At the thermostat, it is necessary to check the temperature of the beginning of the opening of the main valve and the stroke of the main valve. To do this, the thermostat is lowered into a tank with water or coolant and fixed on a bracket. From below, the indicator leg bracket rests against the main valve.
The initial temperature of the liquid in the tank should be 73-75°C. The temperature of the liquid is gradually increased, by about 1°C for 1 min with constant stirring, so that it is the same throughout the volume.
The temperature at which the main valve stroke is 0.1 mm is taken as the temperature at which the valve opens. The thermostat must be replaced if the opening temperature of the main valve is not within 81°C or the valve stroke is less than 6.0 mm.
The simplest check can be carried out by touch directly in the car. After starting a cold engine with a working thermostat, the lower radiator tank should heat up when the needle of the liquid temperature gauge is approximately 3-4 mm from the tap zone of the scale, which corresponds to 80-85°C.