Tempature gauge going crazy

[Zyros]

Hey, my GF's car was having issues today.

The temp gauge would go up to hot, then within a minute down to noarmal, then up to hot, then down to noarmal etc..

When it was on Hot (red) i popped the bonnet and the engine seemed to be at noarmal running tempature..

Radiators sweet, no cracked hoses and coolant levels sweet.. Any idea's?
I was thinking either then Fan (if it would do that?)
Temp sender
Theromstat?

[Calvin]

faulty thermostat/temp sensor id say.. going on the assumption your observations are correct and motor is sweet

[gepsk8]

what car?
when u check the coolant last before the problem?
sounds like it needs to be bleed up propably get the air out of the sytsem

[MrOizo]

check that the wire is actually hooked onto the sender and its not grounding anywhere else..

[Zyros]

Honda civic 1993 sedan,
It deffinatly not over-heating, i thought if it was the theromstat, the car would actually overheat?

[gmacrae]

or just bubbles in the system?

to burp the coolant some cars want the front raised up a bit, then idle with the cap off for a while, tapping the gas a bit, if you notice the level goes down there was a bubble in there - could explain it.

[sergei]

hondas have special nipple to remove air from the system on the coolant elbow on the head.