Your temperature gauge isn't really a gauge - any time the engine
temperature is in the range of about 80-110 C it will read in the
middle. When it goes above or below this, the gauge will move quickly
away from the middle. So my guess is your thermostat is failing, and
the engine temperature is hovering from the cool side of normal to
slightly below normal. Change your thermostat, this will eventually
turn your check engine light on.
