Doesn't get hot or overheat.. no bubbles in rad or oil. Goes from the 1/8 to half and down then back up.. not like every second but about every min or
Make sure there is no air on the system.
Ed
A new t-stat sure wouldn't hurt. If its not a "instant" move on the gauge I would just change the stat to start.
You should also check all the hose connections. Years ago I had a Sable that developed an erratic temperature gauge. It also lost some coolant over time. Eventually I figured out I had a high pressure leak. Whenever the car got to a certain water temperature (and therefore water pressure) some coolant would force its way past a hose clamp connection. This would effectively lower the pressure in the system, allowing more coolant to boil off, which immediately (but briefly) lowered the temperature in the system. I finally located the leak by the white residue the leak left at the leaky connection. In my case it was at the radiator. The original spring clamp on the radiator had been replaced with a worm gear clamp. This had been over torqued and warped the plastic radiator fitting.
Ed
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