When the engine is not warmed up, the main thermostat valve 1 blocks the flow of coolant through the radiator, due to which the engine warms up much faster. Once the coolant temperature reaches a certain value, the main thermostat valve begins to gradually open and the liquid from the radiator flows into the engine. At the same time, additional valve 2 gradually closes the flow of liquid moving in a small circle around the radiator.
The liquid cooled in the radiator is returned to the engine, thereby reducing its temperature. As the engine warms up, the main valve opens wider and wider, and finally the passage from the radiator opens completely and the small circle closes.
The thermostat is equipped with electric heating. In partial load mode, when it is advisable to increase the engine temperature to improve its efficiency, the electric heating is turned off - the thermostat begins to open at 98°C, and opens completely when the coolant reaches a temperature of 102-105°C.
Under heavy engine loads, it is necessary to lower the coolant temperature for normal engine operation. To do this, the ECU turns on the electric heater, and thereby reduces the thermostat opening temperature to the required value, up to 90°C.
If the electric heater fails, the thermostat will ensure engine operation in all modes at elevated temperatures. To eliminate this malfunction, it is necessary to replace the thermostat assembly. Failure of the thermostat itself leads to either engine overheating (if the main thermostat valve does not allow hot coolant to flow into the radiator), or to incomplete/long warming up of the engine to operating temperature (if the main thermostat valve is constantly open).
You can determine that the thermostat is faulty by checking the temperature of the lower radiator hose by touch. When the thermostat is stuck closed, this hose will remain barely warm when the engine is fully warm.
If the thermostat is stuck open, the lower hose will get warmer as the engine warms up, the engine will not warm up in cold weather, and barely warm air will come out of the heater. But there are cases when the thermostat gets stuck in some middle position or it does not open completely.
If there is any doubt about the correct operation of the thermostat, it is necessary to check it. But since this car's thermostat operates at high temperatures, above the boiling point of water, it is too difficult to check it at home. Therefore, it is easier to make sure that it is working properly by replacing it with a new one or one that is known to be working, or by contacting a specialized service station.
The thermostat is installed in a separate housing located on the left side of the cylinder head.
Thermostat: 1 — body; 2 - electric heater; 3 - thermostat cover mounting bolts; 4 - thermostat cover; 5 — hose; 6 — clamp
The thermostat is not repaired. If the test shows that it is faulty, it must be replaced.
Replacing the thermostat
1. We prepare the vehicle for maintenance and repair and install it on an inspection pit or overpass.
2. Drain the coolant
3. By pressing the lock, disconnect the wiring harness block from the thermostat electric heating 2 (see above).
4. Move spring clamp 6 along hose 5 and remove the hose.
5. Using an E10 mm wrench, unscrew the four bolts 3 securing the thermostat cover 4 and remove the cover.
6. Remove the gasket.
7. Remove the thermostat.
8. Clean the mating surfaces.
9. Install a new gasket.
10. Install the parts in the reverse order, tighten the thermostat cover mounting bolts to a torque of 8 Nm.
11. Fill with coolant
12. Start the engine and make sure there are no leaks. If a leak is detected, we eliminate the problem.