1984 300D Variable speed electric fan conversion

[kestreltom]

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

[BWhitmore]

With the clearance shown between the water pump pulley fasteners and the new fan, I would be concerned about engine shifting during acceleration, etc. you may want to consider a different type fastener for the water pump pulley that does not have such a tall head. Looks great and hope it does what you want.

[kestreltom]

Originally Posted by BWhitmore

With the clearance shown between the water pump pulley fasteners and the new fan, I would be concerned about engine shifting during acceleration, etc. you may want to consider a different type fastener for the water pump pulley that does not have such a tall head. Looks great and hope it does what you want.

That's a good idea. You can't see it in the pic, but there is actually a good 5/8" or so of clearance. I plan to make a custom aluminum water pump pulley with a smaller diameter at some point, so will use lower profile countersunk screws in that prototype.

[BillGrissom]

Ford used a 2 spd fan (Taurus, etc) that many rodders use, and I recall Ford and Volvo have ties, so could be the same or similar.

Several people on the old Mopar sites I visit have tried replacing their mechanical fan with an electric and realized poorer cooling. It is hard to beat a mechanical fan/clutch that is working. There are more efficiency losses in running electric. It will be interesting to see your results.

In our M-B, the electric fan is just for the AC condenser, and does that job fine when the fan runs, but the control system seems reluctant to turn it on. RollGuy re-designed so it always turns on when the AC clutch is engaged, though it then runs even when not needed (highway). Perhaps a redesign so it turns on w/ AC clutch plus a temp switch set lower than the standard PN would perfect it.

[funola]

kestraltom,

IIRC, didn't you already build your own PWM motor controller for a Volvo electric fan? What's different about this one other than with a new radiator?

How would one test the Volvo electronic fan in the fields? The wreckers would just connect a battery up to it which from from I found online, would do nothing. Can damage occur to the electronics if the wires are connected incorrectly, e.g. reverse polarity?

[tjts1]

From the pic it looks like you're already running a larger than stock alternator?

[kestreltom]

Originally Posted by funola

kestraltom,

IIRC, didn't you already build your own PWM motor controller for a Volvo electric fan? What's different about this one other than with a new radiator?

How would one test the Volvo electronic fan in the fields? The wreckers would just connect a battery up to it which from from I found online, would do nothing. Can damage occur to the electronics if the wires are connected incorrectly, e.g. reverse polarity?

Sorry Funola, I have been remiss in not checking the replies over time...

I did build a custom analog controller for this purpose, but later went with an Arduino controller in order to make it simpler and easier for others to reproduce. I will post the sketch if there is interest.
These Volvo fans are cheap enough ($27) at the local U-Pull that I did not have them checked by hooking them up. They seem to be very robust, but I bought a spare anyway.

Update: I have had no issues at all with the fan & controller. The arduino has a lcd screen that I use to monitor the return coolant temp from the radiator to the engine block, which tends to remain very low compared to the dash temp. The dash temperature seems to be rock steady under all but the most grueling hot days climbing mountains at 75 mph at 6000' msl. Even then it only blips up on the gauge to about 100C, but even then it is more likely that the exhaust backpressure from the gt2256v working to make boost is the cause. I am not 100% sure if the electric fan & thick core radiator are the cause, but my fuel efficiency is also improved. Even when the electric fan runs at full speed and pulls 21 amps, that is still only about 300 watts... or .4 hp - that's less than 1/2 horsepower! I have made many trips up to northern New Mexico getting better than 40 mpg. I know there are doubters out there, so I have been very careful to fill the tank on the level, and use gps data to derive the miles.

Interesting factoid: Although I used a vacuum device to fill the radiator & cooling system a few years ago, it still took about 15 months for the last air bubble to work its way out. When it did, there was a significant improvement in steadiness of the dash temp gauge, the engine ran cooler under all conditions, and I had to add about 12 oz of coolant fluid. I am never opening the coolant system again... I can be patient - just not for air bubbles!

[kestreltom]

Originally Posted by tjts1

From the pic it looks like you're already running a larger than stock alternator?

TJTS1 - Yes, I am running a 140 amp unit from a Saab. I also moved and ugraded the battery to a 160 amp/hr gel cell in the trunk. Heavy, but starts the car with authority and gives a better weight distribution to make better use of the double rear sway bars and propigskin springs.

[kestreltom]

Here is a link to the analog circuit design. See the text file for in-depth information about the circuit and how it works.

https://drive.google.com/open?id=1R77h5-eu4F3kMvUz35QZ6YqFufSEQmnK

Go for it!