Upgrading the cooling fan system on an RB-series engine is one of the most effective modifications for maintaining consistent operating temperatures, especially for street-tuned or track-driven Nissan Skylines and other RB-powered vehicles. The stock fan setup often falls short under increased boost, higher ambient temperatures, or prolonged idling in traffic. This comprehensive guide provides step-by-step instructions for installing an upgraded cooling fan system, from selecting the right components to final testing. Whether you are a weekend DIY enthusiast or a professional mechanic, these guidelines will help you achieve a reliable, high-performance cooling solution for your RB engine.

Understanding the Need for an Upgraded Cooling Fan

RB engines, particularly the RB25DET and RB26DETT variants, generate significant heat due to their compact design and high power output. The factory viscous fan can struggle to move enough air through the radiator when the engine is modified or when the vehicle is used in demanding conditions such as track days or stop-and-go traffic. Common symptoms of inadequate cooling include rising coolant temperatures, reduced power, and heat soak that affects intake air temperatures.

An upgraded cooling fan system delivers several key benefits:

  • Increased airflow – High-performance electric fans or improved mechanical fans push more air through the core, enhancing heat rejection.
  • Elimination of fan clutch drag – Electric fans remove parasitic loss from the engine, freeing up horsepower.
  • Better temperature control – Thermostatically controlled electric fans activate only when needed, reducing noise and improving warm-up times.
  • Space savings – Slim electric fans can fit into tight engine bays where a bulky mechanical fan may not.

For these reasons, many RB enthusiasts choose to replace the stock fan with an upgraded unit, often moving to a dual electric fan setup or a high-flow mechanical fan with a custom shroud.

Tools and Materials Needed

Before beginning the installation, gather all necessary tools and parts. The exact components will depend on whether you choose an electric fan conversion or a high-performance mechanical fan upgrade.

Essential Tools

  • Socket set with metric sizes (10mm, 12mm, 14mm, 17mm common)
  • Ratchet and extensions
  • Wrench set (combination wrenches)
  • Flat-head and Phillips screwdrivers
  • Pliers and wire cutters/strippers (for electric fan wiring)
  • Multimeter for testing electrical connections
  • Cooling system flush kit or a large drain pan
  • Funnel and coolant mixing container
  • Protective gloves and safety glasses

Materials and Parts

  • Upgraded cooling fan kit (e.g., SPAL, Davies Craig, Mishimoto, or a custom dual fan setup)
  • Fan shroud (if not included with the kit)
  • Coolant (ethylene glycol or waterless type, as per vehicle specs)
  • Distilled water (if mixing coolant)
  • Electrical relay and fuse holder (for electric fan installations)
  • Temperature switch or adjustable thermostat controller
  • Wire, connectors, heat shrink tubing
  • Zip ties and electrical tape

Popular options for RB engines include the SPAL 16-inch high-output fan, the Davies Craig EWP and fans, and purpose-built kits from companies like Mishimoto that are designed for specific chassis such as the R32, R33, or R34 Skyline.

Safety Precautions

Working on a cooling system involves hot coolant, sharp parts, and electrical wiring. Follow these safety measures:

  • Allow the engine to cool completely before opening the cooling system. Hot coolant can cause severe burns.
  • Always disconnect the negative battery terminal before starting any work to avoid short circuits or accidental fan activation.
  • Wear protective gloves and safety glasses when handling coolant and tools.
  • Work in a well-ventilated area, especially when draining coolant.
  • Use jack stands and wheel chocks if the vehicle needs to be raised.

Preparation Steps

Proper preparation ensures a smooth installation and prevents complications.

1. Drain the Coolant

Place a drain pan under the radiator. Open the radiator drain valve (typically located at the bottom of the radiator) or remove the lower radiator hose. For RB engines with a block drain, you can open that as well for a more complete drain. Dispose of old coolant in accordance with local regulations.

2. Remove Obstructions

Clear the area around the front of the engine. Remove the air intake ducting or any hoses that might interfere with access to the fan assembly. If your vehicle has an aftermarket intercooler piping, you may need to temporarily loosen it to gain clearance.

3. Disconnect the Battery

Use a wrench to disconnect the negative terminal and move the cable away from the battery post. This prevents accidental startup or electrical shorts during the removal process.

Removing the Stock Fan System

The procedure varies slightly depending on whether your RB engine came with a viscous fan clutch or a standard mechanical fan. Most RB engines use a viscous clutch mounted directly to the water pump pulley.

Stock Viscous Fan Removal

Using a large wrench (or a special fan clutch tool), hold the water pump pulley in place while loosening the nut securing the fan clutch. On many RB engines, the nut is left-hand threaded – confirm before applying force. Once loose, remove the fan and clutch assembly together. Then unbolt the fan shroud (usually 10mm bolts) and lift it out of the engine bay.

Inspect the water pump pulley and belt condition while they are exposed. If the water pump shows signs of leakage or wear, this is an ideal time to replace it.

Removing Electric Fan Systems (if applicable)

If the vehicle already has an aftermarket electric fan, disconnect the wiring harness and remove the fan assembly from the radiator. Remove any mounting brackets or zip ties.

Set aside all reusable mounting hardware.

Installing the Upgraded Fan System

Now the new components go in. Follow the manufacturer’s instructions for your specific kit, but the general steps are outlined below.

