Manual override for fan clutch

[MikeBeggy]

I wanted to share my new found fan control circuit thanx to fellow member Matt400. I was searching forums on transmission cooling and Matt posted his ideas on how he wired the viscous fan to come on at drivers discretion. I have an 05 and I used a 1k ohm potentiometer to fool the computer into turning the fan on. It turns out that my fan doesn't engage until 218 degrees. I like that I can manually engage the fan now to come on during slow reverse driving, long hard pulling up hills or when the trans temps are higher than I like. The only side effect that I can find is the compter raise the idle speed when in park to about 1000. May not be a bad thing here in Arizona when I leave the truck idling for a few minutes. BTW, Matt used a 180 ohm resistor for his 03 and mine turned out to be 500 ohm to simulate 225 degree coolant temps.

 

[JStieger]

Mike-



Do you have any pics or elec diagrams of the install by any chance?



Thanks-

 

[MikeBeggy]

If you look under transmission temperature in this forum you can see Matt400's diagram. The switch is a single pole double throw toggle available at any electronics place. I used a 1k potentiometer to simulate the factory coolant sensor. Mine seemed to work best when the computer sees 225 degrees. I soldered in 530 ohms resistors today since they seem more stable than potetiometer.

 

[posey-smoker]

Fan clutch early engagement

My fan clutch engages too fast. What I mean by that is this morning I drove to work. It was 70 degrees out. I turned off the truck at 7:30am. At 11:45 am I left for lunch. When I got in the truck and started it up the engine temp was cold and all the way to the left. Outside temperature at 11:45 is now at 79 degrees. As soon as I put it in drive and took off the fan was engaged.



This almost happens every time. Sometimes it doesn't come on but mostly it does.



Sometimes it doesn't even come on when the engine is fully hot and its a hot day out.



Any thoughts

 

[CLAYTON]

Here ya go

Here it is... ... .

Here is a copy of my MFO (Manual Fan Override) circuit I developed. The fan is PWM (Pulse Width Modulated) by the ECM and fan speed is also monitored which is why I did it this way for no engine codes.



This works on my 03 and I later found out that on an 04 you must use a different resister because DC decided to change the CTS (Coolant Temp Sensor) that reports a different voltage range to the ECM. I don’t recall the resistor to use on the 04 but remember it needed to have more resistance than the one for the 03’s possibly 700 or more ohms.



It’s pretty simple and basically what you need is a toggle that will change over the CTS signal to the resister circuit that is pulled to ground. The resister needs to be low enough in resistance to tell the ECM the coolant is 220 degrees and that is a 180 ohm resister for the 03’s. If you use one that allows the gauge to go too high you will set a fault code.



Don’t be alarmed when you see lower oil pressures with the MFO on because you have “told” the ECM the coolant temp is hot so it reports a lower oil pressure reading thinking the oil is thinner.



Another feature that surfaced is if you leave the MFO on for 8 minutes the ECM will automatically elevate the idle RPM's to 1000 so the fan will draw even more air over the coolers. In this mode the PWM circuit then begins to cycle the fan on-off-on etc. . This function only works in park and will disable as soon as you shift out of park.

 

[Bill Stockard]

My fan clutch engages too fast. What I mean by that is this morning I drove to work. It was 70 degrees out. I turned off the truck at 7:30am. At 11:45 am I left for lunch. When I got in the truck and started it up the engine temp was cold and all the way to the left. Outside temperature at 11:45 is now at 79 degrees. As soon as I put it in drive and took off the fan was engaged.



This almost happens every time. Sometimes it doesn't come on but mostly it does.



Sometimes it doesn't even come on when the engine is fully hot and its a hot day out.



Any thoughts

The fan clutch will engage based on engine coolant temperature and high pressure in the A/C system. If the refrigerant pressure gets too high when there's not enough ram air coming through the condenser, the fan clutch will engage even if the engine is cold.



Bill

 

[navyramman]

How about an elec fan and take off the HP robbing fan off of the eng. What CFPM will be needed to keep that beast cool?

 

[MikeBeggy]

The viscous drive fan clutch on our trucks engages with a variable slope depending on outside temp, ground speed, engine temp, AC head pressure and only enough to get the job done. On my 05, it doesn't fully engage until 218 degrees engine coolant temp. Any electric fan that could do the same job would be much larger and use more energy since the conversion of mechanical energy to electric is much less than 100%. I think the new fan clutch is a step in the right direction for more efficient cooling.

 

[navyramman]

But you will not rob the eng of HP when you need it going up a hill or pulling from a stop light after the eng has been sitting on a hot day in traffic. Yes you will be Turing the alternator to feed that Elec beast, but that will feed the batters up over time. Yes on paper and over time you will get worst fuel mpg using the Elec fan. But for people that want that fan to run when just sitting in traffic or at the stop light or going up the big hill and want that fan to run could just push a button or switch and it goes from auto to on or off. People that drive Dodges want control, that is one of the reasons I see an AC on/off button in the cab and not in the Fords. When I had a Chevy I put one in it. I want control of my AC Compressor. Power baby.

Greg

 

[DMcGalliard]

Clayton,
I know it has been a while since you posted the manual fan clutch override but I am getting ready to do mine. I am unclear as to where to make the connection. Can it be done where the wires come out of the fan housing at the bottom of the radiator or at the cts or ecm?. I will appreciate your help.

Dave Mc

 

[redfuelrules]

I'd also like to know this.



Ben