The Big Chill: A Budget Approach to a Big Electric Fan that Really Works

Installing a big electric fan and relays isn’t difficult and doesn’t have to be expensive. This new MK8 fan from RockAuto and three-relay kit from Hollister Road offers excellent two-speed electric fan control that should be more than enough to cool most street cars. Best of all, this whole package will run roughly $220.

Installing a big electric fan and relays isn’t difficult and doesn’t have to be expensive. This new MK8 fan from RockAuto and three-relay kit from Hollister Road offers excellent two-speed electric fan control that should be more than enough to cool most street cars. Best of all, this whole package will run roughly $220.

Words and Photos by Jeff Smith

We all know it’s never been easier to make serious horsepower. But, with all that power is the need to control all the heat that comes along for the ride. Only a third of the heat generated in the combustion chamber ends up pushing the pistons down to make torque. A second third goes right out the tailpipe. It’s the final third portion of this equation we are concerned with here, because all that heat ends up pumped to the radiator. It’s that heat in the middle of a sweltering, 115-degree August afternoon in Arizona we need to contend with here.

The industry is full of temperature control solutions such as aluminum radiators, fans, shrouds, switches, and the like. A pile of these parts can get expensive in a hurry, so we’re always on the hunt for money-saving ideas that will get us where we need to be without having to take on another part-time job to fund it. One of the factory electric fans that has enjoyed immense popularly is the Lincoln MKVIII fan.

Enthusiasts who sing this 18-inch air mover’s praises pronounce near-mythical performance figures that are not always accurate. Most of the material about this fan for this story comes from Dave Chapman, owner of Hollister Road, a company that sells a very nice relay system for this fan that we will get to momentarily. Chapman lives in Texas, where managing cooling systems is an essential skill for hot rodders.

To begin with, there are several variations of this fan. While its origins can be traced to the ’93-’98 Lincoln MVIII (we’ll use MK8 from here on), Chapman says the original MK8 was a single speed fan that was managed by a factory variable-speed controller. Since this is a single-speed fan, it’s not interchangeable with the 18-inch diameter, two-speed ’94-’97 Thunderbird and Cougar models. There’s also a smaller, 17-inch Taurus two-speed fan that is also a bit thinner that might work for smaller radiators. This can be found under Dorman PN 620101. We’ve listed all the part numbers and connectors in the Parts List at the end of this story.

There are also claims on the internet of typhoon-like 4,000 cfm ratings for the MK8, but Chapman says the reality is closer to 3,000 cfm (on high speed), which is still impressive. This ability to move a large volume of air also creates an equally impressive electrical current load. We’ve created a chart, from information Chapman supplied, that lists the electrical power demands, but at high speed, the load is close to 35 amps.

The reason the two-speed model is attractive is multi-fold. All electric motors create a very high current spike when first energized. This instantaneous load spike immediately settles into continuous running amperage that is significantly lower. Triggering the fan first from the slow speed side reduces the instantaneous current draw, making it easier on the charging system.

You could go junkyard hunting for these fans, since these late ‘90s cars are still around. But, why bother when you can buy a brand new Dorman 2-speeed electric fan from RockAuto for $67 plus shipping? It even comes with a warranty. This is the fan we will be working with in this story.

One challenge for some early performance cars might be simply squeezing this 5.5-inch deep fan within that often confined space between the radiator and the water pump. If you own a ’70 Monte Carlo, that’s not going to be an issue, but for the rest of the world, that 5.5-inch fan depth could be a problem. Plus, not all radiators will accommodate this fan’s 24-inch shroud width.

For the small-block Chevy crossflow aluminum radiator in our early El Camino, the fan fits fairly well, but we will need to perform some minor fabricating, including trimming some of the plastic shroud, to allow room for the radiator hoses.

The Hollister relay package feeds power to the relays from a very nice 50-amp fuse holder. Carrying a spare 50-amp fuse would also be a good idea.

The Hollister relay package feeds power to the relays from a very nice 50-amp fuse holder. Carrying a spare 50-amp fuse would also be a good idea.

With a fan this powerful, attention will also be needed on the electrical side. When a fan pulls as much as 45 amps, you need an electrical switching system that is more sophisticated than a clunky mechanical switch with sausage-like 10-gauge wires running under the dash. Hollister Road has created a lineup of relays and temperature switches specifically designed to control these one- and two-speed Ford cooling fans.

Let’s spend a moment on relays and how they work. A relay is a great way to trigger a high-amperage-demand device like this MK8 fan while using a very low-amp switch. Relays are rated on their amperage capacity. Chapman chooses high-quality 60-amp Bueler relays to control both the low and high-speed sides of this fan and offers several different part numbers based on your needs. For our system, we chose a three-relay kit that comes with a pair of temperature sensor switches. The first 60-amp relay controls the fan’s slow speed triggered with the 185-degree F sensor. When engine temperature exceeds 200 degrees F, the second and third relays combine to feed power to the high side of the fan. Hollister also offers a relay kit for air conditioned cars that employs a fourth relay that triggers the fan’s high-speed side (regardless of engine temperature) whenever the A/C is switched on.

These relay kits may appear to be a bit pricey, but the reason is the higher quality parts that are employed, including a 50-amp inline fuse holder. The relays use silver-coated contacts that prevent arcing, which improves their durability, while incorporating an internal resistor that prevents what is called electrical “flyback.” All electric motors instantly become generators, as they continue to spin after power is switched off. This current can travel back into the charging system as electro-magnetic interference (EMI), causing potential damage to digital components like an EFI computer or transmission controller. Plus, Chapman uses high-quality SXL wire that is more heat resistant than the typical wire you buy at the auto parts store.

