Caution: If the engine overheats after a short trip, the cause may be lime deposits in the radiator.
Withdrawal
Remove fan shroud.
Drain some of the coolant into a container. Models 316i, 318i, 318tds, 325td/tds:
Attention: On models 316i, 318i manufactured since September 1993, the thermostat is firmly built into the housing and therefore cannot be removed.
Drawing W 10176
4 Thermostat housing
5. Air release bolt
6. Thermostat
7. O-ring
10. Bolt
Models 318 is/ti:
1. O-ring
2. Gasket
Models 3201, 325i, 328i:
4. Connecting flange
5. Thermostat
6. O-ring
7. Gasket
8. Bolt M6
9. Bolt M8
Unscrew the cover of the thermostat housing (from the front of the engine).
Attention: On a six-cylinder petrol engine, the bolts have different lengths, so to facilitate subsequent installation, mark the location of the bolts. In addition, you must first remove the suspension bar.
Mark the installation position of the thermostat and remove 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.
Models 320i, 325i, 328i: Install the thermostat with the arrow pointing up, see illustration.
Models 318is/ti, 318tds, 325td/tds: Install the thermostat so that the air outlet is at the top, see drawing W 1843.
Lubricate the new O-ring of the thermostat lightly with glycerine and insert it, see the figures in the subsection "Withdrawal".
Models 318is/ti, 320i, 325i, 328i: Be sure to replace the paper gasket.
Position the thermostat housing and tighten the bolts evenly to 10 Nm.
Attention: Do not overtighten the bolts. On models 3201, 3251 do not forget to put the suspension bar. Suspension rail bolts (M8 thread) tighten with a torque of 20 Nm.
Install fan shroud.
Fill with coolant and bleed air from the cooling system.
Warm up the engine until the viscous fan clutch engages. If there are leaks, tighten the bolts a little.