When checking the thermostat on a car after starting a cold engine, the inlet and outlet hoses of the radiator of the cooling system should remain cold for some time.
At the same time, the thermostat valve remains closed, and the coolant circulates in a small circle, bypassing the radiator.
Once the fluid temperature reaches 87°C, the radiator hoses should begin to heat up rapidly, indicating that the coolant has begun to circulate in a large circle.
For greater clarity, we show the work on a dismantled engine.
Removing the timing belt (see Checking the condition and replacing the timing belt).
Remove the rear cover of the timing gear (see Removing the coolant pump).
With a head or a "12" key, we unscrew the two bolts securing the exhaust pipe of the cylinder head.
Move the pipe to the side (the hose can not be disconnected from the nozzle).
We take out the thermostat from the nest in the cylinder head.
Remove the rubber gasket from the thermostat.
If the gasket is damaged or has lost elasticity, it must be replaced with a new one.
To check the thermostat, lower it into a vessel with water.
We heat the vessel, while stirring the water and controlling the beginning of the opening of the valve with a thermometer.
The valve stem should begin to retract at 87°C..
... which is indicated on the thermostat flange.
At a temperature of 102°C, the valve should open fully - stroke of at least 8 mm.
Install the thermostat in reverse order.