Hollister Road also offers a robust, 85-amp rated pulse-width modulation (PWM) controller. PWM offers a “soft start” feature where the fan begins slowly and gradually increases its speed to match coolant temperature. This minimizes the initial amp surge of big fans. This controller can be mounted either in the engine compartment or the interior.

Hollister Road also offers a robust, 85-amp rated pulse-width modulation (PWM) controller. PWM offers a “soft start” feature where the fan begins slowly and gradually increases its speed to match coolant temperature. This minimizes the initial amp surge of big fans. This controller can be mounted either in the engine compartment or the interior.

If you are looking for a bit more sophisticated fan control, Hollister sells a pulse-width modulation (PWM) controller. We’ve already mentioned how a simple relay can create a rather large load spike when the fan first kicks on. PWM controls the fan with a series of voltage pulses that can be measured as a duty cycle. So, instead of hitting the fan with 100 percent (full voltage), the PWM controller applies full voltage for only 20 percent (for example) over a given time period. This creates what is called a soft start so the fan begins to spin very slowly at first.

Mounting the MK8 fan to this Holley Frostbite radiator will require cutting some access holes in the built-in shroud. Always mount an electric fan to permanent external mounts. Never mount an electric fan to the radiator core using those cheap zip ties. Fan vibration will eventually cut through the tubes on a horizontal radiator or damage the fins on a vertical radiator.

Mounting the MK8 fan to this Holley Frostbite radiator will require cutting some access holes in the built-in shroud. Always mount an electric fan to permanent external mounts. Never mount an electric fan to the radiator core using those cheap zip ties. Fan vibration will eventually cut through the tubes on a horizontal radiator or damage the fins on a vertical radiator.

As an example of PWM control, let’s assume a time period of one minute. If the controller applies power to the fan with a PWM duty cycle of 50 percent, the controller will cycle on and off, applying power to the fan over a period of short voltage bursts of one second on and one second off so the fan receives power for only 30 seconds out of the 60-second total. As a result, the fan will run at essentially half speed. Most soft starts begin at a lower duty cycle (like 20 percent) and then slowly increase fan speed with the coolant temperature. Essentially what this does is make the fan speed proportional to the coolant temperature. This is far more sophisticated than simply turning the fan on full speed from a dead stop, incurring a huge load spike.

Mounting the MK8 fan to this Holley Frostbite radiator will require cutting some access holes in the built-in shroud. Always mount an electric fan to permanent external mounts. Never mount an electric fan to the radiator core using those cheap zip ties. Fan vibration will eventually cut through the tubes on a horizontal radiator or damage the fins on a vertical radiator.

Mounting the MK8 fan to this Holley Frostbite radiator will require cutting some access holes in the built-in shroud. Always mount an electric fan to permanent external mounts. Never mount an electric fan to the radiator core using those cheap zip ties. Fan vibration will eventually cut through the tubes on a horizontal radiator or damage the fins on a vertical radiator.

So, as you can see, there are lots of options when it comes to controlling engine temperature with a large, high-volume electric cooling fan. But best of all, you don’t have to spend a large portion of your car-building budget to achieve excellent results. The combination of our MK8 two-speed fan, relay package, and connector comes to just under $220, which is less than the cost of many fan packages that may not move as much air. It’s more about knowing what is available and where to look for the quality parts.

Current Draw

All loads are expressed in amps. The load spike is rated with the fan started on the low side. Starting the fan on the high side would create a much higher spike. This test was performed using Hollister’s relay kit.

Fan Continuous Load Spike
T-Bird/M8 Low Spd. 26-28 37-40
T-Bird/M8 High Spd. 32-35 48-53
Taurus Low Speed 24-26 36
Taurus High Speed 28-29 40-45

Make the Connection

Wire Connection
10-Ga. Red (from fuse box) Battery 12v+
16-Ga. Purple 180 F sensor
16-Ga. Green 200 F sensor
14 Ga. Yellow Switched 12v+
10 Ga. Red (from relay) Fan low speed
10 Ga. Blue Fan high speed
10 Ga. Black Fan ground

Parts List

Description PN Source Price
Dorman, Thunderbird, 18” 2-speed fan 620118 RockAuto $66.99
Dorman, Taurus, 17” 2-speed fan 620101 RockAuto $85.79
Standard Motor Fan connector S725 RockAuto $21.79
MK8 relay, no switches TM8BA0000 Hollister Road $69.95
MK8 relay, 185 and 200 F switches TM8BA1820 Hollister Road $129.95
MK8 relay w/AC no switches TM8AC0000 Hollister Road $109.95
MK8 relay w/AC 185 and 200 F switches TM8AC1820 Hollister Road $149.95
PWM fan controller, 85 amps PWMRT85 Hollister Road $249.95
Powermaster 140 amp alternator CS130 478021 SummitRacing $165.97
Holley Frostbite aluminum radiator FB-124 SummitRacing $269.96
Purple Ice corrosion protection,1 pt. 01600 SummitRacing $9.99
No-Rosion corrosion protection, 1 pt. N.A. Norosion.com $10.95
HyperKuhl corrosion protection, 1 pt. N.A. Norosion.com $13.95

Sources: Applied Chemical Specialties, norosion.com; Holley Performance Products, holley.com; Hollister Road Co., hollisterroad.com; Powermaster, powermastermotorsports.com; RockAuto, rockauto.com

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About the author

Jeff Smith

Jeff Smith, a 35-year veteran of automotive journalism, comes to Power Automedia after serving as the senior technical editor at Car Craft magazine. An Iowa native, Smith served a variety of roles at Car Craft before moving to the senior editor role at Hot Rod and Chevy High Performance, and ultimately returning to Car Craft. An accomplished engine builder and technical expert, he will focus on the tech-heavy content that is the foundation of EngineLabs.
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