Good day!

We have a diesel mitsubishi adventure. Recently, napansin ko na tumataas yung temperature reading ko sa guage during traffic. normally it stays sa half-level lang with AC on. di naman kumukulo yung tubig sa reservoir (50:50 coolant mix) and i already flushed the system last week. tumataas siya ng 3/4 sa guage during traffic, nakakakaba lang kasi baka mag-overheat. pero sa highway ok naman yung reading, slightly above the halfway mark. ok naman yung radiator fan clutch, may resistance naman kapag pinihit when the engine is cold. medyo malabo yung chance na mag-overheat basta basta since i only drive about 10km to my workplace.

Then, i discovered one morning upon starting the engine. while waiting for the diesel to warm up, i noticed the temp guage rise to 1/4, the key in the "on" position.

this puzzled me since the engine wasn't even running yet, and the temp gauge already rising up . any ideas on whats wrong with my ride? could it be the temp sensor? or the gauge itself? if so, where could i find the sensor?

TIA.