The performance of a vehicle can often be enhanced by making strategic modifications that target parasitic losses and improve system efficiency. One such modification that has gained popularity among car enthusiasts is the conversion from a mechanical engine fan to an electric fan setup. In this article, we will explore how converting to Derale dual electric fans can lead to a significant horsepower increase, specifically a 12 hp gain in a Mustang GT, and explain the engineering principles that make this possible.

Understanding Electric Fan Conversion

Electric fans provide several advantages over traditional mechanical fans. A mechanical fan is bolted directly to the water pump pulley and spins constantly whenever the engine is running, regardless of cooling demand. This creates a continuous parasitic drag on the engine that can rob 8 to 15 horsepower at high RPM. An electric fan, by contrast, operates only when needed, activated by a thermostatic switch or engine control unit (ECU) signal. When the engine is cool or the vehicle is moving at speed, the fan can remain off, completely eliminating that parasitic load.

The Physics of Parasitic Loss

Understanding why mechanical fans consume so much power requires a look at basic physics. The fan must overcome air resistance to spin, and the power required increases with the cube of the fan speed. At highway RPM, the mechanical fan may be spinning at 4,000 RPM or more, requiring significant engine output just to keep it moving. An electric fan, powered by the alternator, draws electrical load that is generally much lower than the mechanical equivalent. The alternator itself creates some drag, but the net gain still favors the electric setup.

Quantifying the Savings

In controlled dyno tests, converting a Mustang GT from a mechanical fan to a high-quality electric fan setup has been shown to free up between 10 and 15 rear-wheel horsepower. A 12 hp gain is well within realistic expectations when using a properly sized dual fan system like the Derale units. This gain is most noticeable during acceleration and at higher RPM, where the mechanical fan's drag is highest. For a daily driver, this translates to improved throttle response and a more immediate power delivery.

Benefits of Electric Fans Beyond Horsepower

While the horsepower gain is the headline, the benefits of electric fans extend into several other areas of vehicle performance and reliability. These advantages make the conversion a comprehensive upgrade rather than a single-purpose modification.

Improved Fuel Efficiency

Because the engine no longer has to waste energy spinning a fan constantly, fuel efficiency can improve by 1 to 2 miles per gallon in mixed driving conditions. The electric fan only engages when coolant temperatures rise above a set threshold, typically around 200°F. On the highway, where airflow from vehicle speed is sufficient, the fan may not run at all, further reducing fuel consumption.

Enhanced Cooling at Low Speed

Electric fans excel at low-speed and idle conditions. When crawling in traffic or off-road, the mechanical fan may not spin fast enough to provide adequate airflow. Electric fans can be controlled independently to run at full speed regardless of engine RPM, ensuring consistent cooling performance. This is particularly important for high-performance applications like the Mustang GT, where heat management is critical.

Quieter Operation and Increased Reliability

Mechanical fans create a constant roar that can be fatiguing on long drives. Electric fans operate quietly until they are needed, reducing cabin noise. Additionally, removing the heavy mechanical fan and clutch assembly reduces front-end weight, which improves steering feel and suspension response. Electric fans also have fewer moving parts that wear out over time, and they do not place side-load stress on the water pump bearings, potentially extending water pump life.

Key Benefits Summary

  • Reduced engine load and parasitic loss
  • Improved fuel efficiency by 1–2 mpg
  • Enhanced cooling performance at low speed and idle
  • Quieter operation and reduced cabin noise
  • Increased reliability with fewer wear items
  • Weight reduction on the front of the engine

Choosing Derale Dual Fans

Derale is a well-known brand in the automotive cooling industry, offering high-quality electric fans designed for performance applications. Their dual fan setup provides ample airflow to keep your engine cool, especially during demanding driving conditions such as track days, towing, or hot-weather cruising. Derale fans are engineered with high-output motors and balanced blades to deliver consistent airflow with minimal vibration.

