operating temperature is reached very slowly, the heating is weak. | Thermostat valve poppet stuck open (for example, due to scale); access to the radiator remains permanently open. The engine has been running cold for too long. Although this may not lead to serious malfunctions in a short time, it is still necessary to replace the thermostat as soon as possible. |
B.The temperature, according to the readings of the device, is close to boiling or the signal light is on despite the normal level of the coolant. Radiator and lower radiator hose are cold. | Thermostat valve poppet blocked (for example, due to leakage of the walls of the thermosensitive filler cup). Do not continue driving under any circumstances, as this could cause serious damage due to overheating of the engine! Replace thermostat. |
Note. Recommendation: if the engine overheats on the road due to a faulty thermostat, you can only move on in tow or after replacing the thermostat. If you decide to replace, then wait until the coolant has cooled down. Find a suitable container for draining the coolant. If the container could not be found, you can pour clean water into the cooling system for a while. However, do not forget to bring the concentration of antifreeze additive to normal as soon as possible!