Now that summer is just around the bend, I think it is as good a time as any to share what I did to improve the cooling on my 300D.

Summer in Albuquerque, especially when you are stuck in traffic (which fortunately doesn't happen often) can sometimes tax even a healthy cooling system in the venerable W123. My A/C blows ice cubes, and I like to use it without having to watch the temperature gauge like a hawk - so one day I noticed one of these at the local U-Pull and decided to take it home and see if I could make it work.



This particular fan came out of this:



So I took it home and did some probing. This fan is a relatively powerful unit... there are heavy red & black dc power leads as well as a smaller green pwm input wire. When connected to 12vdc power, it didn't do anything until the correct pwm is supplied on the signal wire at the right fixed frequency. By supplying a variable pulse width that is linked to the radiator coolant temperature sensor it is possible to have a closed loop control system that maintains the coolant output from the radiator within a user defined temperature range by adjusting airflow through the radiator. The fan speed is inversely proportional to pulse width, and thus it reaches full speed at a pulse width of about 6% and turns off at a pulse width of 94%. At full speed it pulls about 21 amps and runs at about 2k rpm. The fan turns off at pulse widths outside the range this range of 6% – 94%, which means that the pulse stream must be constrained to the range of valid values – which make a digital controller like the Arduino a perfect candidate for the job.

I was already the proud owner of a 19" h x 21.5" w aluminum cross-flow radiator with a 2-1/2" core that I bought with the silly dream of getting it shoehorned into my car. Think it will fit? Think I can also squeeze that Volvo fan in there too?



Crazy, huh?

Well... what I discovered was that if your turn the Volvo fan sideways and trim the fan shroud to fit the radiator height-wise, it almost snapped right into place!



I fashioned a block off plate out of aluminum & silicone rubber to cover the gap at the top between the old fan shroud and the new radiator, cut off the plastic bottom from my old radiator and mounted on the bottom of the new radiator so it would drop into place, and fashioned some clips from some uni-strut cut-offs I had laying around, to hold everything in place.



I mounted it in the car sans the original fan & clutch to check the clearances, and it fit! (just barely)



Next up: Part 2 - the electronics