Loosen the hex head plug from the engine block.
Remove the radiator filler cap.
Note. When draining the coolant, the handle of the heater tap control switch on the dashboard must be in the position «Warm» («Warm»).
Set the heater tap control switch (left handle) into position «Warm» («Warm»).
Fill the radiator expansion tank with fluid.
BMW «525», «528»
Loosen the bleed valve (headless screw), located on the thermostat housing and fill the system with liquid through the expansion tank.
After the liquid with air bubbles has stopped coming out through the bleed screw, tighten the screw.
Fill the expansion tank to the mark. Install the radiator cap.
BMW «518», «520», «520i»
Slowly fill the radiator through the filler neck.
Replace the radiator cap.
Start the engine and warm it up at a crankshaft speed of 2000-2500 rpm.
Stop the engine.
After about 1 minute, start the engine again.
Let it run for 30 seconds at a speed of at least 4000 rpm.
Make sure that when the engine is idling, a stream of warm air comes out of the switched on heater.
Cool the engine (up to the position of the pointer arrow between the two white marks).
Add fluid to the radiator to a level of at least 2 cm below the plug. Excess fluid will be immediately removed through the overflow plug.