Removal and installation / checking the thermostat (BMW 5 Series E39)

As the engine temperature rises, the thermostat opens a large circuit of coolant circulation. If the thermostat remains closed due to a fault, the engine overheats. This can be determined by the coolant temperature gauge moving into the red area, while the radiator of the cooling system remains cold. A faulty thermostat can also remain open after the coolant has cooled. In this case, the engine does not reach its operating temperature, the coolant temperature gauge rises more slowly than before, and in winter, the heating efficiency of the heater is low.

Caution: If the engine becomes hot after the car has been driven for a short distance, the cause may be low efficiency of the radiator due to salt deposits in it.

Removal

Remove the fan, see page 38.

Drain some coolant into a suitable container, see section "Maintenance work".





Loosen the clamps and disconnect from the thermostat housing (from the front side of the cylinder block) coolant hoses.





Models 520i, 523i, 528i: Unscrew the engine suspension eye fastening. Unfasten and remove the cable management box, see figure.

Unscrew the thermostat housing cover fastener.

Note: The mounting bolts are of different lengths, so to facilitate subsequent assembly, the bolt positions should be recorded.

Mark the mounting position of the thermostat and remove it.

Examination

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

At a temperature of approximately +88°C, the thermostat valve begins to open. The temperature at which the valve begins to open is stamped on the thermostat.

Check if the thermostat valve opens and closes again and if the valve opening temperature corresponds to the value stamped on the thermostat. Replace the thermostat if necessary.

Installation

Clean the contact surfaces of the housing and cover.



Models 520i, 523i, 528i: Insert the thermostat into the cylinder head so that the arrow stamped on it points upward, see illustration.



Models 525tds: Insert the thermostat so that the air bleed plug is at the top. When the lid is attached, it is located in the recess in the lid.

The new thermostat sealing ring is easy to lubricate with glycerin and install, see the pictures above.

Models 520i, 523i, 528i: Always replace the paper seal.

Insert the thermostat housing and tighten the mounting bolts evenly to a torque of 10 Nm.

Note: Do not tighten the bolts too much. For a 6-cylinder petrol engine, do not forget to screw on the lifting eye. Tighten the M8 bolts securing the lifting eye to 20 Nm.

Secure the box for laying wires with clamps.

Install the fan and fan shroud.

Top up the coolant level and bleed the cooling system, see section "Maintenance work".

Warm up the engine until the viscous coupling engages the fan. Check if the radiator is heating up at the bottom and if the thermostat housing is tight. If leaks are detected, tighten the housing mounting bolts slightly.

The original text can be read on the website «BMWMAN.ru»