bouncing temperature gauge

the temp. gauge on my 95 Splash fluctuates between the middle and just a hair over the normal range but never goes to hot. i changed the thermostat because i thought that was it, but it still does it. what else could cause it? one guy suggested it maybe some temperature sensor on the bottom of the engine that may be faulty and another guy says it may be my water pump. i dont think it would be my water pump cause if it was, wouldnt my heater blow cold air instead of hot? it did when i had my Acura. anyone else have an idea or may know what it is. oh and i have plenty of antifreeze in it. the engine is a 3.0L v6. thanks for the help.

if it fluctuates quickly then its prob the temp sensor, if you do swap make sure your on the temp sensor and not the oil pressure sensor. Usually the water temp sensor is on top or top side of the engine in a water passage.