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Discussion Starter · #1 ·
I just completed the installation of a radiator cooling fan onto my 2003 WR450F. In case there is another rider interested in doing this to their bike, I thought I would share the process. We ride a lot of relatively slow technical and rocky stuff, at 10,000 ft or higher, so overheating is sometimes an issue. The fan should also help keep the bike cool when plowing through snow or deep mud, where the radiators will not see much air flow.

The fan is a high quality, Italian made pull fan manufactured by SPAL. The particular fan I used is a 4" fan, which I mounted behind the left side radiator. The fan runs on 12V, and draws 2.0 amp once it's running, and about 7 amp during a brief start-up. I connected the fan directly to the battery, and switched it with a toggle switch (audi) that I mounted between the odometer and the power switch, behind the number plate. I purchased a trickle-charger type connector, so that I can connect the bike's battery to the fan circuit, when the trickle charger is not connected. I replaced the trickle charge fuse with a slightly higher value fuse (10 amp). I decided to use a switch to activate the fan, rather than deal with the complexities of a thermostat circuit and relay. Below are photos of the installation.

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Going to try to make it automatic

Thanks for the info. I bought the same fan but instead of a manual switch to turn it on I have ordered an inline temperature switch in a radiator hose T connection that I found on ebay. They said I could wire the switch directly to the fan but I decided against doing that. I have installed a street legal kit and I wanted the fan to only come on when the key is on. You could do the same thing with the factory power switch also.

So instead of direct wiring the inline temp switch to the fan I am going to install a relay and wire the fan directly to the battery through the relay on the power side. Then on the control side of the relay I will have the temperature switch and ignition key switch in series so that both have to be on to activate the fan.

I don't want to do this without a relay because I don't want to pull up to 7 amps through the key switch...or really even the temperature switch for that matter.

Since I installed the street legal kit there was already a leftover +/- circuit that was originally used for the headlight (I think) that I used for hooking up a micro USB device to power my GPS unit that is switched from the ignition key. I am planning on piggybacking on that to provide power to the temperature switch since the switch and the control side of the relay won't draw hardly any current.
 

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radiator fan using switch and relay

I've almost finished putting this together.I have everything done except the fan mount. I elected to use a Derale 16743 generic fan mount kit instead of a bracket because it was much easier and the fan basically sits on the lower edge of the radiator so the rods aren't really carrying any weight and just keeping the fan in the right place.

I tested it and it really works great. It was about 100 degrees here today and I let the bike idle in the sun for a few minutes. Once it warmed up the fan would kick on and off. It ran about 45 seconds every 2 1/2 minutes which made me feel good that the fan was able to easily pull the temperature down quickly even in 100 degree weather in direct sun. I wouldn't even worry about being stuck at a light in Phoenix at 2 PM on a hot summer day because the fan would probably be on maybe half the time.

I ended up getting the relay at Radio Shack. I ordered a "mini-relay" from Amazon and it was huge...HUGE...so I sent it back. You can't see the relay it because it is up behind the frame but it is small enough to satisfy me. I got most everything else from ebay...the switch, the fan, even the vinyl tubing I ran all the wiring in, the fuse holder and even some of the connectors I used. It was just so easy.
 

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