Buick Century Limited, 1989, 3.3, 300.000km.
Starting cold, temp needle going up to middle (105F) and then suddenly,
going down to 1/4 of the range, and from there it will going up and down
between 1/4 and middle of the gauge till it stabilize over time to middle
between 1/4 and 1/2.
Cooling system full, plenty of heat in car, when it happen, less heat is
coming but will eventually get warmer with the needle rasing again.
Radiator fan is working if this matters.
Any clue? themostat perhasp?