Caution: If the engine becomes hot after the vehicle has been driven for a short distance, the cause may be the low efficiency of the radiator as a result of salt deposits in the radiator.
Withdrawal
Remove the fan, see p. 38.
Drain some coolant into a suitable container, see section "Maintenance work".
Model 525tds
4 - thermostat housing
5- air removal plug
6 - thermostat
7 - sealing ring
10 - hex bolt
Models 520i, 523i, 528i
4 - thermostat housing
5 - thermostat
6 - sealing ring
7 - sealing gasket
8 - hex bolt M6
9 - hex bolt M8
Loosen the clamps and disconnect from the thermostat housing (from the front side of the cylinder block) coolant hoses.
Models 520i, 523i, 528i: Loosen the engine lifting eye. Loosen and remove the cable management box, see illustration.
Loosen the thermostat housing cover.
Attention: The fastening bolts have different lengths, therefore, to facilitate subsequent assembly, the positions of the bolts should be recorded.
Mark the installation position of the thermostat and remove it.
Examination
Heat the thermostat in a water bath. In this case, the thermostat should not touch the walls of the vessel. Control the heating temperature with a suitable thermometer.
At a temperature of approximately +88°C, the thermostat valve starts to open. The valve opening start temperature is stamped on the thermostat.
Check if the thermostat valve opens and closes again and that the temperature at which the valve starts to open corresponds to the value entered on the thermostat. Replace 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 upwards, see illustration.
Models 525tds: Insert the thermostat so that the bleed plug is at the top. When the lid is attached, it is located in the recess of the lid.
The new thermostat o-ring is easy to lubricate with glycerin and install, see the pictures above.
Models 520i, 523i, 528i: Always replace the paper seal.
Insert thermostat housing and tighten bolts evenly to 10 Nm.
Attention: Do not overtighten the bolts. For a 6-cylinder petrol engine, do not forget to screw on the hanging eye. Tighten the eye bolts M8 to 20 Nm.
Fasten the cable management box with clips.
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 turns on the fan. Check whether the radiator heats up in the lower part and whether the thermostat housing is sealed. If leaks are found, slightly tighten the housing fixing bolts.