Electric Fan Installation

In the never-ending quest to squeeze every last bit of horsepower from our Trophy Stock (now Street Warrior) car, we installed a Black Magic 5.0 electric fan kit (Kit #175). This is a fifteen inch diameter electric fan that moves about 2800 cfm of air. I've borrowed the specifications from the Flex-a-lite catalog for informational purposes:

The fan has an adjustable thermostat that can be adjusted from 180-240 degrees depending on your cooling needs. For the street guys, the fan also has an air conditioning relay. The 5.0 specific kit comes with custom bracketry so that it bolts right up to your Fox body's existing radiator. For those of you running some of the thicker 3-row radiators, you may want to take some measurements to make sure the fan will clear your water pump pulley. The Black Magic fan is rated for applications up to something like 185 horsepower, but we've found it to be adequate for higher horsepower than that.

One of the great features of the fan is the adjustable thermostat. There is mechanical thermister that contacts the fins of the radiator and cycles the fan off-and-on depending on the setting. I marked several settings for my fan that corresponded to street and track conditions. While at the track, I set the thermostat higher to keep the fan from turning on during a 1/4 mile pass. This keeps the draw on the alternator lower which corresponds to less mechanical horsepower draw by the alternator from the engine. Then as I cross the finish line, I use a manual override switch to kick the fan "ON" and provide cooling while driving back to the pits. When I would drive on the street in warm weather, I'll turn the thermostat down a little so that the fan automatically cycles off-and-on at a temperature that corresponded with my cooling system thermostat. I also had the fan wired up so that it would continue to cycle "OFF" and "ON" after the ignition has been turned "OFF" (key "OFF") to reduce heat soak in the engine. This too is a feature built into the 'black box' of the Black Magic fan and is selectable by the user depending on the wiring configuration selected during installation. Some people don't care to have the fan cycle "OFF" and "ON" after shutting the car off. The Black Magic fan gives you this option as well.

I found the Black Magic installation instructions to be a bit lacking, especially in the wiring instructions. You should read the instructions thoroughly and even call the Flex-a-lite tech support hotline if you have any questions. But basically, the installation goes:

1. Drain radiator. Remove both hoses and disconnect the overflow tank's low indicator sensor.
2. Remove the serpentine belt.
3. Remove the stock fan & clutch assembly by removing the four bolts attaching them to the water pump shaft.
4. Replace the four attaching bolts (something's got to hold on the water pump pulley) and torque to specs. Put the serpentine belt back on at this point.
5. Remove the radiator by removing the two hold down clamps on the front support. The radiator will just lift out of the lower supports.
6. Remove the stock fan shroud and overflow tank. Save the clips as they'll be used later in the assembly process.
7. Assemble the bracketry and overflow tank according to the instructions.
8. Attach the Black Magic fan to the radiator according to the instructions. This is the point where the thermister is adjusted to touch the cooling fins of the radiator. I've found that you can GREATLY increase the reliability of the automatic control by applying heat sink compound between the thermister and the radiator to improve the heat transfer between the two. This compound can be found at any local Radio Shack or electronics store and is very similar to that compound used between the TFI module and distributor. Apply a liberal amount of the compound between the thermister and the radiator...better to have too much in there than not enough.
9. Reassemble the radiator and fan assembly back into the vehicle.
10. Wire the fan as shown in the following diagram.  If you plan on using the AC switch, you can add the additional circuitry as shown by the instructions provided with the fan.

The diagram shown above is how I wired my Black Magic fan. I ran the power leads off the hot side of the solenoid as shown so that the fan could be powered with the ignition in the "OFF" position.  Place the 30 amp circuit breaker as close to the source (solenoid) as possible to protect the circuitry from accidental meltdowns.

I'm going to pass along a very stern CAUTION at this point that Flex-a-lite doesn't give in their instructions.  Note that the third terminal of the toggle switch is not connected.  Normally this terminal would be taken to ground so that the switch illuminates when placed in the "ON" position [as instructed by the Flex-a-lite instructions].  Grounding this terminal out can be extremely dangerous if you use any other switch than that sold (at additional cost) by Flex-a-lite. It seems that grounding out any other manufacturer's switch can potentially cause an uncontrollable ground loop that will result in the entire amperage of the battery being drawn to ground through the switch.  I did just exactly as the Flex-a-lite instructions showed and nearly lost my car to the resulting melt-down that occurred as soon as I connected the battery!  Thank heavens I didn't immediately hit the road to try out the fan or else I would have lost the entire car!  When I called Flex-a-lite to tell them that their instructions were deficient, they informed me that they knew about the ground loop problem and had even been able to reproduce it in their shop!  Thanks for the warning Flex-a-lite!  That's why you'll see 5 amp in line fuses on both the supply and load lines at the switch. Actually, with the in line fuses there's no need to use 12 AWG wiring for the switch as its only powering a small relay.  With the fuse protection, 16 AWG wiring would be sufficient for the switch.

Update...

As our power output from the motor has grown over the years, the ability of the Black Magic fan to cool our engine during street driving became marginal.  At the last point where our car was seeing street duty, we were making about 425 horses at the crank and still using a stock radiator.  The engine temperature would become tough to maintain on those hot summer days and would actually come real close to overheating if we get stuck in traffic for very long.  Even after we upgraded to a 3-row aluminum Griffin radiator we were still having problems keeping the car cool during city driving. I think its probably best to stay close to Flex-a-lite's rating on the fan and limit its use to 350HP motors or less.  If you've got more power than that, I would recommend using a SN-95 style fan or even a dual fan arrangement. Believe it or not, we still have the Black Magic fan on our car to this day, more than five years after the original installation.  We're making about 600HP with the motor nowadays, but we're not asking the fan to work for long periods of city driving.  Even at our higher horsepower levels, the fan still does a good job cooling the car down on the way back to the pits after a run.