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DIY KTM Radiator Fans


GasitandCrash

After experiencing some overheating while going slow in rough terrain I decided to try a cheap fix and install a couple of cooling fans. Here are some photos of my fan installation.

 

The fans are not sealed but since they are brush-less DC fans, unless some debris gets in them they should not be affected by the environment. The fans are fairly inexpensive draw very little current and easy to replace if they fail. The fans are held on the radiator by zip ties. I inserted one zip tie through each of the radiator side mounting holes of the fan then passed the zip ties through the fins if the radiator and secured them with the clipped-off head of another zip tie.

 

The 2006 250 xc-w does not appear to have a 12vdc circuit. It does have an output from the generator that I assume is alternating current. Since the stock regulator only has one wire going to it and ground on the other side I suspect is just a zener diode, that acts as a voltage limiter shunting anything over a certain voltage to ground. If that is the case the AC generator output would be fine for lights and a horn, but not a Direct Current Fan. I installed a inexpensive (cheap) aftermarket regulator/rectifier, inserting it between the generator and the rest of the KTM's electrical circuit. You can see the voltage regulator in the attached photos. The regulator/rectifier provides 12vdc to the fans, horn, lights and the battery.

 

The battery pack is a ni-mh 1800 mha 12vdc, NOT lithium-ion. I opted for the ni-mh because there is less of a fire hazard in-case the voltage regulator goes nuts. The battery is connected to the rest of the circuit with a 7.5 amp fuse and is intended to act as a voltage conditioner. If the voltage provided by the regulator has any rpm related spikes, or dips, the battery should absorb the spikes by charging, and fill any dips by discharging. Or at least that's the plan. The battery also powers the fans if the radiators are still hot when the engine is not running.

 

The fans are activated by an appliance thermo-snap switch. This switch is a normally open bi-metal switch that closes at 85c (185f). It is designed to switch 120vac at 8 amps. That is an order of magnitude more current then the fans require, so they are not likely to fail due to current draw. If it fails it will probably be a result of exceeding the cycle life of the switch and I have NO idea of how many cycles to failure this switch is rated for. It is attached to the radiator just below the radiator cap near the hot coolant in hose using JB weld epoxy adhesive. The switch activates after the stock thermostat opens fully and the coolant temp at the top of the radiator exceeds 85c.

 

Since installing the fans, a coolant recovery bottle and a 1.8 bar radiator cap, even though I have been riding harder, I have not experienced any steam from overheating. I have seen the coolant recovery bottle over half full. So the cooling system with the fans running has gotten hot enough to overpressure the 1.8 bar radiator cap and over flow coolant into the recovery bottle, but it did not over flow the bottle, and all of the coolant was returned to the radiator as soon as the bike cooled. The fact that the coolant bottle did have coolant overflow in it is proof that the fans and 1.8 bar radiator cap are not a total cure to overheating. Though as I said overheating has happened far fewer times even though I'm riding more and harder than last year. The thermo-snap switch ensures that the whole system is automatic requiring no input from the rider. The fans turn on and off according to radiator temperature whether the engine is running or not. The fan system weighs less than 1 kg (2 lbs). All in all I am very satisfied with the way it works.

 

I know the wiring is a rats nest. It was pretty much a proof of concept job. My son was going to clean it up and give it a more professional look, but I haven't gotten it over to him yet (1year+)

 

>>> See my coolant recovery bottle system HERE.

 

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Sofasco, a company in winchester va makes all sorts of sealed harsh enviroment fans for cheap. See what the have laying around and pick your size and ctm. Great idea!

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