Bad Temperature Sending Unit?

[kbsmith_48]

My 94 explorer's temperature gauge has been erratically changing position. It will go form the N to the R bounce a couple times before dropping near the C then rapidly rise back to the N. When the truck is at operating temperature and the Key is on but the engine is turned off the gauge will still fluctuate Is my sending unit going bad or is this another issue? I have re-bled the system and the coolant is full.

Can I put a manual gauge or electric gauge on it and if so how?

 

[Anime]

It could be the temp. sender, if so it's a fairly inexpensive part and easy to replace. You might also want to visually inspect the temp. sensor and the wires and connector attached to it, it could be that the connector is loose or age has caused the wiring or connector to degrade.

If the gauge needle actually bounces and changes position rather quickly, the problem could be the gauge itself, or the instrument panel.

If the needle just changes position slowly, it could be a faulty thermostat. Usually when a thermostat fails, it starts closing up or even closes completely and the engine temp. shyrockets, or some thermostats fail by staying open and never letting the engine warm up, but thermostats can also fial and wind up opening/closing according to coolant flow and factors other than temperature. This is usually the case with super cheap thermostats that use thin, weak springs and low quality materials. Stant's Superstat is a good choice for an inexpensive yet good quality aftermarket replacement.