Removal and installation, checking of the thermostat (BMW 5 Series E34)

As the engine warms up, the thermostat opens a large cooling circuit. If the thermostat fails, the engine overheats. This is determined by the increased temperature readings on the temperature gauge while the radiator remains cold. But a thermostat defect can also manifest itself in the fact that it remains open even after the liquid has cooled. This is determined by the fact that the engine does not warm up to its operating temperature or the temperature gauge needle deflects more slowly than before or in winter the heating power is insufficient.

Caution: If the engine overheats after a short distance, the cause may be limescale deposits in the radiator.

Removal

Disconnect the ground wire from the battery.

Caution: When the battery is disconnected, the information in the electronic memory devices, such as the engine fault memory or the radio security code memory, is erased. When disconnecting the battery, follow the instructions in the section "Removal and installation the battery".

Drain some of the coolant from the engine into a container.



Unscrew the thermostat housing cover.

Note: On diesel engines, as well as on the M50 engine, the bolts have different lengths, so to make installation easier, it is better to mark the position of the bolts. In addition, on the M50 engine, the engine suspension bar must first be unscrewed.

Mark the position of the thermostat and remove the thermostat.

Examination

Heat the thermostat in a water bath. The thermostat should not touch the walls of the vessel. Monitor the temperature with an appropriate thermometer.

At a temperature of approximately 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. If there are any deviations, replace the thermostat.

Installation

Clean the contact surfaces on the body and cover.



Insert thermostat 7 with a new gasket, bracket facing out.





Engine M50 (Four valve engine): Install the thermostat so that the arrow on it points upward. On the M51 diesel engine, the air outlet hole should point upward.

Insert a new O-ring 8 into the thermostat (Figure W - 1820).

Put on cover 9 and tighten bolts 11 evenly to a torque of 9 Nm.

Attention: Do not overtighten the screws; on the M50 engine, do not forget to install the bar.

Fill the engine with coolant and bleed air from the cooling system.

Connect the ground wire to the battery.

Warm up the engine until the viscous coupling fan turns on. Check if the lower part of the radiator is warm and if the thermostat housing is sealed. If necessary, tighten the bolts slightly.