Derale Product Line Overview

Derale offers several series of electric fans, but the dual fan kits are specifically designed for vehicles that require high airflow capacity. The dual configuration allows two fans to work in parallel, covering a larger surface area of the radiator core. This design improves heat rejection and allows for redundancy—if one fan fails, the other can still provide partial cooling.

Derale fans are available in puller and pusher configurations. For most Mustang GT applications, a puller fan mounted behind the radiator is the preferred choice, as it pulls air through the radiator core more efficiently than a pusher fan mounted in front.

Specifications of Derale Dual Fans

  • CFM (Cubic Feet per Minute): Combined airflow up to 3,000 CFM
  • Voltage: 12V DC, compatible with standard automotive electrical systems
  • Fan diameter: 14 inches each, for a total coverage area of approximately 28 inches
  • Mounting: Universal fit with adjustable mounting brackets for various radiator sizes
  • Motor type: Sealed, high-torque DC motor with ball bearings
  • Shroud: Included rigid shroud ensures directed airflow across the entire radiator surface
  • Warranty: Typically one-year limited warranty from manufacturer defects

Why Derale for a Mustang GT?

The Mustang GT's engine bay is relatively spacious, making it well-suited for aftermarket cooling upgrades. Derale's dual fan kits include all necessary wiring, relays, and temperature sensors, simplifying installation. The fans are designed to handle the thermal load of a modified engine, making them an excellent choice for owners who have added superchargers, nitrous, or high-compression heads. Derale's official website provides detailed fitment guides and technical specifications.

Real-World Performance Gains: The 12 HP Claim

The claim of a 12 hp increase from installing Derale dual fans is not marketing hyperbole—it is based on repeatable dyno results from multiple independent testers. To understand how this gain is achieved, we must examine the dyno testing process and the conditions that maximize the benefit.

Dyno Testing Methodology

In a typical before-and-after dyno test, the vehicle is strapped to a chassis dynamometer and run through a series of pulls. The first pull is performed with the stock mechanical fan and clutch assembly in place. Then, the mechanical fan is removed, and the Derale dual electric fans are installed. The vehicle is allowed to cool to the same starting temperature, and another series of pulls is conducted. The difference in horsepower and torque curves is recorded. Environmental factors such as ambient temperature, humidity, and barometric pressure are monitored to ensure consistency.

Typical Results

In these tests, the horsepower gain at the rear wheels is consistently in the range of 10 to 14 hp, with 12 hp being the most common figure. The torque curve also sees improvement, often gaining 10 to 15 lb-ft of torque in the mid-range where daily driving occurs. These gains are achieved without changing any other engine components, making the fan conversion one of the most cost-effective horsepower upgrades available.

Factors Influencing Performance

  • Quality of installation – Proper wiring and fan placement ensure maximum airflow
  • Condition of other engine components – A well-maintained engine will show greater gains
  • Type of driving conditions – Stop-and-go traffic amplifies the cooling benefit
  • Calibration of the engine management system – Aftermarket tuning can optimize fan control
  • Ambient temperature – Hotter climates may see less dyno gain but more real-world benefit
  • Radiator condition – A clean, efficient radiator provides better heat rejection

For a deeper dive into the science of electric fan horsepower gains, Mustang6G forums contain extensive discussions and user-submitted dyno sheets.

Installation Process

Installing Derale dual fans in a Mustang GT can be a straightforward process if you follow the right steps. The entire job can typically be completed in one afternoon by a DIY mechanic with basic tools. Below is a detailed guide to help you through the installation.

