Temperature Gauge

[Seabass]

My temperature gauge keeps on saying it's overheating.. then it jumps back down.. then it goes back up to it's crazy state.. Does anyone know how to fix this? Like where to find the actual meter?
-Seabass

[anchovies]

Should be the sender unit's fault. It's located on the thermostate housing, smallest of the sensors on it, with one wire.
Did you open the cooling system lately? Air in the cooling system might do that too.