Water temperature gauge doesn't work. Assumed the problem was the sensor so bought a new one. Installed it, still nothing registering on the gauge after I know the water is heated up (drove it for 45 minutes, heater blowing hot).

So crossed the ground on the sensor and the gauge shot to the top so gauge is working.

Pulled wiring diagram and that sensor is SUPPOSED to register 79ohms for cold and 8 ohms for hot.. So bought a 10ohm resistor from radio shack and attached the water temp lead to it and the gauge read correctly about 1/8 inch from the H mark on gauge. This confirmed for me that gauge is not at fault.

Next I attached the ohmmeter to the sensor itself, boiled some water, placed the sensor tip into it and it read 86 ohms, in freshly boiled water! So at boiling the sensor isn't anywhere near to tripping the gauge to even start reading cold! So I tested the old sensor that I was replacing and in boiling water it shows 94 ohms?

What am I doing wrong, is there an assumption I am making here in error? I want to conclude the new sensor is bad, but the old sensor reads nearly the same reading under same conditions.So yes maybe they are BOTH bad but that seems to be pushing probability.

If it matters this sensor is the type that is inline from radiator to heater core, not the type that is in the engine block, at some point ford changed their sensor setup but didn't change the schematic drawing. Which doesn't matter the only difference is the one in-line has a ground wire to it rather then grounding off the engine block.

Vehicle is a 97 Ford Ranger with the 2.0 liter engine.

 

Simple solution, get new sensor from the Blue Oval Parts, i.e., Ford.

 

the temp gauge of my '94 showed 1/4 way up and engine cold. didn't notice at first since the truck is new to me and previous owner didn't mention.
I checked the connections and found corrosion on the block sensor. cleaned all with steel wool and fixed.

 

Check to make sure the wire is making a good tight connection.

 

Check the ground.