Attention! Do not open the radiator cap and do not remove the thermostat until the engine has completely cooled down! See also the warning at the beginning of the Section Antifreeze - general information.
Examination
1. Before finally establishing your opinion about the failure of the thermostat, check the coolant level in the system, the condition and tension of the drive belt (see chapter Settings and ongoing maintenance), as well as the correct functioning of the temperature meter / control lamp.
2. One of the possible reasons for the engine warming up too slowly (according to meter readings) is the thermostat sticking in the open position. Replace the thermostat with a new one.
3. If the engine overheats, feel the lower radiator hose with your hand. If the hose is not hot, the thermostat may be stuck closed, cutting off coolant circulation through the radiator. Replace thermostat.
Attention! In no case do not operate the car with the thermostat removed - this may break the feedback of the on-board processor, which will lead to an increase in the toxicity of exhaust gases and an excessive increase in fuel consumption.
4. If the lower hose is hot, this means that the coolant is properly circulating through the radiator, i.e. thermostat is open. Refer to the materials of the Section devoted to the diagnosis of malfunctions of the cooling system.
5. The most accurate results are obtained by checking the thermostat on a workbench.
6. Remove the thermostat from the engine (see chapter Engine).
7. Tie a piece of wire to the thermostat assembly and lower it into a container filled with water. Put the thermometer in there.
Attention! Make sure that the thermometer and thermostat do not come into contact with the walls and bottom of the container.
8. Start slowly heating the water, watching the change in the thermometer readings - the thermostat valve should actuate exactly in accordance with the requirements Specifications.
9. Estimate the value of the full opening of the valve, - the nominal value is 8 mm.
10. A description of the procedures for removing and installing the thermostat is given in Section Removal and installation of the thermostat.