Radiator Fan Switch

[gbeaird]

When we got our '86, I discovered that the fan didn't come on at all. Luckily, we drove it home from Amarillo to Houston in the winter, and in the rain, most of the way (white-knuckle trip for me when my co-driver was behind the wheel, as she was enjoying the boost going down the highway on bald, wet, tires) =8-0. Anyway, once home, and checking it over, we discovered that the fan control module under the dash was literally melted. Since we were planning to pretty much just autocross the car, I opted to install a switch so we could control the fan, allowing us to cool it down between runs when the engine was off. This worked great 99.9% of the time, failing only once when we let a fellow competitor drive the car and he didn't know about the switch.

I still have that muscle memory. When I get in the car to start and run it, I turn the fan on immediately after starting it. I do like the switch, but I can see where others would want a temp-operated relay to do the work.

[svono50]

Thanks so much for the response. I've had this problem so many years, I was afraid the thread would be dead.
I know the fan motor itself works.
I have already changed the temperature sensor, although mine looks a little different, thicker brass part. I have also changed the dash relay, trying 2 other used parts.
I see in the manual that there is a 20Ga, fuse link near the master cylinder for the electric fan timer control unit feed, and shift light control unit, whatever that is.
Could that be the problem? I am mostly electric illiterate.

Let me do some digging in my manuals to see what I can find. The circuit is fairly simple from what I remember with only a couple of trigger points.

[Chuck]

When I removed the temperature sensor in the intake water jacket. I learned that the water passage was completely blocked with crud.

This may be the simplest solution...

[amassengale]

Thanks so much for the responses! I had not thought about crud in the water passage preventing switch heating. Now I'm thinking my first move should be to take a lighter to the switch and see if the fan comes on. I had flushed the cooling system, but maybe a better cleaning is needed.

[svono50]

Thanks so much for the responses! I had not thought about crud in the water passage preventing switch heating. Now I'm thinking my first move should be to take a lighter to the switch and see if the fan comes on. I had flushed the cooling system, but maybe a better cleaning is needed.

Lighter may work, but I would suggest getting a small pan on the stove with a liquid thermometer to see if the resistance curve of the switch works properly. The sensor should be a variable resistor that the EEC watches to see when to throw the signal to close the fan relay. I still need to dig into my archives as I just got my new PC at home up and running since I was greeted with a failed HDD on Christmas morning...luckily I had a slight warning a couple days prior to the failure and had backed up my files to a spare HDD.

[teal95]

Fighting fan not working and thought I'd add onto this thread rather than create another. Fan will turn by hand, but it's really stiff so probably effectively frozen. I suspect fuse or relay dead. I bought an electronic copy of the EVTM but of course it won't open, so can't use that. Found another fan I had squirreled away that seems reasonably loose, but no action there. Original issue was fan didn't come on when I was topping up the A/C. Unless I'm sitting in traffic fan never comes on except with A/C, which I'm guessing is part of the durability issue. Then tried just looking at DVOM but no voltage so it's farther up the circuit.

I have 83 and 84 GT turbos, 84, 85.5 and 86 SVO's and have had several 87/8 TC. I'm very familiar with the EEC operation of the cooling fans but this is the first time I've had to mess with the older cars fan system other than just replacing the fans. The 84 SVO is in the process of having the harness replaced with an RF harness and it will be getting an L* EEC. The 83 needs a harness also. While the 84 GT is an early build it doesn't have the wiring issue. I'm guessing that's because while it's an early build it has all the late parts, as I have documentation that it was a Ford test vehicle.