Checking the thermostat operation (VAZ-2109)

The thermostat must be checked for the temperature at which the main valve starts to open and its stroke. To do this, install the thermostat on a stand in a tank with technical glycerin. Rest the indicator leg bracket against the main valve from below.

Heat glycerin from 78...80°C gradually, increasing the temperature by 1°C per minute with constant stirring so that it is the same throughout the volume.

The temperature at which the valve opens by 0.1 mm is taken as the temperature at which the main valve begins to open. For a serviceable thermostat, the temperature at which the main valve begins to open should be 85...89°C, and the valve stroke should be at least 8 mm when the temperature rises to 102°C.

The simplest check of the thermostat's serviceability can be carried out by touch directly on the car. After starting a cold engine with a serviceable thermostat, the lower radiator hose should heat up when the coolant temperature reaches 87...92°C. In this case, the coolant temperature indicator needle will not reach the beginning of the red zone of the scale by 3...4 mm.