Coolant: Make sure that the coolant is mixed properly. BMW part number 82 14 1 467 704 is my choice. Pure antifreeze does not cool (transfer heat) as well as water. So this is one situation where more is not better. Although pure water boils at a lower temperature than antifreeze, water actually dissipates heat better. So don't exceed a 50% mix when filling the system. Its best to research the volume of coolant the system in your vehicle holds and mix a true 50/50 mix in a bucket. Then pour the mixture into the cooling system. We recently reduced cooling system temperature in Supercharged BMW e46 M3 by almost 20 degrees by reducing the coolant to water ratio to 40% antifreeze and 60% water. Remember to switch back for cool winter weather.
Faulty radiator cap: The radiator cap BMW item # 17114379047 is the pressure relief valve of the cooling system. At approximately 17.4 P.S.I. the cap is designed to release the stored pressure. This is to avoid damage to some of the cooling system components. However the systems needs to have the 17.4 P.S.I. of pressure to increase the coolant or water boiling point. Without a cap the coolant will boil out of the system as you drive down the road. So, check the radiator cap carefully. Make sure the seals and "O" rings are in good condition. If in doubt replace it, they are cheap. DO NOT install a generic cap purchased at a local parts store. The fit and the pressure rating are critical. I have repaired many cooling system issues by simply replacing the radiator cap.
61311364273, and the white is the low speed (91degree) BMW part number 61311364272. Each switch has 2 electrical connectors. To test the fans operation, turn on the ignition (don’t start the engine) and simply use a small screw driver and touch the 2 terminal on the white switch together. The low speed of the electric aux. fan should now be running. Do the same with the red switch terminals and see if the high fan speed comes on. Note when switching on A/C the low fan speed should come on at all times. If the fan does not come on either speed check the fuses. If the fan does not come on in the low speed test the fan resistor BMW part number 17 40 1 373 177 located on the outer fan housing in front of the radiator behind the front grill.
Low temperature auxiliary fan switch: There is a simple trick you can do to make the auxiliary fan come on much sooner to help keep temperatures under control. To do this you will need to remove the red switch (99 degree) and discard it. Then move the wires from the red switch over to the terminal of the white 91 degree switch. Purchase a new 82 degree switch from BMP design and install it in the now vacant hole of the 99 degree switch. To install the remaining wires you will need to change the slip on spade connectors to the larger sizes. What you have now created is an auxiliary fan system that engages the low speed at 82 degree, rather than 91 degrees, and the high speed at 91 degrees, rather than at 99 degrees. To purchase the lower temperature auxiliary fan switch order item number 61 31 6 364 271.
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The categories below are for a 1987 BMW 325e E30.
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