• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Erroneous temp readings?

O

Oatmeal

NAXJA Forum User
Location
Cedar City, UT
Lately my '96 has been running pretty hot....or has it?

So far I've had my 3 row CSF radiator rodded out, new water pump, Robert Shaw high flow 195* stat....even replaced my cat since it was original and partialy (but not too bad) restricted.....my fan clutch is fairly new.
All of this things haven't made one bit of improvement.

Checking temps with my IR thermometer I get about 209*-212* at the water outlet hose (right where it connects to the outlet) when the gauge is creeping towards the white line before the red (240*?)

The fan kicks on at about halfway between the 210* mark and said white line and off again just before dropping back down to the 210* mark.

Here's the thing my Jeep never used to get anywhere near that hot, even with the AC on pulling a steep grade in the summer heat (like now) it would barely get above 210*...oh it does have a good trans cooler and 4.88 gears on 33s so it's not being overworked.

Now here's the big question, I had replaced the gauge sender with a parts store unit (NAPA) and am wondering if maybe I'm getting false readings at the gauge...opinions?

I'm reluctant to buy a dealer part at $40+ if those numbers are where they should be.

Stumped!

Thanks,

Hans
 
Sounds to me like you have a bad temp gauge, bad wiring, bad sensor or a combination of the above. MY money is on a bad sensor or bad wiring connections, ground, or sensor contact, or sensor ground to the head it is threaded into.

I have about 5 new temp sensors from various sources and none of them work right (And even tested one of them to OEM spec with an ohm meter, and it was good!!!), and I finally gave up getting my dash gauge to read right anymore.

Trust the IR readings under the hood, and then use an offset on the dash gauge, that is what I finally did. On mine 120 on the dash gauge is 200 F, LOL!!!

Most of the temps you posted fail to say which gauge gave that temp!!!! So please repost all the readings based on the gauge used, dash versus IR.
 
my IR is showing 155-170 when the gauge is showing 215. something aint right! been fighting overheating for a couple weeks, turns out it's the stupid gauge.
 
Ecomike said:
Most of the temps you posted fail to say which gauge gave that temp!!!! So please repost all the readings based on the gauge used, dash versus IR.
Click to expand...

Oatmeal said:
Checking temps with my IR thermometer I get about 209*-212* at the water outlet hose (right where it connects to the outlet) when the gauge is creeping towards the white line before the red (240*?)
Click to expand...
This one's pretty obvious

Oatmeal said:
The fan kicks on at about halfway between the 210* mark and said white line and off again just before dropping back down to the 210* mark.
Click to expand...
As indicated on the dash gauge



Just ordered a factory sender from the dealer.....it was $29 not $40 but, still a lot of money for such a small part!

Hans
 
Vanimal said:
my IR is showing 155-170 when the gauge is showing 215. something aint right! been fighting overheating for a couple weeks, turns out it's the stupid gauge.
Click to expand...
The part that sucks the most.....driving back from Utah, through the desert with the AC off and the heater on, thinking I was on the verge of overheating.

Damn, I could have been cool!

Hans
 
I had problems with two different NAPA senders. Both read about 20 degrees high. Pick up one by Standard, think it was a TS199...gauge is a lot more accurate now.
 
#S194 said:
I had problems with two different NAPA senders. Both read about 20 degrees high. Pick up one by Standard, think it was a TS199...gauge is a lot more accurate now.
Click to expand...
Where were you before I ordered the dealer part?

JK, thanks for the tip....good to know should it pop up again.

Hans
 
Also, make sure and get any air bubbles out of the system.
 
I thought mine was high, running 210 on dash gauge, so I popped in one of those thermometer radiator caps and it was 190!!

Sounds like my new temp sender is not so great either. I know my e fan won't run until I have 215 indicated on the dash, is that the set point?
 
same odd issue here. thinking my rig is running hot. But rad is new 3 core csf, burped air, good tranny cooler, flushed system, and a new sending unit (renix, 89) from rockauto , and thats when it started running too hot. anyone using an aftermarket gauge? if so , where do you actually hook it up to on the engine?
 
