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KTM 450 EXC RFS Overheating Solution - Server Fans? Yup!
2005 KTM 450EXC with aftermarket oversized gas tanks kept overheating while operating in slow technical conditions in the south Texas and northern Mexico summer heat. This setup should work on just about any bike as long as it has an M14X1.5 bung in the radiator.

I had already installed an overflow tank. It helped but I wanted to take it a step further.

There are no commercial fan solutions available that I'm aware of that will work with the big Acerbis, Safari, IMS, or Clarke gas tanks. I have a stock tank, IMS 3.9 Gallon, and an Acerbis 6.6 Gallon. It works with all of them.

I've been running this setup for well over a year and have done several demanding trips including Big Bend National Park and various places in northern Mexico. Most of the time, temps have been in the high 80s to low 100s. Speeds were often little more than crawl/walk speed. It also included at least a couple hundred miles of 45-70 mph runs down nasty washboarded dirt roads and a couple hundred pavement miles with occasional speeds of 90+. Lots of vibration, lots of hard suspension hits. The fans have been abused well beyond their intended purpose, but they continue to work perfectly!

I've rode through a couple mild rain showers and stream crossings where water sprayed pretty heavy into the fans. Full disclosure here...they were not running at the time. I've never completely submerged them in water, but I have sprayed them with a garden hose while running.

The second fan has never came on automatically while riding or even while idling. The first fan seems to do a great job of keeping things cool enough for it not to be needed. I like having it as a backup though. Just in case.

I'll run down the overall concept and give a parts list at the end.

With the switch in “Standby”, Fan #1 turns on at 195F, fan #2 turns on at 210F. I can't remember the specs, but I think they turn off at about 10 degrees below their turn on temps.
They can both be turned on manually with the switch if desired.

I used a three way, (on-off-on) waterproof, illuminated rocker switch. I used a 10 pin Molex connector behind the headlight fairing to make it easy to remove and re-install the fairing.

The ON position with an Amber indicator light is the “Standby” position.
The ON position with a Red indicator light is the manual “Override” position. The red light also illuminates when a fan turns on automatically.
Off would be my, yep, you guessed it... the “Off” position.
I fashioned a little box out of styrene plastic for the switch and mounted it on the backside of the headlight fairing.

I attached two 120mm x 25mm 175CFM water and dust resistant server fans to the radiators using zip-ties.

These are BMW part numbers that you can order through Amazon or anywhere that has BMW parts. I'm using the higher temp switch, but you can go with the other if you want the fans to turn on sooner.

#61131378412 – plug housing
#61130007445 - wire, small, x2
#61130007446 - wire, large
#61318361787--BMW temp switch turns on at 180° and 195°
#61311378073--BMW temp switch turns on at 195° and 210°

I purchased the fans, switch, and connector through Amazon.

Fans (2): Adda 120mm x 25mm Case Fan 12V DC 175CFM Waterproof to IP55 Ball Bearing 2 wire
Switch: GAMA 232e3-b/b
Connector: Molex, 10 Circuit Connector -1 Complete Set- Wire Conn. with Pins - Molex Mini-Fit Jr (This connector requires that you crimp the wires. They're small pins, and if you don't have the proper crimping tool, you may have some problems. I happen to have a set similar to these, not perfect but they worked: IWISS Weather pack Crimper Tools for Crimping Delphi Packard Weather pack Terminals or Metri-Pack Connectors)

Many of these RFS motors are getting long in the tooth now, so I don't know if anyone out there wants or needs this information. If you do, and want more details, just let me know.

Premium Member
1,943 Posts
Job well done

Brilliant and simple soloution! Well engineered and executed. Well done and thank you for sharing. I have copied your post for future reference. Best regards
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