Weird temp gauge behaviour

[FFMan]

1994 Griff 500

Been ok recently but went out the other day and as it was idling when i shut the garage etc i noticed the temp gauge stayed low, and then after a few mins, rose in front of my eyes to just on the red, but the fans didn't kick in. Then it just as suddenly dropped to normal.

Shrugged and took it for a short drive, and every 3 or 4 mins it would do the same, temp gauge suddenly rises and then a few secs later drops to normal.

So Sunday i topped the expansion tank from one third full to two thirds, fired it up and it did the same. No obvious leaks.

The only thing related is a few weeks ago it broke the pre-serp fan belt and it got hot quicky, but powered it off and coasted to the road side Didn't feel like it was a bad overheat, and i think it has been ok on a couple of drives since.

I guess i'm think stat is fubar but all suggestions welcome.

If its stat, anything special to note, what temp do people go for.

thanks

[Super Sonic]

I would also suspect thermostat, I've had similar symptoms in a Civic and replacing the thermostat cured it.

[Belle427]

Belt not slipping is it?
Did the old belt snap?

[FFMan]

Old belt snapped - first drive after winter snooze

i'll check the tension on the belt - could be the issue

[Phud]

Check the temp sender wire, if the belt damaged it, it might display spurious readings