Do not remove the radiator cap, drain the coolant, or replace the thermostat before the engine is completely cool.
Examination
1. Before concluding that the thermostat is the cause of a malfunction in the cooling system, check the coolant level, drive belt tension and the meter is working (or signal lamp) cooler temperature.
2. If there are suspicions that the engine warms up too slowly (based on poor heater performance or temperature readings), It is possible that the thermostat is stuck open. Replace thermostat.
3. If the engine overheats during operation, feel the upper radiator hose with your hand. If the hose is not hot and the engine is overheated, then the thermostat may be stuck closed, preventing coolant from circulating through the radiator. Replace thermostat.
Do not operate the vehicle without a thermostat. The engine will warm up slowly in cold weather, resulting in wasteful fuel consumption and poor vehicle handling. Usually a new thermostat is not an expensive component.
4. If the upper radiator hose is hot, coolant is circulating through the radiator and the thermostat is at least partially open. Please refer to the section for information Diagnosis of malfunctions of the cooling system at the end of this Section to identify the causes of overheating.
Replacement
All models
1. Disconnect the negative battery cable.
If your car's radio is equipped with an anti-theft system, make sure you have entered the correct code before disconnecting the battery.
If, after connecting the battery, the inscriptions on the instrument panel appear in the wrong language, refer to Section Anti-theft audio system and instrument panel language, for instructions on how to set the desired language.
2. Drain the cooling system (see chapter Car maintenance). If the coolant is relatively new or in good condition, do not discard it and then use it again.
M10 engines
1. The thermostat is located in the lower hose. Remove the cooling fan first.
2. Note the position of the thermostat, then unscrew the hose clamps and remove the thermostat from the hose connections. On M10 engines (four-cylinder) thermostat (indicated by an arrow) built into the radiator hose
3. Install the thermostat in the hose connection and tighten the hose clamps.
4. Install the cooling fan.
M20 and M30 engines
1. Loosen the hose clamp -A, then disconnect the hose (hoses) from the thermostat cover. Please note that the coolant temperature sensor (which is almost invisible due to the fuel pressure regulator) located at the top of the thermostat housing -B.
2. If the outer surface of the fitting that mates with the hose is damaged in any way (corrosion, mechanically, etc.), its condition may be worsened by removing the hose. If so, you will need a new thermostat housing cover.
3. Give bolts and disconnect a cover of a casing. If she is stuck, tap her with a soft-faced hammer. Be prepared for the fact that after the destruction of the gasket sealant, a little coolant may splash out.
4. Note the correct position of the thermostat and remove it.
5. Plug the opening in the engine with a rag, then remove all traces of the old gasket material (if it's paper). Otherwise, remove the rubber o-ring and remove the sealant from the housing and cover with a special scraper.
6. Remove a rag from the hole in the engine and clean the mating surfaces of the gasket.
7. Install the new thermostat and gasket into the housing. Make sure that the installation is correct - the end of the spring should be directed towards the engine.
8. Install the cover and fit the bolts. Tighten the bolts to the required torque.
M40 engines
1. Remove the cooling fan and timing belt top cover.
2. Unscrew the hose clamp and remove the lower hose from the elbow on the front side of the cylinder head.
3. Unbolt the knee from the cylinder head.
4. Note the correct position of the thermostat, then remove it.
5. Remove the rubber o-ring; assembly requires a new one.
6. Place the thermostat in the cylinder head in the same position as it was before removal (arrow pointing up).
7. Press a new O-ring into the groove and install the elbow onto the cylinder head. Tighten the bolts.
8. Connect the lower hose to the elbow and tighten the hose clamp.
9. Install the timing belt top cover and cooling fan.
All models
1. Fill the cooling system (see chapter Car maintenance).
2. Connect the negative battery cable.
3. Start the engine, warm it up to normal operating temperature, then check for leaks and check that the thermostat is working properly (as described earlier in this Section).