Caution: If the engine overheats after a short trip, the cause may be lime deposits in the radiator.
Withdrawal
Disconnect the ground wire from the battery.
Attention: When the battery is disconnected, the information in the electronic memory devices, such as the engine trouble memory or the radio security code memory, is erased. When disconnecting the battery, follow the instructions in section "Removing and installing the battery".
Drain some of the coolant from the engine into a container.
Unscrew the thermostat housing cover.
Attention: On diesel engines, as well as on the M50 engine, the bolts have different lengths, therefore, to facilitate installation, it is better to mark the position of the bolts. Also, on the M50 engine, you must first unscrew the engine mount bar.
Mark the position of the thermostat and pull out the thermostat.
Examination
Warm up the thermostat in a water bath. The thermostat must not touch the walls of the vessel. Control the temperature with an appropriate thermometer.
At a temperature of about 80°C, the bimetallic spring of the thermostat begins to expand. The thermostat reaches its maximum opening at approximately 95°C.
Check the opening and closing of the thermostat and the compliance of the opening temperature with the value engraved on the thermostat housing. In case of deviations, replace the thermostat.
Installation
Clean the contact surfaces on the housing and on the cover.
1 thermostat housing
2 Cork
3 Copper O-ring (parts 2 and 3 are often missing)
4 Housing gasket
5 Spring washer
6 Nut
7 Thermostat
8 Ring
9 Lid
10 Screw release valve
11 Bolt
12 Temperature gauge sensor
13 O-ring
14 Temperature sensor
Insert thermostat 7 with the new gasket clip outward.
M50 engine (Four valve engine): Position the thermostat so that the arrow on it points upwards. On the M51 diesel engine, the air outlet should be facing up.
Insert a new O-ring 8 into the thermostat (Figure W - 1820).
Put on cover 9 and evenly tighten bolts 11 to a torque of 9 Nm.
Attention: Do not overtighten the screws, do not forget to set the bar on the M50 engine.
Fill the engine with coolant and bleed air from the cooling system.
Connect ground wire to battery.
Warm up the engine until the fan is turned on by the viscous coupling. Check if the lower part of the radiator is warm and if the thermostat housing is tight. Tighten screws slightly if necessary.