Erratic temperature gauge on JD 5105

[Floater]

Starting a couple of weeks ago, the temperature gauge has both slowly, and rapidly, increased to hot and "needle pegged" with no apparent over-heated engine. Gauge shows warm up as normal, runs normal for awhile, then suddenly shoots upwards. I have flushed and refilled cooling system, installed new thermostat, replaced temperature sensor/sender unit. No change! The gauge, when temp sensor wire is grounded, goes to full hot. Also, the gauge sometimes does not go all the way to off-peg when ignition shuts off....it may stop 3/16" off the peg....but not always. I have not pulled the water pump, as it seems not to be a circulation issue. Any thoughts?

 

[JD5210]

It could be a grounding issue. I purchased my 5210 used and when I first got it, the temp gauge was jumping around some. What corrected the problem was when I cleaned the negative battery connection, where it connects to the frames.

You may already know this if you connect wire from temperature sender to ground. The gauge should indicate HOT.

 

[Floater]

Thanks! Easy to check (and cheap!). Let you know....

 

[Floater]

Thanks! Easy to check (and cheap!). Let you know....

Yo! Took ground apart and sure enough, although it looked good from outside, bolt threads were rusty, as was threaded hole in frame. Cleaned, greased, reassembled: First improvement is the engine cranks over faster!! Thanks for that! No verdict yet on gauge: it ran under load for 10 minutes and acted normal, but thats not definitive. Will report upon further useage. Thanks for the tip....