View Full Version : manual radiator fan switch

10-26-2003, 04:36 AM
A couple of summers ago, the temp sensor switch failed. This isn't uncommon on K bikes. The symptom was steam rising alongside the fuel tank in the vicinity of the radiator filler cap. And the temp guage pegging in the red. I thought the radiator had sprung a leak, and kept going by refilling the overflow tank with water at every stop, and by shutting off the engine at stop lights.
A mechanic at a BMW shop helped me trace the problem. The radiator, fan, and hoses were all OK. We installed a switch that triggered the fan relay. Home again, I cleaned up the switch installation on the left handlebar, but also replaced the temp sensor, which is buried down under the fan, behind the radiator, and generally requires tearing the bike apart.
Now, when pulling into town after a long hot run, I don't wait for the sensor to trigger the fan relay, I just switch on the fan before the temp rises above normal. The switch also lets me know the fan relay and fan motor are working.
Considering the difficulty of replacing the temp sensor on the road, I highly recommend that K bike owners install a manual fan switch. It's relatively easy to dig into the electrical box, locate the fan relay, and tap a wire into the harness. The wire goes to the switch and from the switch to ground. Might save your vacation some day.