Does your temp gauge hang out in this range?

S

SuperRA

NAXJA Forum User
Location
Santa Clara, CA
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It fluctuates from just below the white line on the left of the needle to just under the red area.

The gauge sensor is new and I checked it's resistance at ~100*F and it's on spec. A thermocouple placed on the thermostat housing inbetween the hose and housing reads from 90-95C (194-203F). Just wondering if this is the normal position for the needle?
 
my 92 xj dd same thing. threw parts at it, but it needed a MOPAR brand sending unit. I had replace the sender twice with BWD, but they were both bad, despite OHM tests being ok. Get MOPAR on this particular part.
 
The guage can also become out of alignment, as its calibrated with a glued on magnet.
Have you tried checking resistance when hot to verify that the correct info is being.sent?
 
scot4free said:
my 92 xj dd same thing. threw parts at it, but it needed a MOPAR brand sending unit. I had replace the sender twice with BWD, but they were both bad, despite OHM tests being ok. Get MOPAR on this particular part.
Click to expand...

I'll check that out. If my autozone sensor doesn't check out, that'll be the first thing I do.

souske said:
The guage can also become out of alignment, as its calibrated with a glued on magnet.
Have you tried checking resistance when hot to verify that the correct info is being.sent?
Click to expand...

That's the thing, how to I get the correct info? Is the thermocouple on the outside of the housing accurate enough? I would think that it couldn't be too far off as aluminum should conduct heat rather well. I checked the resistance of the sensor, but I didn't have a chart with the resistance I was at.
From the wiring diagram it should be: 100F = 1600ohms, 180F = 309ohms & 240F = 113ohms.
I guess I'll be doing some excel-ing. Hopefully the sensor is linear.

EDIT: the sensor is not linear according to these numbers.. The best fitting trendline is a "power" with the equation y=3E+09x^-3.138 I don't know if that is correct or not. I guess it would be easier to boil the sensor on the stove and verify the 180F number. I won't be able to reach 240F.
 
Last edited:
Since yours will be pulled out to boil it, replace it....trust me... water pump, radiator, flush, checked head gasket by several methods...watched hours of youtube videos on head replacement... all due to a sender that was not from MOPAR....I wasted hundreds of dollars and hours of my life due to a sensor that OHM'd great, but alas, was Autozone/O'Reilly's.
 
SuperRA said:
I'll check that out. If my autozone sensor doesn't check out, that'll be the first thing I do.



That's the thing, how to I get the correct info? Is the thermocouple on the outside of the housing accurate enough? I would think that it couldn't be too far off as aluminum should conduct heat rather well. I checked the resistance of the sensor, but I didn't have a chart with the resistance I was at.
From the wiring diagram it should be: 100F = 1600ohms, 180F = 309ohms & 240F = 113ohms.
I guess I'll be doing some excel-ing. Hopefully the sensor is linear.

EDIT: the sensor is not linear according to these numbers.. The best fitting trendline is a "power" with the equation y=3E+09x^-3.138 I don't know if that is correct or not. I guess it would be easier to boil the sensor on the stove and verify the 180F number. I won't be able to reach 240F.
Click to expand...

I'm old school and use a surface digital thermometer. I bought a tube of conductive heat paste at an electronics store years ago (a little goes a long ways). I tried using an IR thermometer and got around 50% erroneous readings, it seems to do better on black parts and away from moving parts. I noticed the moving fan blade tended to screw with it, why exactly I don't know. Comparing my surface temp. at the thermostat housing I compare to the gauge readout and then extrapolate. A good indicator of accuracy of the gauge is when the aux fan comes on.

Lightly sanding a spot on the thermostat housing to remove oxidation, heat conductive paste and a little pressure will get you a fairly true reading.
 
scot4free said:
Since yours will be pulled out to boil it, replace it....trust me... water pump, radiator, flush, checked head gasket by several methods...watched hours of youtube videos on head replacement... all due to a sender that was not from MOPAR....I wasted hundreds of dollars and hours of my life due to a sensor that OHM'd great, but alas, was Autozone/O'Reilly's.
Click to expand...

To me this doesn't make sense. You haven't explained why the Mopar sensor worked and the other one did not.. All the gauge cares about IS the OHMS.. That's all it "sees".

Well, in any case, I know everything else is ok. Much if not all of it has been replaced during the rebuild. I'm fairly confident of the thermocouple readings as well as the electric fan sensor doing it's job cycling the fans. It turns on low at 198F and high at 205F and the fans never turned onto high. It's gotta be either the sensor or the gauge. You may be correct in saying that it's the sensor, but it would have to be out of spec to be so. If it's correct to spec, I don't care where it's from, it should still work.

I haven't checked the grounds yet, i.e. resistance from sensor to the negative terminal, but the way that the sensor works, if there was bad grounds (more resistance) then the gauge would read lower than actual temperature.
 
For some reason, when it comes to sensors and sending units, XJ's don't seem to like a lot of the after market parts. The Mopar units cost a bit more but if your time is worth anything, it is probably cheaper to use the Mopar once than to replace an after market unit two or three times.
 
The sensor is not "seeing" ohms, but creating them based in electrical resistance, which is changing with heat increase or decrease. That's the problem. When made poorly, the "scale" is way off. Not sure why to be honest, but changing my gauge sending unit was like magic...I had struggled for months not driving more that 5 miles at a time.
 
scot4free said:
The sensor is not "seeing" ohms, but creating them based in electrical resistance, which is changing with heat increase or decrease. That's the problem. When made poorly, the "scale" is way off. Not sure why to be honest, but changing my gauge sending unit was like magic...I had struggled for months not driving more that 5 miles at a time.
Click to expand...

I said the gauge "sees" the ohms not the sensor. I agree with your explanation of the sensor. Electrical resistance IS ohms... When you said "Ohm test" I take that to mean that the correct resistance is measured for a given temperature at many data points throughout the range. So your aftermarket sensor did in fact NOT pass the ohm test, otherwise it should work.

Anyhow, it's either the gage or the sensor, and if it is the sensor, I have no problem switching it out for a MOPAR unit. In fact, I hope it's the sensor! That's quite a bit easier to do...
 
Mine gets to just below that line and then I turn off A/C and if it gets to the line I turn on the heater. When I turn the heater on it drops down to just over the 210 mark in a few minutes.
My Jeep is new to me but the PO told me he had replaced the radiator less than a year ago and it looks new so I don't doubt it. I replaced the tstat and housing since it had a weep. Good thing I did, because when I took it off I was scraping the scale off and a big hole opened up.
I'd like to get the temps down some too, as it is now I'm afraid to take it too far on the highway and driving around AZ in the summer sucks without AC.

Is there a good write up on how to test the sensor? I have an okay multimeter but only used it for basic stuff.
 
i have a mechanical gauge installed in an adapter in the heater hose from the t-stat housing.

My dash temp gauge shows where yours is when the water temp is @ 210* per the mechanical, no matter what sending unit I have put in there.

The dash gauge is bad.
 
That shows about 230 deg., but probably incorrect like others have said. I have the DBO triple fan kit, with the inline fan controller. Have also checked with a heat gun. My gauge is at least 10 deg over what it should read. Knowing for sure is key.
 
Re: Re: Does your temp gauge hang out in this range?

Special K said:
How much affect should ambient temps have on the cooling abilities?
Click to expand...

Mostly depends on how well your system is working.
 
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