92 Civic: weird thermostat gauge prob

Ok, I have a 92 Civic CX HB, rebuilt engine @dealer (same specs).....and only a few months into this rebuild, the temp gauge on the panel "flutters" down, mostly on curves, going uphill, & acceleration. It will also move downward with no reason at all, esp when in the first 20 miles of driving.

It has done this before the rebuild off & on as well. Now: much more "on."

Now there is NO upward movement, ie 'another blown head gasket.....'

Having said that, if I put the vent fan on, the gauge is perfectly normal! (no a/c, just a vent).

Do you think it could be a ground problem? Or a sending unit going bad? Something in the electrical bundle with the fan doing "something?"

Beats me! Anyone else have this happen? What can I check myself?

Mechanic said take it to the dealer, but I bet they will carry on about another major undertaking! Car runs perfectly well otherwise, no coolant loss, oil fine, etc.

Thanks for your imput!:smokin: