I rebuilt the 2004 Dakota 4.7l after front end damage.
New water pump, tstat, clutch fan, electric fan and radiator at the time.
When the truck ran with the original sensor, it seemed to get up about 3/4 way and creeping up.
Using the digital gauge, nothing is hotter than 205 degrees.
I replaced the sensor and it's gotten worse. Everything is still no more than 205 degrees, but the gauge runs up to full scale as it hits operating temperature.
I know it's not over hearing and it all seems okay. The electric fan will come on with the ac, so I know it's working and I'm pretty sure it comes on as needed based on the temperature.
I did the resistance check to both sensors and the both seem within specs that are in the manual.
I tried resetting the gauges with the trip button held and everything went through the paces.
Is there something that needs to be recalibrated somewhere or maybe at the ECM?
I thought if putting a real number gauge in to monitor the actual temperature, but that won't help to provide the ECM with the proper information to control fuel and such.
I'm stumped.
Please help.

 

Need to plug in with a scanner, and see what the PCM thinks is going on. You may just have a bad gauge.....

 

Agreed. Put one of those bluetooth scanners on it and read the temp as you drive. Hopefully you bled the cooling system real good... best done with front end high up. Also, what type of radiator did you put in?

 

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I used the scanner to monitor the temperature per the PCM and both it and the gauge read higher than what my digital thermometer says.
I swapped back to the original sensor and while it does seem to read slightly lower, the readings were still higher than what my digital thermometer is saying. The thermometer reads no higher than 245F. Mostly lower than that. I found that reading in one location on the block. The tstat housing, hoses, sensor and where the sensor plugs in and the radiator are significantly lower.
I would have no problem driving it and knowing it's not running so hot, but I'm concerned that the PCM is getting the wrong info. It switches the electric fan on and will set the check engine gauge when it gets high enough.
Unfortunately the 3/4" socket I used to remove the sensor doesn't fit exactly and they get stuck, so the new sensor got broken while trying to remove it from the socket. It has a lifetime warranty at AutoZone, but probably not in this condition.
I'm thinking since those two sensors did measure different from each other, but within specs, that I could try another one and hope it is calibrated differently.
I paid $32 for that new one, thinking the more expensive one would be better.
Looking online, I can find them ranging from $7 to $35, but the cheap one is double when shipping is added on.
What I am wondering about is if the PCM can be programmed wrong and interpreting the sensor as being too high.
I don't know if that is even programmable.
Except to keep throwing parts in and hoping for a different result, I'm stuck.
I hate to take it to a dealership just for this issue.
Side note, I had a transmission problem, it was rebuilt, but also required a new computer. I bought one that was calibrated to my Vin. The transmission problem was corrected, but I wonder if maybe this was programmed wrong. I guess I could call that company to ask.

 

Might consider spending the money, and getting a genuine Mopar sensor.... That is far more likely to be more accurate.

The temp sensor is just a variable resistor by temp. As temp goes up, resistance goes down. (If I remember right) Dodge has specifications for what values at what temps that should be, and that is programmed into the PCM. It is FAR more likely you got cheap sensors, than the PCM being out of spec.

 

As Heyyou said, the calibration is internal to the PCM. I don't believe it is in a tune-adjustable field. The only true way to know is to put a second sensor in line with a separate monitoring gauge.

An infrared gun can have a big margin - There can be 10 of us on a starting line and all 10 will read differently. NHRA's gun reads 20 degrees higher than ours, so when they call out temps, i have to account for that in how we set up the car. They also read highly errant on "bright" materials like brass and aluminum. The way that parts shed heat also affects what the gun will read.

My truck has the 408 block half-filled (meaning the coolant passages are filled 50% with molten-then-hardened powdered iron strengthening compound) and still cruises at 200-210 degrees, which is perfectly acceptable persistent temperature for iron block / iron head. The entire engine only holds 1 gallon of coolant, and the radiator holds 3 quarts - the radiator is 11" tall and 20" wide to fit the AC condenser and intercooler.

So either the parts store sensors are very wrong, or you have a very inefficient radiator.

 

I recently checked compression and all cylinders are about 150lbs.
I did find two bad ignition coils on cylinders #4 and #8.
Replaced them and engine runs really smooth. (See another thread where I discussed and put video on the forum under Virg23)
Here is the latest video outlining the issue. The gauge is the only thing saying it's too hot, every other method suggests it is running cooler.
I made a YouTube post on this video.

 

Bad sensor. 257 is TOO HOT. But, since the engine isn't really that temp...... gotta be the sensor, or the wiring. I know you have replaced the sensor, trying getting a different brand, or, better yet, get one from the dealer.

 

I have an OEM Mopar sensor on its way.
It sure seems to me that the sensor is the only thing telling the computer, which logs it and sets the gauge.
I can't think of anything else that would be involved.
Except possibly a thermostat that is opening at too high a value. It should be a 195f based on what I took out.
Perhaps it's not opening enough, but it just doesn't seem like a hot running engine.

 

If the top of the thermostat housing is only 190 something, then the thermostat is doing its job. Gotta be a bad sensor.