Temp Guage Fluctuates

[argoose]

hi,

having problem with coolant temp gauge, warming up as normal, but then drops back to 1/4 raises back to half does this for 10 mins then after it drops just below half and back again, does this constantly.

never goes more than a fraction over half, fan works fine, heater output fine, new sensor new rad/expansion cap (same syptoms before changed them), not lost any coolant since coolant flush, change before christmas.

I changed thermostat when I changed coolant, working on theory that just because it's new dont mean it's good, that's my next point of call.

Any other help will be gratefully recieved.