1. Circulation in a small circuit (temperature up to +87°C) – the thermostat is closed. The bypass valve directs the coolant to the pump. From there, the liquid is fed back to the engine. This mode is used to quickly warm up the engine.
2. Mixed mode (temperature +87...+102°C) – the thermostat opens. The liquid, circulating along the small circuit, partially passes through the radiator.
3. Circulation along a large circuit (temperature over +102°C) – the thermostat is fully open. All liquid passes through the radiator.
Removal and checking the thermostat
If the thermostat gets stuck, it can cause major damage to the engine. The fluid will boil and evaporate quickly. In this case, you cannot continue driving. Tow the car to a repair shop. Removing and installing the thermostat is not a difficult job. When buying a new thermostat, do not forget new gaskets, including the housing gasket. You will also need a container to drain the fluid. Remove the thermostat only on a cold engine. Different models have slightly different thermostat housings in location.
Sequence of works
1. Disconnect the cable from the negative terminal of the battery.
2. Drain the coolant as described previously.
3. Remove the front upper engine cover.
4. Loosen the clamp and disconnect the radiator hose from the thermostat housing.
5. Disconnect the small hose from the expansion tank (having previously loosened the clamp).
Fig. 4.47. Thermostat location: 1 – thermostat housing; 2 – coolant pump; 3 – chain tensioner; 4 – exhaust manifold
(Original published on the website: mercedesman.ru)
Fig. 4.48. Coolant pump in the block with thermostat: 1 – V-belt pulley flange; 2 – pump body; 3 – pump impeller; 4 – radiator hose nipple; 5 – thermostat housing; 6 – thermostat; A - from the radiator; B - from the engine; C - to the engine
6. Unscrew the thermostat housing and remove it together (Fig. 4.47). The thermostat is assembled with the water pump (Fig. 4.48).
Fig. 4.49. Checking the thermostat
7. Place the thermostat in a container with water (Fig. 4.49) and check the operating temperature by slowly heating the water. For a thermostat that has already been in operation, a difference in operating temperature of ±3°C is permissible.
8. Check that the valve is completely closed when cooling.
9. If it is not working properly, replace the thermostat. On 4- and 6-cylinder engines, the thermostat is a one-piece design.
10. Before installing the thermostat, clean the connection points with the gasket on the housing and engine.
11. Install the housing with the thermostat and a new gasket and tighten to a torque of 10 Nm.
12. Connect the radiator hose, making sure it is seated correctly and the clamp is securely tightened.
13. Fill with coolant.
14. Connect the cable to the negative terminal of the battery.
15. Warm up the engine and make sure that the radiator is hot at the bottom.
16. Check the tightness of the thermostat installation.