Replacing the coolant (BMW 3 Series E21)

Open the interior heater tap by setting the switch handle to the "warm" position and unscrew the expansion tank cap.

Place a container under the engine to drain the fluid, disconnect the drain hose from the radiator and use a 19 mm wrench to unscrew the drain plug with a hex head located at the rear of the cylinder block on the right and drain the fluid.

Pour coolant into the expansion tank.

Start the engine and let it run at fast idle. Loosen the purge screw located next to the diagnostic connector.

Add fluid to the expansion tank until it flows out without bubbles, then tighten the bleed screw.

Wait about 1 minute and stop the engine.

Start the engine again and let it run for about 30 seconds at 4000 rpm.

When the engine is idling, check to see if warm air is entering the passenger compartment.

After the engine has cooled down, add enough fluid to the expansion tank so that its level is no more than 2 cm below the tank cap.

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