Mechanical Fan Upgrade

If you are staying with a mechanical fan, install the new clutch and fan blade onto the water pump pulley. Ensure the fan is positioned so the blades sit fully inside the shroud. Install the shroud over the fan and bolt it to the radiator core support. Check clearance carefully – the fan blades must not make contact with the shroud or any hoses.

Electric Fan Conversion

For an electric fan system, the process is more involved but offers greater control.

  1. Mount the Fan(s) – Position the electric fan against the radiator (puller configuration is typical). Use the included mounting hardware or zip ties to secure the fan to the radiator core. Ensure the rubber pads or brackets prevent metal-on-metal contact.
  2. Install the Shroud – If your fan kit includes a shroud, attach it around the fan to direct airflow evenly.
  3. Route Wiring – Lay the power and ground wires along existing harnesses, avoiding hot surfaces and moving parts. Install the relay and fuse near the battery.
  4. Connect the Thermometer Switch – Install the temperature sender in the radiator end tank or use a hose adapter. Connect the signal wire to the relay trigger.

Many enthusiasts prefer a dual fan setup for high-power RB builds. A quality kit like the SPAL dual fan system can move over 2,000 CFM while fitting within a standard RB radiator core.

Electrical Wiring Considerations

Proper wiring is critical for electric fan reliability. Undersized wire or poor connections are common failure points.

  • Use a 30-40 amp relay for each fan.
  • Run 10-12 gauge wire from the battery positive to the relay, and from the relay to the fan.
  • Ground the fan directly to the chassis with a short, heavy gauge wire.
  • Trigger the relay with a 12V source that is only active when the ignition is on (to prevent the fan running with the engine off).
  • Include a manual override switch inside the cabin for track use.

A detailed wiring guide can be found in many automotive forums, such as the SAU (Skylines Australia) electrical section.

After wiring, test the fan by applying power directly to confirm rotation direction – the fan should pull air through the radiator toward the engine.

Coolant Refill and Bleeding

With the fan installed and wiring safe, it’s time to refill the cooling system.

  1. Close the radiator drain valve and reconnect any hoses removed.
  2. Mix coolant and distilled water (typically 50/50) in a separate container.
  3. Pour the coolant slowly into the radiator until full.
  4. Start the engine with the radiator cap off. Turn the heater to maximum (if equipped) to open the heater core valve.
  5. Squeeze the upper radiator hose to help dislodge air pockets.
  6. As the engine warms, watch for coolant level dropping; add more as needed.
  7. Once the thermostat opens, you will see coolant flow and bubbles. Continue until no air is visible.
  8. Top off, install the radiator cap, and check for leaks.

For RB engines, it’s common to have an air bleeder screw on the thermostat housing or on the intake manifold water pipe. Loosen this screw while filling and retighten once coolant streams out.

Testing the System

Reconnect the battery and start the engine. Allow it to idle and monitor the electric fan operation (if applicable). The fan should engage when the coolant temperature rises to the set point (usually around 80-90°C or 180-195°F, depending on your thermostat spec).

Take the car for a gentle drive, then a more spirited run. Watch the temperature gauge carefully. With an upgraded fan, the gauge should stay steady even during prolonged idling or low-speed driving.

Check for any unusual noise from the fan, vibration, or coolant leaks around hoses and the radiator. Address any issues before considering the installation complete.

Final Checks and Long-Term Maintenance

Once you’re satisfied with the operation, perform these final steps:

  • Retighten all bolts and screws, especially the fan mounting hardware and shroud fasteners.
  • Secure all wiring with zip ties away from heat and moving parts.
  • Double-check the coolant level after a few heat cycles – topping up may be needed.
  • Periodically clean the radiator fins and the fan blades to maintain efficiency.
  • Inspect the fan wiring connections and relay for corrosion every six months.

For additional tips on maintaining your RB engine’s cooling system, refer to the Nissan Sport Magazine cooling guide.

Troubleshooting Common Issues

Even with a careful installation, problems can arise. Here are a few common issues and solutions:

Fan Does Not Turn On

  • Check the fuse and relay.
  • Test the temperature switch with a multimeter (should close when hot).
  • Verify the ground connection is solid.

Fan Runs Continuously

  • The temperature switch may be shorted or wired incorrectly.
  • If using a manual override switch, ensure it is in the AUTO position.
  • Check the relay for a stuck closed contact.

Overheating Still Occurs

  • Confirm the fan is pulling air (not pushing).
  • Check for air pockets in the cooling system – re-bleed thoroughly.
  • Inspect the radiator for blockages or insufficient core size.
  • Ensure the water pump is functioning properly.

Fan Noise or Vibration

  • Check fan blade balance – re-center if necessary.
  • Ensure the fan is not contacting any hoses, wires, or the shroud.
  • Tighten all mounting bolts.

Conclusion

Installing an upgraded cooling fan system on your RB engine is a rewarding modification that enhances reliability and performance, especially in modified or high-stress conditions. By following this detailed guide, you can ensure the installation is done safely and effectively. Whether you choose a high-flow mechanical fan or a fully controlled electric conversion, the investment in better thermal management will protect your engine and keep it running at its best.

Remember to always use quality components and take your time with wiring and bleeding. A well-installed cooling fan system is a long-term upgrade that pays dividends in every drive.