My Temp. gauge is not working, it reads cold all the time. I just replaced the thermostat and the the temp sensor on the engine but it's still not working? Any ideas on what to do/check next?

 

Take the wire off the sensor and ground it to a clean bare metal spot on the engine. The gauge should swing all the way to one side or the other(I forget if it's cold or hot). Then take the wire off the metal and let it hang in the air, touching nothing. The gauge should swing the opposite way, full scale. Give it a little time, the needles are a little slow.

If the above test works, then the wiring and the gauge or ok. Make sure there is not a whole bunch of thread sealer on the sensor.

If the above test fails, then there maybe something wrong with the wiring from the sensor to the gauge, or something wrong in the gauge panel.

 

There are two wires on the sensor. Which one (color?) do I need to ground? I just replaced the sensor and I only put sealent on the threads

 

Grey/red wire is signal return and it also connects to 4 other components.

What did you use for sealant?

It needs a ground,

These newer vehicles are not in my realm.

 

I don't have my diagrams with me, but is there a chance you are looking at the wrong sensor? Usually you will have one for the guage, and have another for the fuel injection system.

 

Their is the vacuum air temp sensor in there somewhere too.

I found two references (6 pages apart) to a temp sending unit with two different colour wires.
What I already mentioned, and the red/white wire to the Temp sending unit.

Here's a diagram

 

I'm sure that I am looking at the right sensor because I went to the parts store and asked for the temp. sensor and they gave me the same one. Also when I removed it there was coolant!
I bet the second wire runs to the ground source!
I'll check it and let you know. Thanks for all the help.

 

Dragrazor,
It appears no one has clarified the fact that the temp sending unit is a ground out switch.You should have seen that in the diagram I posted above.

This means it's grounds through the metal case & if there is
"Too Much" sealant on the threads the case can't ground out.

It receives a signal of current and sends out a signal to different components.One of them being the gauge.

Also, you still haven't said what color the wires are going to the unit.

Please let us know.

 

Sorry guys, but the weather has been horrible lately. I'm gonna pull it into the garage today and I'll post what I find tonight.

 

I think you may be confusing the coolant temperature sensors. Your truck has two coolant temperature sensors. One is part of the engine control system along with the EEC module and a half dozen other sensors. This one has nothing to do with the temperature gauge on the dash. It has two wires going to it. According to my wiring diagram there is a yellow-red wire and a black-white wire. If that is what you changed it will have no effect on the temp gauge.

The other coolant temperature sensor( it was formerly called the temp sender or temp switch) is probably mounted on the top of the intake manifold. On some engines it is on the driver side near the front. It has one wire going to it--red with a white stripe. That is the one that goes to the temp gauge. To determine if the sender (sensor) is dead:
1. with the engine idling remove the solitary red-whitewire from the sender terminal.

2. ground the clip of a test light on the engine block and insert the probe inside the wire cap. If the gauge circuit is OK the light will flicker a little.

3. If it flickers replace the sender.

 

Rander,

I'm sure you understand why I have been waiting to hear what colours the wires are in regards to the unit he is talking about.

 

Mil1ion:

I know exactly what he is struggling with because about two weeks ago I had the same problem with my temp gauge and had a devil of a time sorting out the two different sensors. I normally can't quote what color wiring is. It is nice to be able to be helpful to others on the forum. I wonder why Ford changed from the old terminology to calling both units the same name.

Rander

 

The temp gauge sending unit only has 1 wire (terminal) on it.
The PCM coolant temp sensor has 2 wires (terminals) on it.
If you GND the wire on the gauge sending unit, the gauge
should go full scale to HOT.

 

I think Haynes made a mistake in that diagram. They shouldn't have the same name: anything for a gauge is called a "sender"; anything the EEC uses is called a "sensor" and usually has an abbreviation. In this case, they're the "coolant temperature sender" and the "Engine Coolant Temperature (ECT) sensor". Senders ground to whatevery they're installed in so they have 1 wire each. Sensors have dedicated signal & return wires so they have at least 2 wires (and often more).

Another quick way to remember is that the temp & pressure guages' wires are Red/White and White/Red, respectively.

 

Correct Steve, Thanks for chiming in.

That's why I have been asking for the colour of the wire/s right from the start..to know what it really is.