Tools Required

  • Socket set with metric and SAE sockets
  • Wrenches (combination and ratcheting)
  • Screwdrivers (flathead and Phillips)
  • Wire cutters and strippers
  • Electrical tape and heat shrink tubing
  • Mounting hardware (included with Derale kit)
  • Multimeter for electrical testing
  • Drill with assorted bits (if modifying brackets)
  • Safety glasses and gloves

Step-by-Step Installation

  1. Disconnect the battery – Remove the negative battery terminal to prevent accidental electrical shorts or fan activation during installation.
  2. Remove the existing mechanical fan and shroud – Unbolt the fan clutch from the water pump pulley using a fan clutch wrench if necessary. Remove the fan shroud by unbolting it from the radiator core support.
  3. Prepare the Derale dual fan assembly – Inspect the fan shroud for any shipping damage. Attach the mounting brackets to the shroud according to the included instructions. Derale kits typically use adjustable brackets that can be positioned to match your radiator's thickness.
  4. Install the fan shroud onto the radiator – Position the shroud with fans over the radiator core. Secure the shroud using the provided hardware. Ensure the fan blades do not contact the radiator fins—there should be at least a 1-inch clearance. Adjust mounting brackets as needed.
  5. Route the wiring harness – Derale kits include a relay and fuse assembly. Mount the relay near the battery in a dry location. Route the positive wire from the battery to the relay. Connect the fan wires to the relay output. Use zip ties to secure wiring away from moving parts and exhaust heat.
  6. Install the temperature sender – Most Derale kits include an adjustable thermostatic probe. Insert the probe into the radiator fins near the top tank, or splice into the radiator hose. Alternatively, you can wire the fans to an in-cab switch for manual control.
  7. Connect the electrical system – Attach the ground wire to a clean chassis ground point. Connect the relay trigger wire to an ignition-switched power source so the fans can only operate when the key is on. Verify all connections with a multimeter.
  8. Reconnect the battery and test – Reconnect the negative battery terminal. Start the engine and allow it to warm up. Observe the fan operation—they should turn on when the coolant temperature reaches the set point (typically around 200°F). Check for any unusual noises or vibrations.
  9. Final inspection – Double-check all bolts for tightness. Verify that fan wiring does not interfere with the serpentine belt or pulleys. Ensure the radiator cap is properly seated and coolant level is correct.

Installation Tips for Best Results

  • Use a relay and fuse at the battery to protect the electrical system
  • Consider upgrading the alternator if adding other high-draw accessories
  • Test fan function with the engine off by temporarily jumping the thermostatic switch
  • Seal any gaps between the shroud and radiator with foam tape to prevent air bypass
  • If the fan kit includes a variable speed controller, use it to reduce noise at low load

For additional guidance, Install University offers comprehensive wiring diagrams and troubleshooting guides.

Cooling System Considerations

Converting to electric fans requires a holistic view of the engine's cooling system. Simply adding fans without addressing other components may not yield the full benefit. The radiator, water pump, and thermostat all play roles in heat management.

Radiator Compatibility

The Mustang GT's stock radiator is generally adequate for street use, but owners who track their cars or live in hot climates may benefit from an upgraded aluminum radiator. Derale dual fans pair well with aluminum radiators that have a larger core volume and more efficient fin design. When selecting a radiator, confirm that the mounting surface is flat and that the fan shroud can be securely attached.

Water Pump and Thermostat

With the mechanical fan removed, the water pump no longer has the fan load, which can reduce wear on the pump bearings. However, the water pump still needs to circulate coolant effectively. A high-flow water pump and a low-temperature thermostat (160°F or 180°F) can further improve cooling system performance. This combination is commonly used in performance applications to maintain consistent engine temperatures.

Electrical System Load

Electric fans draw significant current—typically 10 to 15 amps per fan at full speed. The Derale dual fan setup may draw a combined 20 to 30 amps. This load is within the capacity of a standard Mustang GT alternator (typically 130 amps or higher), but owners with multiple aftermarket electrical accessories should verify available headroom. Upgrading to a 200-amp alternator may be necessary if adding sound systems, lighting, or other high-draw items. Performance World offers high-output alternators specifically for late-model Mustangs.

Tuning and ECU Integration

For maximum performance, integrating the electric fan control into the ECU can provide precise temperature management. Many aftermarket tuners and handheld programmers allow the user to set fan on/off temperatures. This feature is especially useful if you have installed a lower-temperature thermostat.

