Ford Explorer's Coolant Temperature Gauge Not Working? Here's a Cheap and Fast Fix!

That's the problem my elderly neighbor had with his 1996 Ford Explorer with the 4.0 L V-6 engine. He showed me his coolant temperature gauge, sure enough, his engine was warmed up and blowing plenty of hot air from the SUV's heater ducts, but the needle on the coolant temperature gauge was pegged solidy at "Cold" and wouldn't move no matter HOW long his engine warmed up.

My first question was: was his coolant level too low to register a reading on the gauge? So we quickly checked and found his radiator was full of clean, green coolant.

Possibly a bad fuse, then? Nope, that wasn't it either.

Must be the temperature sending unit, I theorized, a device that almost looks like a little brass sparkplug that screws into the top of this vehicle's near the thermostat housing. (Just follow the large upper radiator hose to where it goes into the engine and ...ta-dah..there it will be, just a little below and in front of the end of that same hose).

It has a little "L"shaped rubber cap, and a thin wire coming out of that cap. I unsnapped and removed the wire & cap, and then, using a 5/8" socket, unscrewed the sending unit and removed it.

In seconds the old sending unit was out and the new one was in, but first we took the time to wrap some white teflon tape on the threads of the replacement one to avoid any coolant leakage.

BIG MISTAKE! The sending unit had to "ground" to the engine to complete its electrical circuit, and putting the teflon tape on had prevented this. We started the Explorer up and watched the gauge...STILL not work any better to our disbelief!

After spending some more time in thought and analysis, and then noticing that the sending unit had only ONE wire and HAD to ground somewhere, somehow, the light went on in my head. Moments later, the (now clean and BARE of sealing tape) new sending unit was reinstalled...voila! Success!