SN95 Mustang Fan and Variflow Fan Controller By Adam Dugger (Misc. Tech Section)
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We all know there are pros and cons using a belt driven fan to cool your pony. Although they work great for the cooling system, they do present a parasitic loss on the engine. Ford realized that in 1994 with the introduction of the SN95 Mustangs, offering an electric cooling fan as standard equipment. But this wasnt the first Mustang so equipped, as the 4 cylinder models had been using one, although their cooling requirements are much less.

There are electric fan kits on the market for the Mustang, but they (for the most part) do not offer enough cfm flow (cubic feet per minute) to adequately cool your modified or sometimes even stock pony. Then there is the added problem of not having a sufficient charging system to handle the extra draw an electric fan demands. Plus those of us with centrifigal supercharger face another hurdle in the way of clearance.

On my Vortech supercharged 88 GT, I sat down and devised a plan, using my own knowledge and the experience of others. I had been running a police spec fan clutch, along with a FMS 3 core brass radiator, Mr Gasket balanced 180 thermostat and edelbrock water pump. It kept the car nice and cool, but sometimes in severe traffic (welcome to NY) on hot and humid days the temp gauge would creep up to around 195-200.

I decided to use an electric cooling fan off a 1994-1995 Mustang GT as it flows plenty of air and is a relatively low profile fan to begin with.

The difference between the V8 and V6 fans is that the V8 has 3 terminals (high-low-ground) while the V6 has only 2. For what its worth, I am using the wiring harness plug from a V6, which you will read about later.

With the 8 rib blower setup and the 3core radiator, you are left with little breathing space. As you might be able to see in the picture above, the shroud of the fan has been clearanced from the 3o'clock to the 6 o'clock position. This will not affect cooling in any way, just offer clearance for the crank pulley.

Here is a pic with the OEM fan and shroud removed so that you have an idea of space:

I also elected to use the overflow from an SN95 Mustang to compliment the fan. Since I have my MSD box on one side and still have my battery under the hood, I am left with little room for an overflow catch can. Also, I prefer the stock look.

The fan is attached up top by drilling a hole on top on either side which the stock fan shroud screws will go through to the stock clips in the top of the radiator. You will have to reposition those clips to line up with the holes you have drilled. On the passenger side, I used the upper fan mounting screw to locate the overflow container with some metal stock with holes drilled in for various mounting points. I drilled a hole about 1/2 inch lower than the one already drilled to mount it a bit lower than the SNs do. There is very little room between the overflow and the upper radiator hose, but it can be done. Once mounted, I have about 1/8in clearance between the overflow and the 8rib tensioner pulley, just about the same as what I had with the stock shroud.

Down below, I used the same type of metal stock to hold the bottom of the overflow on. I drilled about a 3/8 hole in the plastic (its a mounting tab on the bottom) and secured it to the lower radiator support.

I acquired the OEM harness end from a 1994-95 V6 Mustang, but one from either V6 or V8 will work. Looks cleaner than simply putting quick crimps on it.

Now for the hard part. I already have the "3G" alternator found in the later Mustangs, so charging system capacity should not be an issue. I didn't want to simply hook up a switch and relay setup to the fan. I wanted something that would sense the temperature of the coolant/engine and adjust itself on and off accordingly. I had at one time been running a small 10in electric fan to supplement the stock fan, controlled by a Hayden thermostatic fan controller. Obviously that unit worked fine with a small draw fan, but would surely die if asked to handle the current draw of the SN fan. Modern electric fans can draw up to 70A to start the electric motor, then come down to a more reasonable draw once the fan is spinning.

According to PowerSystemManagement, the current draw can be explained as follows:

When a motor is rotating, an electromotive force (EMF) induces a voltage within the motor which is of the same polarity as the input voltage. This, in turn, works to reduce current consumption. When a voltage is applied to a non-rotating motor, no EMF is produced, resulting in higher current until the motor is up to normal speed. Unlike conventional controllers, which provide a fixed output voltage, the VariFlow unit provides a voltage to the fan which is dependent on engine temperature. As a consequence of the relatively slow movement in engine temperature, the voltage applied to the fan is ramped up at a slow rate. The slow ramp up in voltage avoids the high current condition of operation.

Moreover, the VariFlow unit employs a unique current control system which helps protect the control unit and the fan during "locked rotor" conditions. The smooth, variable output voltage also increases the life of the fan by limiting winding constriction and high torque conditions.
Obviously a Mustang which already has many electrical devices such as fuel pumps, high powered ignitions, stereo systems, etc. will benefit from NOT having a fan draw that much power on startup.
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