Diagnose Temperature Gauge Problems

By: Walt Briden
April 2003

All at once my temperature gauge on my '95 K1100RS would read one quarter scale for normal operating temperature instead of the usual one half scale.

Running in heavy traffic until the fan came on would not raise the needle above one quarter scale. Was the gauge stuck or was the sending unit defective?

Bob Carter explains that the sending unit resistance decreases as the temperature rises, which mine did, but it would not go below 95 ohms. This can be measured by pulling the black wire off the sending unit at the coolant drain location and measuring the resistance from the middle of the sending unit to the engine block.

What is the normal reading? Is 95 ohms normal? No! Brian Curry was nice enough to help me out here by warming up his K75 to mid scale on his bike and reporting to me it read 40 ohms.

Still not ready to pay about $65 for the sensor (come to find out the $65 sensor is the one with a short wire that controls the fan and the telltale, she's ready to blow, lamp. The sensor at the drain location is about $22), I rigged a variable resister I had between the black sensor wire and the engine block with two of the three binding posts on the resister so clockwise rotation would reduce the resistance from 100 ohms to zero ohms.

I turned on the ignition and the meter went to one quarter scale because 100 ohms was about the same as the defective sensor was reading when warm.

I then did what I thought Homer Simpson would do. I cranked the knob clockwise and counterclockwise over and over while saying "the needle goes up, the needle goes down" with each movement.

Replaced sensor. All back to normal.

I am happy to report that the sensor can be changed without losing more than one half a teaspoon of coolant. Either have a new washer or have someone at the ready to transfer the old washer while you hold your finger in the dike."  

 

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