Attention! Do not open the cap of the expansion tank and do not remove the thermostat until the engine has completely cooled down! See also Section 2.
General information
1. The thermostat is designed to speed up the engine warm-up process and divides the cooling system into two circuits: large and small. Until the coolant temperature reaches a certain value (as a rule, thermostats are adjusted to the temperature 80-90°C) the thermostat valve is closed and the liquid circulates through the small circuit without entering the radiator. As a result, the engine quickly warms up to normal operating temperature. When a certain threshold value of the coolant temperature is exceeded, the thermostat filler begins to expand and opens the valve - the liquid begins to circulate through a large circuit through the radiator.
2. The thermostat housing is attached to the engine. The location of the thermostat may vary depending on the layout of the powertrain, but it is easy to find - it is always connected to the upper radiator hose.
3. Below is a detailed description of the procedure for removing / installing the thermostat on Z16XE / Z18XE engines for other engines, we will give only the differences and features.
Removal / installation
Engines Z16XE/Z18XE
4. Drain the coolant (see Section 3).
Note: It is not necessary to drain the coolant completely. It is enough that the coolant level drops below the thermostat housing.
5. Remove the engine cover (see chapter 2) and, loosening the fastening clamp, disconnect the upper hose of the cooling system from the thermostat housing.
6. Disconnect the hose (see resist. illustration) cooling system, disconnect the connector of the electrical wiring of the coolant temperature sensor, unscrew the 2 fixing bolts (on the Z16XE engine - 3 bolts) and remove the thermostat housing from the engine.
9.6 Hull (4) thermostat (on the example of the Z18XE engine) - the arrows indicate the mounting bolts: 2. Coolant hose; 3. Wiring connector for coolant temperature sensor
7. Check thermostat (see below if necessary thermostat together with housing. When replacing, do not forget to reinstall the coolant temperature sensor in the new thermostat housing, tighten it with the required force (see specs).
8. Installation is made in an order the return to an order of removal. Replace gasket before installation (see resist. illustration) thermostat and tighten the bolts securing the thermostat housing with the required force.
9.8 Replace thermostat seal before installation
9. Fill the system with coolant (see Section 3).
10. Start engine, warm up to operating temperature and check for leaks.
Features of the Z19DT engine
11. Remove cooler (see resist. illustration) exhaust gas recirculation systems.
9.11 Elements of the cooling system for Z19DT engines (H): 1. Thermostat housing; 2. Branch pipe of the cooling system; 3. Water pump; 4. Heat exchanger; 5. EGR cooler
12. Disconnect 3 hoses of the cooling system from the thermostat housing.
Features of the Z19DTH engine
14. Remove the battery (see chapter 5).
15. Separate the preheater control device and carefully move it aside.
16. Loosen the cooling system pipe and disconnect 4 hoses from the thermostat housing.
Features of Y20DTH/Y22DTR engines
17. Remove turbocharger hose (see illustration 7.27).
18. Disconnect the preheat hose from the turbocharger to the regeneration valve and move it aside.
19. Turn out 4 fixing bolts and remove the case (see resist. illustration) thermostat, and if necessary, the coolant temperature sensor.
9.19 Hull (1) thermostat and sensor (2) coolant temperature (motors Y20DTH/Y22DTR)
Features of the Z20NET engine
20. When draining the coolant, unscrew the drain plug located at the bottom of the water pump (see resist. illustration).
9.20 Drain plug (arrow) water pump (Z20NET engine)
21. Remove the air cleaner (see chapter 4) and remove the vacuum pump.
22. Remove 3 bolts (see resist. illustration) fasteners and remove the thermostat housing.
9.22 Housing bolts (1) thermostat (Z20NET engine) the arrow indicates the position of the third bolt
23. Installation is made in an order, the return to an order of removal. Remember to replace the vacuum pump seal, before screwing in the water pump drain plug, wrap its threads with Teflon tape or lubricate with sealant.
Features of Z22SE/ Z22YH engines
24. When draining the coolant, unscrew the drain plug located at the bottom of the water pump (see illustration 9.20).
25. Loosen clamp (see resist. illustration) fasteners and disconnect the hose from the thermostat housing. Turn out 2 fixing bolts and remove the case of the thermostat from the engine.
9.25 Bolts (2) thermostat housing fasteners and mounting clamp (1) coolant hose (engines Z22SE/Z22YH)
26. Installation is made in an order, the return to an order of removal. Remember to replace the thermostat seal by lightly lubricating it with silicone grease (white color). Before screwing in the drain plug of the water pump, wrap its threads with Teflon tape or lubricate with sealant.-
Examination
27. The main reason for the failure of the thermostat is the aging of the filler and the loss of its ability to significantly change its volume depending on temperature. During operation, mechanical damage to the thermostat valve may also occur.
28. Preliminarily, the thermostat can be checked without removing it from the engine. With the engine running, open the hood and touch the upper radiator hose.
Attention! Be careful - at a high temperature of the coolant, you can burn your hand!
If the engine has just started and has not had time to reach operating temperature, and the liquid in the upper hose is already warm, then the thermostat valve is not closed. This is also indicated by a slower than usual increase in the temperature of the coolant, and in winter - a decrease in the heater power. If the indicator lamp is activated (see chapter «Controls and methods of operation», Section 16) coolant temperature on the instrument panel, and the upper pipe is cold - it is guaranteed that the valve does not open a large circuit.
Note: This is only an approximate way to check, and you need to be sure that all other components of the cooling system and temperature control are functioning properly, the coolant level is normal.
Follow the recommendations in the section on diagnosing problems with the cooling system.
29. The most accurate results are obtained by checking the thermostat on a workbench.
30. Remove the thermostat from the engine (see above).
31. Tie a piece of wire to the thermostat assembly and lower it into a container filled with water (see resist. illustration). Put the thermometer in there.
9.31 Checking the correct operation of the thermostat
Attention! Make sure that the thermometer and thermostat do not come into contact with the walls and bottom of the container
32. Start slowly heating the water, watching the change in the thermometer readings. The actuation of the thermostat valve must be in exact accordance with the control settings for the specific engine model (see specs).
9.33 Checking that the thermostatic valve is fully open
33. Estimate the value of the full opening of the valve, - the nominal value is b-a \u003d 8 mm (see resist. illustration). If abnormal, replace the thermostat.
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