Attention: If the coolant is drained during repair work, it should be drained into a vessel, since it has not yet lost its frost protection and anti-corrosion properties.
Coolant drain
Disconnect the ground wire from the battery.
Set the heater switch in the passenger compartment to maximum heating power.
When opening the cap, first unscrew it a little to release the pressure. Then fully unscrew and remove the cover.
Caution: When the engine is hot, open the cover carefully. Danger of injury! When opening, put a rag. If possible, open the cap when the coolant temperature is below 90°C.
Remove the plastic lining under the radiator.
Place a clean vessel under the radiator and unscrew the drain plug -1- of the radiator.
Place a clean container under the engine and unscrew the drain plug -2- on the engine block.
Models 316i from September 1988 and 318i from September 1987: if only the radiator needs to be drained, open the vent plug at the top of the radiator. In this case, it is not necessary to unscrew the drain plug on the motor unit.
Drain the coolant completely.
Screw the plug with a new gasket on the motor block and tighten it to 50 Nm.
Tighten the drain plug on the radiator slightly. To do this, insert a coin into the slot of the plug and tighten the plug by hand.
Coolant filling
Four-cylinder engine manufactured before August 1988: Fill in coolant to a level 2 cm below the threaded part of the neck -1-. Leave the neck open for now.
Models 316i from September 1988 and 318i from September 1987: open the vent bolts -1- on the thermostat housing and -2- on the radiator.
Pour coolant into the expansion tank until the tank is completely filled and until coolant free of air bubbles flows out through both vent bolts.
Tighten the vent bolts and expansion tank cap.
Start and warm up the engine above 2500 rpm. Remaining air in the cooling system will cause the coolant level to drop to approximately the prescribed mark. A slight excess of the level, up to about the 9th rib from the top, is permissible.
Six-cylinder engine: Pour coolant into the expansion tank up to the -K- mark. Close the bottle cap.
Connect ground wire to battery.
Warm up the engine until the thermostat opens (bottom water hose gets warm). At the same time give jerks gas. Pre-August 1988 4-cylinder engine: coolant may need to be topped up during warm-up. Finally, close the cap on the expansion tank.
Six-cylinder engine: bleed the cooling system. To do this, leave the engine running at about 1500 rpm. Open the bleed screw -E- on the thermostat housing and do not close until coolant free of air bubbles flows out through the screw. Then tighten the bolt to 8 Nm.
Check the tightness of the cooling system, especially at the plugs and the water pump.