1994 John Deere 1070 - thermostat problem? Or what else could it be?

[Swamp Fox]

While using my tractor my temp gauge was showing a normal running temperature, then suddenly showed a cold reading. My heater in the cab got cool. Full of antifreeze, no leaks, etc. Everything else seemed normal. Brought it back to garage and used my hand held remote temperature reader on the engine cooling system. The thermostat housing on top showed mid 90s degrees, below that on the block it was 115 degrees. It showed 100 degrees on top of radiator, 75 degrees on top hose. These were taken with the engine running.
Does that sound right? I cleaned the connection on the block heat sensor. When I shut the engine down the temp gauge needle goes all the way down, but then goes up to cold when I turn the key to start. The gauge started acting up when I had a bad battery connection on positive post. Is there a fuse that could have blown?
Thanks for any help or suggestions.

 

[RjCorazza]

Those temps you shot with the infrared thermometer are way too cool for an engine that should be at operating temp. I would suspect that the thermostat is stuck open.

 

[super55]

Agree with posts above. The thermostat died on you. Fortunately it did it in the open position. Should be an easy fix.

 

[Roadworthy]

Replace the thermostat. You can easily check a thermostat by watching it open and close in a pan of water heating on the stove.