[14theroad]

Lol we are a bunch of squirrels...first thing we notice is the fuel gauge. Anyone notice the temp gauge is pegged?

I did a quick search to confirm my suspicions. There are two sensors actually on this vehicle. One for the cylinder head temp that sends its signal to the PCM and a coolant temp sensor. My mustang has the same setup as do most newer cars.

A Cylinder head sensor is typically used for PCM input and controls because it's considered more accurate about real-time engine temps that are critical to timing events and A/F ratios.. I've never seen it used for a dash gauge reading. That's what the Coolant temp sensor is for most likely in this case. .

I dug a little bit more and it turns out the cooling fans are controlled by the ECM which means it's more than likely the Cylinder head temp sensor is what controls the fans.

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The coolant temp sensor is most likely just for the gauge. It's a two wire sensor so it's really easy to test. At room temp it should have a very low resistance. That resistance goes up as the sensor heats up. That increase in resistance is what is translated as an increase in temp on the gauge. So, in theory, if the sensor is bad and pegged the gauge as it is, the sensor will have a very high resistance and not change as the engine warms up.

If you remove the sensor you can test it just like you would a thermostat. Take a volt/ohm meter, Test the sensor at room temp, then drop it in some very hot water or boiling water and watch the Ohm reading on your meter meter, it should go up. If it doesn't budge then you have found a bad sensor.

Another way is if you have access to a handheld OBDII scanner with Live data, you can view the engine PID for the engine coolant temp. The PID will use the Head temp sensor for that reading,so if the guage is pegged but the temp in the handheld says otherwise, you will can investigate the coolant temp sensor and circuit closer.

 

[14theroad]

To be clear, which sensor did you replace? You mention a coolant temp sensor in one instance (aka ECT) then mention a HTC (should be CHT) sensor in later on. Engine Coolant temp and Coolant Head Temp sensor are not the same.

The ECT is located on the engine near the high pressure fuel pump on the drivers side of the engine.
The CHT is located on top of the motor /valve cover area or on the backside of the head.under the valve cover area.

If you go to Rock Auto you can see the physical difference between them. The CHT is much longer and narrower than the ECT.

Found this in my search. Interesting, it's counter to how I'm familiar with these sensors working on most cars but this guy is a ex Ford master tech so it's worth checking out. It's a 2.5L non turbo motor but false overheat issue is identical to what you are experiencing.

 

[14theroad]

At this point, I would stop and take it somewhere to have it diagnosed. Electrical issues can be a real PITA unless you have a very good understanding of how a vehicles particular system works. The basics are the same but the interactions between the sensors, the gauges and the PCM/ECM and other intricacies vary from manufacturer to manufacturer and even model to model.

$120 for a diagnosis vs a potentially infinite money parts cannon.