1996 XJ temp readings at thermo housing

Hello everyone it's my first time on the forum so I hope I posted on the correct section. So I've been dealing with this issue, and maybe one of you can help me out. I've replaced most if not all my cooling system except for the water pump. I've upgraded to dual electric fans and am getting odd readings at my temp gauge. More specifically I'm overheating according to my temp gauge. I don't feel like I'm overheating. I've gone all the way into the red area with no smoking, no misfire, no boil over, no nothing. I purchased an IR gun and took readings at the thermostat housing. When my gauge reads 210 my housing reads 170. When my gauge reads 235ish my housing reads 204 max temp I was able to get was 210 at the housing. I've tried getting a reading at the temp switch, but it's nearly impossible to get an accurate reading there plus the brass fitting throws the IR gun off a lot from what I've researched online. I know I can go out and buy a gauge or aftermarket temp gauge, but has anyone had similar numbers with the IR gun? Or maybe someone can give me a baseline? I've also taken temps of the upper and lower hoses when gauge reads 235ish and both hoses temps are less than 170. Any help would be greatly appreciated.

You'll probably get a better reading on the radiator side tank near the inlet. And with the airbox out, on the end tank near the outlet. Black seems to be a better color for good IR thermometer readings. I don't know what to tell you about your hoses, It never crossed my mind to try a temp reading there..

Electromagnetic fields can mess with your thermometer, best results would be with the engine off and no rotating parts.

Put a catch pan under your XJ, take the radiator cap off (motor cold) and let it run until it heats up. Use a for real thermometer in the coolant in the filler neck. compare it to what you get with your IR thermometer. Don't rev the motor or coolant will really spew out the open filler neck, it may surge a little anyway and you will have some coolant come out (catch most of it with rags). If you take the radiator cap off when the motor is hot, coolant is going to spew all over the place, hot enough to blister your hands. Coolant and electrical don't do well together, avoid getting coolant into anything electrical (alternators, motors, connectors or whatever).

When you are done, rinse off the area near and under the filler neck with water and flush it into a catch pan. You really shouldn't loose more than a pint of coolant, likely less.

I too have a 96 and get readings much like yourself.With an aftermarket temp guage and sender(Autometer) readings at the rear of the head will be 15* hotter than what the sensor at the T-stat housing sees, this has been checked with a Snap-on Scan tool and with a Actron scan tool.
Temp gauge runs steady at 210,,,,,under a long hard pull up a grade the temp will see 230+,but it has never puked any coolant or shown any other signs of really overheating,

This motor has now passed 374,000 miles and has never had the valve cover off in the time I have owned it(since 40,000).
Don,t fret over it,210 is normal ,230- be aware and take care,,

So Wayne your getting these temp readings with a gauge not with an IR gun correct? And you are getting confirmation of your Autometer readings through a scan tool? See my temps seem high for not really doing anything, but driving. I'm not pulling a boat or going uphill my temps just creep. Granted it's hot out and I have the a/c blowing, but 235+ with no overheating symptoms i.e. steam, coolant boil, etc. seems weird to me. I was also able to point my IR thermo to the back of the head from the front of my vehicle at the temp switch and it had the same temp as the front thermo housing 204 when gauge showed 235. Maybe I'll go down to my local shop and have it scanned.

Yes ,readings are from the guage,,,I do have an IR gun,just never used it.
Scan tools both showed a 15* difference from T-stat housing sensor to guage sender at back of head,scan tool gets no reading from autometer guage sender.Dedicated wire to gauge.

Later models have only one sensor...ECU tells the guage what to read. Ours and earlier have sensor in stat housing for the ECU and sender in back of head for the dash guage......both see different temps..

Jeep gauges are often way off. Either the dash gauge is way off, the sensor in the rear of the head is off (bad) or there is a ground or wire connection issue. Trust the IR!!!!

Wayne would you mind taking some IR readings for me? I took some IR readings when my gauge said 210 on initial startup and want to match my results. Could you maybe take the readings when you first start your Jeep and warm it up? When the gauge reads 210 let me know what your IR readings are at the housing and at the rear head area near the switch. If you could so that it would really help me out. I mean I would like some extra piece of mind.
Ecomike

I tried to space out my reply and it submitted. Anyways Ecomike thanks for your advice. I trust the IR readings more than the gauge, but I am one of those obsessive individuals that likes multiple second opinions i.e. scan gauge etc. Thanks!

Ham1996 said:

I tried to space out my reply and it submitted. Anyways Ecomike thanks for your advice. I trust the IR readings more than the gauge, but I am one of those obsessive individuals that likes multiple second opinions i.e. scan gauge etc. Thanks!

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I have a Scan Gauge that plugs into the diagnostic port. It get its readings from the PCM thus it could only report what the PCM sees i.e. if the sender in the front of the head is bad, the PCM and Scan gauge will both repot bad readings. If I have doubts about the temperature, I put a 'T' in the out let to the radiator and use a mechanical temperature gauge to confirm. I then reference that reading in future dash readings. After the 4.0L is properly warmed up, all readings on my XJ are usually within 5* of each other.

I am yet to use an IR gun to get water temperature. The reason being 1) you need a clean area to aim the laser beam at. 2) The external temperature will be cooler than the actural water temperature.

I have an 87 with a temp huge plugged into the newer style t-stat housing. The stock temp reading from the back of the head on mine will be 210 when the Tstat reading settles about 195. I had though that my gauge was just off that much. But there are times, like on long grade in HOT weather with the AC on that the tstat reading will rise to 220-230ish and the stock reading will be about the same. When it cools back it will revert to the 195/210.

on long downhill COLD stretches the tstat reading will stay around 190 and the stock back of the head reading will drop to around 190.

It seems on mine that the back of the head is the hottest part of the engine.

Ham1996 said:

Wayne would you mind taking some IR readings for me? I took some IR readings when my gauge said 210 on initial startup and want to match my results. Could you maybe take the readings when you first start your Jeep and warm it up? When the gauge reads 210 let me know what your IR readings are at the housing and at the rear head area near the switch. If you could so that it would really help me out. I mean I would like some extra piece of mind.
Ecomike

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IR gun went "walkabout" have to check with my son.If found I will report in a couple days.

Hello everyone thanks for your replies. Techno1154 I know exactly what you mean. However my CTS is new and I tested it using a MM and water on the stove. According to the FSM it's within spec. I took some more readings today after I got off of school and my readings are pretty close to each other. I took readings from the thermo housing and head near the switch. While my temp gauge was reading 235ish my IR gun had temps no where near 210 at those locations. More like 204 at the housing and 200ish at the head. Way under 210, but I attribute those temps to my dual fan setup. Wayne I hope you find your IR gun. Let me know your temps when you find it. I've also called some shops in my area and had no luck with the scanner tool some say its broken and others give me other excuses. Yes I live in a crappy little city. I'll keep you guys posted when I get the scanner readings. Again thanks for the help and replies.

Found IR gun,,,,It was in case with scan tool,,,,Doh,,logical place for it to be,,,
Scan tools are relativity cheap.E-Bay had Snap-on "Brick" scanners for cheap,as they are about 3 generations behind what it used in the repair world today....they still give real time info displays,which is all we need.

Yeah I saw one online for 50 bucks I cant remember the name but it had good reviews. Had real time info i.e. air fuel, water temps etc. Maybe I'll pick one up. So shoot me those IR numbers when you get a chance. Thanks!

Ok ,here are the reading I took today..
Am,,3 mile drive, raining,100% humidity,,Tstat housing-186*,Rear of head on sender area-197*,bottom of radiator at hose outlet-133*
PM,,11 mile drive,Not raining,99% humidity,,, 185*,200* and 129*

Temp guage reading about 210* at all times,engine running at both times

As said, use a obd2 scanner and compare what the pcm sees the cts to be and what the IR reading is at the t-stat housing by the cts sensor. That oughta give you a good idea how accurate the IR readings are. The rear temp sender will be hotter than the front cts.

Well that pretty much confirms my suspicions. I have similar readings + or - some degrees, but my gauge doesn't reflect 210. My gauge always runs hot even if my readings are not. I will still verify with a scan tool. Will replace the switch on the back of the head and report back to you guys. Wayne I appreciate your help, I really do. I also want to thank everyone else for contributing. Thank You!!

Same issue here
My gauge on my dash reads 20-30 degrees hotter than the mechanical gauge I installed on my thermostat housing.