156 1.8TS Engine Temp/Coolant Issues
I recently bought myself a 2002 156 1.8TS Veloce. Have been pretty happy with it so far but a few little niggles are worrying me. About a week after buying i noticed the coolant tank was almost completely empty, so i filled it up to max. Another week later i checked it before a long journey and it was empty again. The engine was warm so i slowly undid the coolant cap. As the pressure released, the coolant level filled back to normal. I'm certainly not an expert on cars and concluded that perhaps this was normal if the engine was warm. Took the car 500 miles up north and back without any trouble (and a decent 42mpg average), checked it again when the engine was stone cold to see the coolant tank almost empty again. I cannot see any evidence of leaks anywhere and if i wait until the engine is warm and undo the cap, it refills as before.
In addition, the last few days my temp gauge has been heading north of 90*C a few times. Earlier today i was sat at traffic lights and in the space of a minute the needle went from 90 to over 110, yet within maybe 6 seconds of the lights going green and me getting up to speed, it shot straight back to 90. I'm sure this can't be accurate. The speed with which the needle moves up then back down is ridiculous, yet if i'm not stuck in traffic it generally hovers just under 90 quite consistently.
Grateful for any suggestions anyone may have. Besides this issue the car seems to run well. Doesn't sound like a bag of spanners and returns some impressive MPG figures to boot.