Temperature gauge mystery

[sno-kart]

We finally got our motor running (liquid cooled two stroke from a snowmobile) but are having a strange issue. We replaced the temp gauge which came on the snowmobile because it was broken and bought a new one. It's a simple probe that has wires going to the digital gauge. It works perfect and displays the coolant temp when the engine is off... but as soon as we start the engine, it goes on the fritz. It stays on, but it displays 0's one second, then it shows 262 deg (max reading), and the brightness of the gauge fluctuates. As soon as we shut the engine off, it shows the correct temperature. We thought it might have had something to do with the battery so we hooked the gauge up to a completely different power source separate from anything else on the kart, but had the same result. Any ideas for why this might be happening? Thanks!

 

[hardrock21]

Did you replace the temp sending unit when you replaced the gauge? Sounds like a grounding issue.

 

[mckutzy]

Maybe there Is an electrical interferance influencing the reading?

 

[sno-kart]

Did you replace the temp sending unit when you replaced the gauge? Sounds like a grounding issue.

We used the sending unit (the probe) that came with the gauge. Again, it works fine when the engine is not running and freaks out whenever the engine is on.

 

[realfast89gt]

Sounds like interference, maybe you have a resistor plug and could try non-resistor? Or grounding is possible also, but with those symptoms it would have to be a blatantly loose ground and would be easy to find if so.

 

[Doc Sprocket]

Sounds like interference, maybe you have a resistor plug and could try non-resistor?

I was going to suggest the exact opposite... Either way, I must agree. If an isolated power source did not solve the issue, then you're down to one of two things- interference, or a defect being affected by vibration.

 

[hardrock21]

I'd start by back probing the temp sending unit with the gauge not attached. Measure the resistance as the sensor is heated. I would leave the sensor attached to the engine rather then bench heating it, in case it's grounding trouble through the block. My guess it that the resistance will decrease with heat and increase as it cools (as it should.) But, doing this will eliminate any trouble with the sending unit itself and will confirm that it's a gauge issue. You can manually test the gauge through the range by adding resistance to it with a potentiometer. If all things are fine there, it has to be trouble with the power going to the gauge, so back-probe the power wires and read the voltages being put to the gauge when the issue is happening. Try shielded wire and be sure to route the wires away from interfering things, i.e. coil, ignition module, etc.

Paul

 

[sno-kart]

Thank you guys. We are going to look into interference and grounding issues on Saturday and we'll report back with what we find then.

 

[fowler]

If its intermittent like that's I'd be calling Brocken/crushed wire
Or a loose pin

If it works great until u add vibration