When your motorcycle starts running hotter than usual—especially in traffic or after idling for a few minutes—the culprit is often a failing radiator fan. This small but critical component plays a big role in regulating your engine’s temperature, preventing overheating, and maintaining performance and longevity. If the fan isn't kicking on when it should, you're looking at potential engine damage or, at the very least, a frustrating roadside breakdown.
Common Radiator Fan Failures
Before diving into diagnostics, it’s important to understand what commonly goes wrong in a motorcycle’s radiator fan system. Most modern bikes use an electric fan mounted behind the radiator that’s triggered by a temperature sensor and powered through a relay circuit. Here are the usual suspects when something fails:
-
Blown Fuse: The simplest issue, often overlooked.
-
Bad Fan Motor: Over time, the fan motor can burn out due to high use or exposure to water and debris.
-
Faulty Thermoswitch: If the temperature sensor fails, the fan never receives the signal to start.
-
Worn or Corroded Relays: These mechanical switches can fail or get stuck, breaking the power flow.
-
Broken Wiring or Connectors: Damaged or corroded wires can prevent voltage from reaching the fan.
Symptoms that your radiator fan might not be working include overheating while idling, the fan not audibly spinning when the engine gets hot, or erratic temperature fluctuations on your dash.
Diagnostic Testing Procedures
Once you've identified that your radiator fan isn’t functioning properly, it’s time to troubleshoot each component. You’ll need a multimeter, some basic tools, and a bit of patience.
Checking Electrical Connections and Fuses
Start with the basics:
-
Locate the fan fuse—this is often found in the fuse box under the seat or near the battery. Remove it and inspect for a break or dark burn marks. If blown, replace with the same amp rating and see if the fan works.
-
Inspect connectors—look for corroded or loose plugs going to the fan motor, thermoswitch, and relay.
-
Wiggle test—with the bike running, gently wiggle the wiring harnesses near the fan and sensor. If the fan kicks on intermittently, you’ve found a weak or broken connection.
Don’t underestimate the power of clean, tight electrical connections. About 30–40% of fan issues stem from corroded terminals alone.
Bench-Testing the Fan Motor
If the fan still doesn’t activate with the engine running hot, it’s time to bench-test it directly.
-
Remove the fan plug from the harness.
-
Using jumper wires, connect the fan terminals directly to a 12V battery—observe polarity. If the fan spins, the motor is still good.
-
If the fan doesn’t spin, it’s likely dead and needs replacement.
Remember to always wear gloves and safety glasses during this step—the fan can spin up quickly and with force.
Testing the Thermoswitch
Most bikes use a temperature-activated switch threaded into the radiator or thermostat housing. This sensor completes the ground circuit to activate the fan relay.
Here’s how to test it:
-
Identify the thermoswitch (usually one or two wires coming from the radiator).
-
With the engine off and cold, use a multimeter set to continuity mode across the terminals—there should be no continuity.
-
Heat the area gently with a heat gun or warm up the engine. Once the coolant hits 190–220°F, you should hear a click or see continuity establish across the switch.
-
No change? The thermoswitch may be faulty.
For more advanced troubleshooting, check your service manual for the exact temperature threshold and resistance specs.
Relay and Power Circuit Tests
The radiator fan relay is usually located near the fuse box. Its job is to allow high-current power to flow to the fan when triggered by the thermoswitch.
To test:
-
Remove the relay and inspect for signs of rust or melting.
-
Use a multimeter to test continuity between terminal pins (usually labeled 85, 86 for coil; 30 and 87 for load).
-
With 12V applied to the coil pins, you should hear a click and get continuity between the load pins.
If it fails to click or show continuity, replace it. A weak or stuck relay can prevent fan activation, especially after extended use.
Repair vs. Replacement: Which to Choose
Once you’ve identified the failing part, you’re faced with a decision: should you repair the issue or replace the component altogether?
Repair Considerations
Repairs can be cost-effective and satisfying—especially if the fix is something simple like a new fuse, relay, or wire connection. For budget-conscious riders or those with rare bikes, repair is sometimes the only option.
However, repeated overheating caused by deferred repairs can lead to head gasket failure, warped cylinder heads, or worse. If the component is suspect, it’s often smarter to replace it rather than risk major engine work.
When Replacement Makes Sense
For high-mileage motorcycles or bikes exposed to off-road elements, components like the fan motor or thermoswitch may simply wear out. Replacement is generally recommended when:
-
The fan motor fails a bench test.
-
The thermoswitch doesn't activate at proper temps.
-
The relay sticks intermittently.
-
Wires are corroded beyond a clean repair.
Swapping out these components is relatively easy and can be completed with hand tools and a basic understanding of your bike’s wiring diagram.
Comparing OEM and Aftermarket Fans
If you're replacing your radiator fan, you’ll find both OEM (Original Equipment Manufacturer) and aftermarket options on the market. Which route should you go?
OEM Fans
Pros:
-
Guaranteed fitment
-
Backed by factory specs
-
Reliable performance
Cons:
-
Expensive (often $150–$300)
-
Limited availability for older models
-
May not handle high-performance applications well
Aftermarket Fans
Pros:
-
Cost-effective (typically $60–$150)
-
Available in high-performance models (greater airflow, sealed bearings)
-
Can be lighter or more compact
Cons:
-
May require custom mounting
-
Varying quality—stick with trusted brands
-
Potential wiring differences
When choosing an aftermarket fan, look for units with waterproof connectors, sealed motor housings, and corrosion-resistant blades. Many are designed to move more air than OEM units, which is great for riders who see a lot of stop-and-go traffic or hit the trails in hot climates.
Get Back on the Road with Confidence
Diagnosing radiator fan issues on your motorcycle doesn’t have to be a mystery. By methodically testing your fuses, wiring, fan motor, relays, and switches, you’ll know exactly what’s working—and what’s not.
Remember: A functioning radiator fan is essential for engine longevity and riding comfort. Whether you're replacing a worn-out thermoswitch or upgrading your cooling system with a high-output fan, every rider should be proactive about their bike’s temperature control.
Looking for Reliable Parts? Trust Myler’s Inc.
When it’s time to replace your fan motor, thermoswitch, or even the entire radiator, don’t gamble with cheap or untested parts. Myler’s Inc. has been supplying high-performance, track-tested, and trail-tough cooling components for over two decades.
We stock:
-
Radiators and fans for all major motorcycle brands
-
Cooling system parts for dirt bikes, street bikes, ATVs, UTVs, and snowmobiles
-
Aftermarket and OEM-compatible options
-
Accessories, hose kits, and more
Whether you're maintaining your daily commuter or prepping a race bike, Myler’s is your one-stop source for cooling system excellence.
Shop now or call our expert team for recommendations tailored to your ride. Your engine—and your next adventure—deserve nothing less.