My temperature guage isn't working and my fan isn't kicking in

So, first i tested the wiring. I got a wire, pulled the connector off the sensor on the rad and attatched it to my wire. The other end of the wire to the neg on the battery. Fan kicks in.
So i got a tub of boiling hot water attatched the connector back to the sensor and dipped the sensor in the water..... nothing.

It was only by chance though that i noticed another sensor beneath the thermostat. So i'm now guessing that they're both temperature sensors and communicate :S somehow :S

I tested the guage itself, again with my wire. One end to the guage and one to earth. The guage shoots to hot.

So tested the wiring on the other sensor i've found. Put it to earth as i have done all the others and guage shoots to hot again.



I didn't remove the other sensor and dip it in how water though....


So which sensor is at fault? Or do i need to dip this other one in how water to determine?

bourney wrote:So i got a tub of boiling hot water attatched the connector back to the sensor and dipped the sensor in the water..... nothing.

The sensor on the rad is the fan switch, the reason it wouldnt have worked when dipped in the hot water is that it wasnt connected to ground/-ve.
The fan is permentantly hooked up to +12V, when the rad switch gets hot enough its series resistance falls and the other side of the fan motor gets hooked up to earth, 12V(ish) dropped across it and the fan spins. By taking it out, the temp switch wasnt hooked up to ground hence fan didnt spin.

If youve got a multimeter hook up one lead to top, and other to body of sensor. Then chuck it in hot water, it should show a large drop in resistance.

The one at the thermostat is for the the gauge. Not sure why that isnt working, as the gauge appears to be working, and the sensor its self appears to be working. Maybe some sort of loose con./wire, now that youve disconneced it and reconnected it may be fine?

I'm pretty sure the fan kicks in on most bikes at 104C+, so putting anything in boiling water (100C or less by the time you get it to the bike) isn't going to trigger it.

jac_is_smiling wrote:

bourney wrote:So i got a tub of boiling hot water attatched the connector back to the sensor and dipped the sensor in the water..... nothing.

The sensor on the rad is the fan switch, the reason it wouldnt have worked when dipped in the hot water is that it wasnt connected to ground/-ve.
The fan is permentantly hooked up to +12V, when the rad switch gets hot enough its series resistance falls and the other side of the fan motor gets hooked up to earth, 12V(ish) dropped across it and the fan spins. By taking it out, the temp switch wasnt hooked up to ground hence fan didnt spin.

If youve got a multimeter hook up one lead to top, and other to body of sensor. Then chuck it in hot water, it should show a large drop in resistance.

The one at the thermostat is for the the gauge. Not sure why that isnt working, as the gauge appears to be working, and the sensor its self appears to be working. Maybe some sort of loose con./wire, now that youve disconneced it and reconnected it may be fine?

Ok, that makes alot of sense. Thanks :D

I'm not so sure that the sensor under the thermostat is working TBH as i've only tested the wire going to the sensor (by putting it to earth) which made the guage shoot up.
I'm about to go out with a boiling pot of water and remove the sensor and dip it in the water and have a wire going from the body of the sensor to ground.
So hopefully this should show nothing on the guage and show the sensor is at fault?


I'll also check for a resistance drop on both sensors like you say.

Thank you for the help guys :D much appreciated :D:D