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Temp Gauge Reads High With New Senosr

DXJ

NAXJA Forum User
I busted off the plastic connector on my original coolant temp sensor in a ham fisted moment. It's the one at the back of the head that runs the gauge. I have now replaced it with two separate new sensors and both of them read about 15 degrees higher than my factory unit. Is this common? Is there a specific sensor that reads like the factory unit? I understand I can just get used to the gauge reading closer to the redline than it has for 28 years but I'm a creature of habit and would like it to read what it used to. Nothing else has changed and the engine runs thermally just like it did before I broke the sensor off.

1995 Cherokee Sport, 4L, AW4, NP231...
 
You could also check the old sensor vs one of the new ones in some boiling water and a ohmmeter !!!
 
I busted off the plastic connector on my original coolant temp sensor in a ham fisted moment. It's the one at the back of the head that runs the gauge. I have now replaced it with two separate new sensors and both of them read about 15 degrees higher than my factory unit. Is this common?

Don't know if it's common. Tried two sensors on my son's '95, and it still reads ~15* high as well. Checked temps. with a point and shoot IR thermometer and the actual temps verified the error at the gauge. Tested the thermometer, and it is accurate.

Do agree with RCP, testing the sensor is something that should be done. I'm lazy, or busy; can't decide.
 
The factory sensor snapped in two and i discarded it. So I can’t compare to it directly. A while back I did use a gun to compare some areas of the engine/cooling system for kicks and the gauge read similar to what the gun read. I had verified relative accuracy of the gun using a piece of steel in boiling water.
 
What is it reading? Mine, like every xj I've ever owned usually rides a hair before straight up 210, unless I'm crawling in traffic. Which is about 15 degrees over the 195 thermostat where it probably actually is running.
 
What is it reading? Mine, like every xj I've ever owned usually rides a hair before straight up 210, unless I'm crawling in traffic. Which is about 15 degrees over the 195 thermostat where it probably actually is running.

That's exactly what mine used to do and what I'm used to. But stupid me broke the sensor and now the two replacements I've tried both ride a little over 210 at best and go up from there to near "orange" when it gets a bit hot and the auxialry fan kicks on. It reads constantly now where the auxilary fan used to kick on. The auxilary fan sensor is normal so it doesn't kick on now until the gauge reads close to orange.

Is there a brand of senosr more likely to read like factory? One of the high reading one's is Crown. I do not know the brand of the other high reading one.

Anyone know who made the factory sensor?
 
Just some more data for those that care. A third sensor (Standard brand) reads even higher than the rest. So the closest so far is Crown which reads about 15 degrees high.

According to my verified temp gun, the thermostat is opening right at 195, or as close as I can realistically measure externally. The area the temp sensor screws into reads just under 210, but the newest gauge (Standard) reads around 225-230. My factory gauge sensor used to read just under 210 under these same conditions.

Giant air pocket? Just grasping at straws. I wouldn't think an air pocket would as so consistent as I'm seeing.
 
What is it reading? Mine, like every xj I've ever owned usually rides a hair before straight up 210, unless I'm crawling in traffic. Which is about 15 degrees over the 195 thermostat where it probably actually is running.

I'll answer this better this time. For 28 years, my gauge has read slightly under 210 when things are stable and it's generally cool outside. If it's hotter outside and I stop at a light or are in stop and go traffic, it would climb to just over the 210 mark. Another millimeter or so to the right and the auxiliary fan would kick on. I understand that this is higher than the thermostat but the back of the head that the sensor screws into, seems to be consistently higher than the front of the head where the thermostat is.

The Crown sensor rides just under halfway between the 210 mark and the next mark when everything is stable and running normal. The Standard gauge sensor reads just over half way between the 210 and the next mark. The aux fan is not kicking on because the sensor that runs it seems normal.
 
I bought my XJ used. Whether it was the temp sensor that was installed when I bought it or the one I installed, its consistently ready 15F higher than the tstat opening temperature.
 
I also bought mine used and the temp sensor rides approximately 210+-, except when warming up.
At warm up, it reads up to half way from 210 to the next mark to the right for a moment, then calms back down to 210+-. Every time.
I have assumed this is normal and a delayed response to temperature since the sending unit is farther down stream than the thermostat.
Is this assumption correct?

Also, does the factory replacement sending unit also read high? The replacements above are not factory (I believe)
 
First, year is a factor because the temp sensors are mounted in different locations thus different readings! Second the actual motor temp is different than the t-stat rated temps! a couple of reputable automotive quotes.....

Thermostats between 180 and 195 degrees
Most thermostats are rated to begin opening between 180 and 195 degrees and will reach the full open position around 20 degrees higher, allowing coolant to flow between the radiator and engine.

With a 195 degree thermostat that means it should open at 195 degrees, thus letting the coolant flow freely once it reaches that temperature. What that will mean is that your temperatures will typically rest between 200-220 (usually around 210 most of the time) on the temp gauge.
 
All this discussion (forever) on normal XJ temp has interested me. When I bought my XJ the PO had a bad water pump so about a year before I bought it he replaced the water pump, installed a new radiator, a 195 degree thermostat, and a new clutch fan. He said it always ran hot until changing the above parts. 3 plus years later after buying it I have never seen it go higher than 210 and most of the time it sits just past 195. Doesn't matter what the outside temp is, if the AC is on, if I'm towing my utility trailer, etc. I have verified the temp using an obdII reader and my neighbor's gun. My neighbor is plumber and has it calbrated for work on water heaters and hydronic radiant floor heating. Maybe I'm just lucky. I personally believe a quality radiator and clutch fan do wonders.
 
All this discussion (forever) on normal XJ temp has interested me. When I bought my XJ the PO had a bad water pump so about a year before I bought it he replaced the water pump, installed a new radiator, a 195 degree thermostat, and a new clutch fan. He said it always ran hot until changing the above parts. 3 plus years later after buying it I have never seen it go higher than 210 and most of the time it sits just past 195. Doesn't matter what the outside temp is, if the AC is on, if I'm towing my utility trailer, etc. I have verified the temp using an obdII reader and my neighbor's gun. My neighbor is plumber and has it calbrated for work on water heaters and hydronic radiant floor heating. Maybe I'm just lucky. I personally believe a quality radiator and clutch fan do wonders.

Properly maintained, clean cooling systems work just fine on stock xjs in pretty much all conditions. If it overheats, something is wrong. It's usually a bad fan clutch or a clogged radiator.
 
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