E39 BMW 540i Custom Auxiliary Fan DIY (Cooling Overhaul Part 5 of 5)
The E39 5-series is an amazing car, but some thing BMW went a little overboard with the technology. The cooling system is way too complicated with the electric thermostat and the 2 bar pressure cap. Switching to a lower temp thermostat, electric fan, and a new radiator has really help my confidence in the car. The next step is to add an aux fan.
The factory fan has been broken since I bought the car, and they are way over priced. The aux fan is programmed to be on whenever the AC is on (my AC is always on). So, I decided to wire up a small 12 inch fan to run whenever the engine is running. it is the same as the factory fan would be as I always have the AC turned on. I wish it would turn off over 40 mph, but i will install a switch to disable it for long highway trips. So far, it is working great and preventing the main fan from coming on as often.
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