Fan Control Strategies

There are three main approaches to controlling electric fans:

  1. Thermostatic probe – A standalone sensor mounted in the radiator that triggers the fan relay at a preset temperature. This is simple and reliable, but does not communicate with the ECU.
  2. ECU control – The engine computer controls the fan relay based on coolant temperature sensor input. This allows for precise temperature targets and integration with other engine management functions.
  3. Manual switch – A toggle switch in the cabin gives the driver full control. Useful for track use where cooling demand varies rapidly.

For most street Mustang GT owners, ECU control is the preferred option. It ensures the fans operate exactly when needed, with no user intervention.

Potential Tuning Adjustments

After installing the fans, you may notice the engine runs cooler, especially in traffic. Some tuners recommend adjusting the fan on temperature to around 195°F and the off temperature to around 185°F. This keeps the engine in its optimal operating range without cycling the fans excessively. An overly aggressive fan setting can cause the fans to run constantly, reducing their lifespan without any performance benefit.

Cost-Benefit Analysis

Converting to electric fans is one of the most affordable horsepower upgrades for a Mustang GT. The Derale dual fan kit typically costs between $250 and $400, depending on the specific model and included accessories. Installation time is generally 2 to 4 hours. Compared to other mods that offer similar gains—such as a cold air intake or exhaust system—the electric fan conversion provides excellent value per dollar.

Comparison with Other Mods

Estimated Horsepower Gain per Dollar
Modification Estimated Gain Approximate Cost Cost per HP
Derale dual electric fans 12 hp $300 $25/hp
Cold air intake 10–15 hp $350 $23–35/hp
Cat-back exhaust 10–20 hp $700 $35–70/hp

While both cold air intakes and exhaust systems are popular upgrades, the electric fan conversion offers a unique benefit: it reduces parasitic loss, which improves efficiency across the entire RPM range without affecting emissions or sound. For owners who plan to add more power later, the fan conversion also improves cooling capacity for future modifications. Superchargers Online notes that many forced induction kits include electric fan upgrades as part of their recommended supporting modifications.

Troubleshooting Common Issues

Even with a quality kit and careful installation, occasional issues may arise. Here are the most common problems and their solutions.

Fan Does Not Turn On

If the fans fail to activate when the engine is at operating temperature, check the following:

  • Verify that the relay is receiving power from the battery
  • Check the ground connection for cleanliness and tightness
  • Test the thermostatic probe by jumping the two wires—if the fans spin, the probe is faulty
  • Confirm that the fuse is not blown
  • Use a multimeter to check voltage at the fan connectors

Fan Runs Continuously

If the fans never shut off, even when the engine is cold, the likely cause is a stuck relay or a short circuit in the trigger wire. Disconnect the thermostatic probe and see if the fans stop. If they do, replace the probe. If they continue running, the relay may be welded shut and should be replaced.

Noisy Operation

Excessive fan noise can come from imbalances in the fan blades, contact with the shroud, or resonance with the radiator. Inspect the fan assembly for debris or damage. Ensure all mounting bolts are tight. If the noise persists, consider adding rubber isolation washers between the shroud and radiator.

Insufficient Cooling

If the engine still runs hot after installation, check for air pockets in the cooling system, a stuck thermostat, or a low coolant level. Verify that the fans are pulling air through the radiator (not pushing air away). Also confirm that the fan shroud covers the entire radiator face to prevent air bypass.

Conclusion

Converting to electric fans, particularly the Derale dual fans, can provide significant benefits for Mustang GT owners. The combination of improved cooling efficiency and reduced engine load leads to a genuine horsepower increase—realistically 12 hp at the rear wheels—along with better fuel economy, quieter operation, and enhanced reliability at low speeds. This modification is straightforward for a DIY mechanic and represents one of the best value-for-money upgrades available for the S197 and S550 Mustang GT platforms.

Whether you are building a daily driver, a weekend track car, or a show-quality cruiser, the Derale dual fan conversion is a proven step toward a more efficient and powerful vehicle. The 12 hp gain is not just a number; it is a tangible improvement that you will feel in the seat of your pants every time you press the throttle.