Removal and installation, checking of the thermostat (BMW 3 Series E30)

As the engine warms up, the thermostat opens a large cooling circuit. If the thermostat fails, the engine overheats. This is determined by the temperature readings on the temperature gauge: it is elevated, while the radiator remains cold. But a thermostat defect can also manifest itself in the fact that it remains open 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 moves 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.

Four-cylinder engine

Removal

Disconnect the ground wire from the battery.

Drain the coolant from the engine into a container.

Completely release clamps "1", "2" and "4" and move them back.



Disconnect the water hoses and remove thermostat "3".

Examination



Using a steel ruler or calipers, measure the position of thermostat "1" in the housing relative to the edge of the lower fitting "2" and record the result as dimension "a".



Heat the thermostat in a water bath. Monitor the temperature with a suitable thermometer.

At a temperature of approximately 80°—88°C, the bimetallic spring "3" of the thermostat begins to expand. Measure the position of the thermostat after exceeding the opening temperature, i.e. dimension "b". Dimension "b" must be greater than dimension "a", otherwise replace the thermostat. The opening temperature is engraved on the thermostat.

The thermostat reaches its maximum opening at approximately 95°C. When the temperature of full opening is reached, measure the position of the thermostat. The size should be 8±1 mm larger than the size "b", i.e. "b" - "a" = 8±1 mm.

Installation

Insert the thermostat.

Fill with coolant (see section "Replacing the coolant").

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.

Six-cylinder engine

Removal

Disconnect the ground wire from the battery.

Drain some coolant from the engine into a container.



Unscrew the thermostat housing cover (arrows).



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 the thermostat with the new gasket, bracket facing out.

Replace the cap and tighten evenly to 9 Nm.

Caution: Do not overtighten the screws.

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.