Temperature gauge quit working after changing the thermostat and coolant.
Followed advice on this great forum, and also the procedure in a repair manual. With the engine off, I disconnected the single wire from the temperature sending unit, and switched on the ignition without starting engine. The gauge pointer stayed in at the Cold mark. Using a Jumper wire, I grounded the sending unit wire and the needle on the gauge went to the Hot mark. I quickly turned off the ignition, and replaced the sending unit with a SW-2328 (F1SZ-10884-A) Temp Sender. Warmed up the engine, but still no reading on the dash gauge. Any thoughts and ideas greatly appreciated.

 

Need to identify WHICH engine.

 

Did you remember to reconnect the wire back onto the sensor after your test?

 

460 gas engine,
Yes, installed new sensor and wire is reconnected.
Maybe Ford sold me a bad sensor?

 

Stranger things have happened.

 

Promising lol

Can the sending unit be tested for proper resistance? Voltage?

 

Yes and yes. Resistance is easiest.

First, make sure you didn't use Teflon tape when installing it. That insulates the threads and causes the sensor to appear open (no gauge movement). Measure sensor body to the block to ensure continuity (zero ohms).

Measure sensor resistance (cold engine). Report ambient temp and the resistance.

Warm up engine to operating temp. Re-measure resistance and report results.

 

Yes, zero ohms sensor body to block.
Cold at 80 degrees outside, the Ford unit reads 200 ohms.
An aftermarket NAPA TS7245 reads 180 ohms.
Warm the Ford unit reads 100 ohms. Napa unit reads 80 ohms.
The Napa unit came with teflon tape on it. I'm going to remove the tape and install the Napa unit, hoping it will read better than the Ford unit. Any thoughts regarding what to do next? I'm thinking possibly an aftermarket gauge set-up.
Best regards.

 

Update on the temperature sensor. I put in the aftermarket NAPA sensor.
Now after the truck warms up, the gauge does move over slightly to the very edge of "Normal" just to the right of Cold. I'd really like a better idea of the temperature, especially when towing something. I bought a Sunpro temperature gauge kit and am going to tackle this when I'm home again for a week. Thanks again to all who posted their questions, ideas, etc.