Temp gauge not reading accurately

Pictured below is what my 97 4.0 is running at versus what the gauge is reading. The sensor is only a couple months old and is a brand new Mopar sensor. I had a store bought sensor that read just a little higher. How do I fix this to get the gauge to read correctly? Is the old wiring causing the extra resistance leading to the hotter readings?

Is that Actron gun accurate?

See if you can get a scanner that reads live data and check the coolant temp before running the engine (overnight cool down). Remove the radiator cap and, using a digital thermometer (meat thermometer), check the coolant temp. Compare the two readings.

The exact number does matter. The dashboard gauge are not scientific instruments, they are just indicators, warmer/colder than normal, or higher/lower than normal. Your Temperature Gauge indicates the normal 195*-215° zone in which all Jeep 4.0L operate. The Temperature Gauge is close enough to an average XJ that there is nothing to fix or adjust. If the gauge leaves the normal zone of indication that is typical to your XJ, it will still advise you that it is warmer or colder than before.

If you really want to monitor the engine data, find one of those OBD-II data readers like the ScanGuage 2 that will display real-time info from the PCM.

Read this -> http://www.naxja.org/forum/showthread.php?t=1029024

Sidewinder CC said:

Is that Actron gun accurate?

See if you can get a scanner that reads live data and check the coolant temp before running the engine (overnight cool down). Remove the radiator cap and, using a digital thermometer (meat thermometer), check the coolant temp. Compare the two readings.

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I would hope the Actron gun is accurate, I borrowed it from a Tech at work, I work at a dealer. I showed him the picture and he handed me a scanner to use to compare.

On 97+ the gauge is fed by the sensor in the housing. So check the OBD2 coolant temperature and see what it shows for the sensor value. If its close to the IR gun then the gauge is wrong. But if the sensor data is off, you might have a bad sensor.

Sorry for the typo above: The exact number does - not - matter.

Gauges are not a calibrated, expect some variation from one to another.

Ok, I work at a dealer in sales so I got a tech to let me borrow his Matco scanner that would read live Data. The exact value got up to as high as 223 at one point. And the readings of the gauge seemed to fall right in line with the scanner.

The entire coolant system is new as of November of last year when I put in a new engine with the exception of the CSF radiator that was new 3 months prior to the engine giving out. I have a new replacement radiator to rule out a defective radiator. The tech and I have been catching our head because every single component of the system including the sensor has been replaced. The Sensor is Mopar to insure accuracy. He asked if the fan clutch was replaced and I said yes but it was a store bought Duralast and he suggested I try a Mopar fan clutch.

Tim_MN said:

The exact number does matter. The dashboard gauge are not scientific instruments, they are just indicators, warmer/colder than normal, or higher/lower than normal. Your Temperature Gauge indicates the normal 195*-215° zone in which all Jeep 4.0L operate. The Temperature Gauge is close enough to an average XJ that there is nothing to fix or adjust. If the gauge leaves the normal zone of indication that is typical to your XJ, it will still advise you that it is warmer or colder than before.

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This. You can't count on those gauges to be spot on. Get use to where the needle normally resides and make note of it when it's not normal.

Ben824 said:

The exact value got up to as high as 223 at one point. And the readings of the gauge seemed to fall right in line with the scanner.

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So what exactly is the problem?

Given what you say about the scanner matching the gage, if the IR gun is accurate, I would think the variance is in the sensor. Having said that, like the man said, they are pretty much to show when things change, not the absolute temp.

Note the number of divisions (4) on the left that represent a total of 110 degrees, but on the right side look at the number of divisions (4) that equal 150 degrees. No where close to being linear.

After installing a new motor, i could not get an accurate sensor reading with the stock gauges, went with autometer stuff and it is much more accurate. Shocker, i know.

Id figure out whats "normal" for that jeep, then whats "hot", then give yourself that mental redline so to speak.

If the sensor reading is different from the IR reading, then either the sensor or the IR gun is defective

Ok so for a little reference for a lot of people so they understand my concern, I have been with this Jeep for 14 years. Never has this ever been normal. I have had 4 coolant sensors on this Jeep. 3 Mopar sensors and one store bought. The first two went bad and stopped reading entirely. I went cheap the second time and got another one from Advance. During this running hot issue I replaced everything else so I put on a new Mopar sensor to rule out a cheap inaccurate parts store sensor. The Mopar seems to read a little less but not by a whole lot so the store sensor may have been reading a little high but by only a few degrees. This has never been normal readings for this Jeep. I have run this exact same cooling setup on this Jeep in the past and it consistently ran less than 210 on the gauge and stayed that way for 7 years until that old CSF sprouted a tiny leak. I swapped in a 2 row Champion all aluminum radiator that lead to 8 more garbage cheap aluminum "performance" radiators that all went bad and violently leaked. I dealt with that for 4 years and then put this CSF 3 row replacement on. I had it for 3 months before the original engine went bad and it still ran hotter just like it does now. Now the difference now between what I had back when I had the first CSF radiator that was good for 7 years is I have a parts store fan clutch and not a Mopar one. The tech and I have talked and he last suggestion would be to get a better quality Mopar one.

Any other mods? My temps started getting out of hand after I installed a winch

ehall said:

Any other mods? My temps started getting out of hand after I installed a winch

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Right now I don't even have a bumper so there is zero blockage. I checked the condenser and doesn't have any blockage either. The only mod really is I have ditched the in radiator trans cooler to and auxiliary B&M cooler that sits in front of the mechanical fan.

Not that it helps, but I put in a 2 row CSF radiator 2 years ago and have been running a little hot, then pretty cold til I put the ac codenseor in for some blockage

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Ben824 said:

I would hope the Actron gun is accurate, I borrowed it from a Tech at work, I work at a dealer. I showed him the picture and he handed me a scanner to use to compare.

Click to expand...

Remember that you are reading the "average" temp of anything within your DTS ratio !

cody4359 said:

Not that it helps, but I put in a 2 row CSF radiator 2 years ago and have been running a little hot, then pretty cold til I put the ac codenseor in for some blockage

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Click to expand...

Replacing the AC condenser is next after putting in a Mopar fan clutch

I have triple eletric fans and no AC, just the condensor. Think my transmission is why it gets on the warm side up grades and for the cool side, I'm betting it's the hesco hi flow housing and the fact I have a more efficient radiator, as well as maybe having my fans kick on a little early

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