JD 4310 temperature gauge problem

[RockyDeere]

My 4310 temperature gauge pinned high; Replaced the thermostat, removed the water pump and tested (perfect) as well as the fan belt, radiator, air filter etc. When idlling the temperature gauge climbs to pinned when the sender is reading 507 ohms. The water temp measures 107F at the threaded plug next to the sender on the head side of the thermostat! ....the manual indicates 40-700 ohms as range but no curve or reading. 2 dealers have no idea. Has anyone seen a gauge go bad reading high temp?? Looked over wiring with all covers off and found no signs of critter damage (evicted a few this winter)... has anyone been here before?? Opened up the gauge and found light traces of gray film inside white back cover, but looks okay... Thanks.

[arrabil]

The 42/43/4400 series had a lot of bad instrument clusters. Mine currently does what you're describing. Might be the same problem with the 4310...

[K7LN]

When idlling the temperature gauge climbs to pinned when the sender is reading 507 ohms. The water temp measures 107F at the threaded plug next to the sender on the head side of the thermostat!

That would be a ball park figure for sender resistance at that temperature. To pin a gauge, you'd have to be around 25 ohms or less. I gather that things start out OK, but then the gauge reading starts to climb.

What happens if you remove the sender wire while it's pinned and the engine is running? What happens on a cold engine when you turn the key to RUN without starting, and let it sit that way for 5 minutes?

It would be nice to see the schematic of the gauge circuit to judge things better. Going by the above comment and your resistance reading, I'm thinking gauge problem also.

[RockyDeere]

Thanks arrabil & K7LN. It turned out to be a bad instrument cluster...took it apart and cleaned all parts, and resoldered several connections. It the ran right at correct temp...then pegged...a good sharp rap temporarily corrected that. Best guess is a short in the windings in the gauge due to vibration. They didn't wind and terminate tightly, maybe due to flex inherent in that assembly - to avoid stress breakage. Will replace if not too obscene or will have repaired.

Wiil update if that is not a final solution. Thnaks again for the quick response.