When checking the thermostat on a vehicle after starting a cold engine, the lower hose that comes off the radiator should remain cold for a while. The thermostat valve is closed, and the fluid circulates in the small circuit, bypassing the radiator. After the fluid temperature reaches 87°C, the lower radiator hose should begin to heat up quickly, indicating that the coolant has begun to circulate in the large circuit.
Drain the liquid from the engine cooling system (see Replacing the coolant).
Using sliding pliers, squeeze the ends of the clamp securing the radiator supply hose and slide the clamp along the hose.
We remove the hose from the thermostat cover branch pipe.
Using pliers, squeeze the ends of the clamp securing the hose for supplying fluid to the throttle heating unit and slide the clamp along the hose.
We remove the hose from the thermostat housing fitting.
Using a 12 mm socket head, unscrew the two bolts securing the thermostat housing to the cylinder head.
We remove the housing with the thermostat cover.
Remove the cover from the thermostat housing.
We remove the thermostat from the housing.
We remove the rubber gasket from the thermostat.
The connection between the thermostat housing and the cylinder head is sealed with a rubber ring.
If the gasket and sealing ring are damaged or have lost elasticity, they must be replaced with new ones.
To check the thermostat, lower it into a vessel with coolant. Heat the vessel, stirring the liquid at the same time and monitoring the start of the valve opening with a thermometer. The valve stem should start to extend at a temperature of 87°C…
…which is indicated on the thermostat flange.
At a liquid temperature of 102°C, the valve should be fully open - the stem stroke should be at least 7 mm.
When installing a thermostat…
…we insert it into the case, orienting it as shown in the photo.
We install the thermostat in the reverse order.
We fill the cooling system with liquid.