The BMW E34 uses a bleed screw to remove air from the cooling system. While some vehicles use a bottom radiator hose or the radiator cap itself for this job, BMW has chosen this simpler method to bleed the system of air. There are two types of E34 radiators: one with a radiator-mounted expansion tank and one with a separate tank. How you bleed the system will vary slightly according to your specific set-up, but in principle the procedure is the same.
Place the catch pan underneath the radiator.
Place your key in the ignition and start the E34's engine.
Open the bonnet. Locate the bleeder screw on top of the expansion tank, which is mounted atop the radiator. Turn the screw counterclockwise with a screwdriver to open it and bleed the cooling system.
Open the coolant reservoir tank by turning the cap on the top of the tank counterclockwise. Pour engine coolant into the reservoir when the coolant starts to escape the bleed screw. Continue pouring the coolant into the tank until there are no more air bubbles coming out from around the bleed screw.
Close the bleed screw, turning it clockwise with the screwdriver. Shut off the engine.
Loosen the bleeder screw, which is on top of the thermostat housing assembly, by turning it counterclockwise with the screwdriver. The coolant will flow out of the housing without the engine on.
Tighten the bleeder screw by turning it clockwise when you no longer see air bubbles coming out of the screw.
Set the heat temperature on the HVAC controls inside the car to the hottest setting, and set the fan to the highest speed.
Start the engine and let the car run.
Open the cap on the coolant reservoir tank by turning the cap counterclockwise and pulling it off the tank. Watch the coolant level, indicated by the marks on the side of the tank, and pour in more coolant if the level drops below the lower mark.
Open the bleeder screw again once the E34 has reached normal operating temperature. Then tighten the screw after there are no more air bubbles coming out around the screw. Check the coolant level in the reservoir tank periodically, and refill it to the upper mark on the tank as needed.
Repeat Step 6 until all of the air is out of the radiator and cooling system. You may need to repeat the process five or six times to fully bleed the system. Turn off the car.