90 Shadow Temp Gauge issue

I have a 90 shadow with 260,000 km on it...2.2 L, Auto. The issue I am having it when I turn the heat or cool on with the fan (at any setting)my temp gauge moves to the top of the HOT reading. I am not turning on the A/C just the blower.

As soon as I turn it off and slide the temp gauge to the left (recirculate) it goes back down to a normal reading (about 1/3 of the way up)...

Any ideas?

I dont think that you will over heat i think that its a problem with the guage. Just wo to a salvage yard grab one they arent that expensive and trow it in see if it makes a difference. If not you should take it to a shop to have it looked at.

my '90 shadow had a similar problem. it wouldn't go all the way to hot but would go high when using the fan and go down when it was shut off. it could be a grounding problem, a short, a bad gauge or temp. sensor.

i noticed it after replacing my water pump but that is probably unrelated. good luck.