X E Ryder said:
I thought mine was high, running 210 on dash gauge, so I popped in one of those thermometer radiator caps and it was 190!!

Sounds like my new temp sender is not so great either. I know my e fan won't run until I have 215 indicated on the dash, is that the set point?
Click to expand...

That doesn't mean your sender isn't working; it means your radiator is.

Yes, the efan should be coming on at about 218*, give or take a few degrees.
 
Well, put the OEM sender in and all seems good now.

Took on the hill that had it creeping towards the red before (AC on)....now it stays at just a tick past 210* (it was hot today).

Stays at or just below 210* driving in town with AC full blast...what a relief.

I pointed my IR temp gun at the sender itself and it reads slightly cooler than the dash gauge itself.....finally some peace of mind.

Thanks all,

Hans
 
X E Ryder said:
I thought mine was high, running 210 on dash gauge, so I popped in one of those thermometer radiator caps and it was 190!!

Sounds like my new temp sender is not so great either. I know my e fan won't run until I have 215 indicated on the dash, is that the set point?
Click to expand...

Take into account that if you're measuring coolant temp at the radiator cap, the coolant has already flowed through the radiator and heat has been removed so, your gauge is probably pretty close.

Hans
 
X E Ryder said:
I thought mine was high, running 210 on dash gauge, so I popped in one of those thermometer radiator caps and it was 190!!

Sounds like my new temp sender is not so great either. I know my e fan won't run until I have 215 indicated on the dash, is that the set point?
Click to expand...

About 212 at the T-stat temp sensor seems to be the E-Fan cut on temp for a lot of OBD-II vehicles, so yes.

The older the radiator, the slower the flow through the radiator, the larger the temp drop from the t-Stat sensor (or block temp sensor) to the Radiator cap sensor. Mine was about 40 F Delta T, then it was only 10 F delta T with the new 3 row radiator (due to faster flow!!!!!).
 
hey hans,
glad your issue is resolved.
heres something for everybody else to keep in mind...
customer brought in a 93 cherokee country with 78000 miles. customer complaint of overheating. previously took to another local shop. replaced faulty clutch fan, didnt fix problem. then replaced radiator, didnt fix problem. at this point customer was upset that she had spent money that didnt fix problem.
when vehicle came to my shop i verified overheat condition. gauge showed 240*-260* e-fan on
checked coolant temp reading with scanner... 220*-230*
checked coolant temp at coolant temp sensor, 220*-230*
checked coolant temp at gauge sending unit (rear of head) 240*-260*
i then proceeded to remove thermostat... once housing was removed i found the thermostat had come apart.
i removed the thermostat and broken pieces then replaced it with a regular stant 195*
filled and bled cooling system. test drove and all readings were back to normal. vehicle never got over 210-215*
this all happened last week. im down in garden grove and it was kinda hot last week too.
hope this helps somebody :cheers:
 
took the IR gun to my junk today. also was trying to burp system more, jacked up rear of vehicle real high, and popped out the temp sensor at the back of the block. after that , popped the rad cap off (converted to open system) with heater on for a while, then let it run with a/c cranking to get it up past the 210* mark on the gauge.

180* tstat, new 3 core rad, newer efan (98+)
here are some readings

(my efan is wired to a switch, doesnt come on until i turn it on)

measurements round 1 :
No efan, just left it idling for a long time until it got to 215+( basically the gauag was around 215-22- id guess) maybe idled for 30-40 minutes+ :

sending unit at the back of the block: 270* (that seems really hot?)

radiator from the front by the lower radiator hose : 175*
tstat housing : 210*
hose right after t stat : 190* (20* difference between t stat housing and the hose 2 inches past the housing?weird...)

rad cap area(no cap on at the moment) : 175*
upper hose at inlet into radiator : 175*

measurements round 2:
no cap on, turned jeep off, measured right after the above measurements, basically at this point it had probably idled an hour?) jeep gauge temp crept up a hair, stayed around the 215-220* range :

sending unit at the back of the block: 230*
radiator from the front by the lower radiator hose : 189*
tstat housing : 213*
hose right after t stat : 180* (33* difference between t stat housing and the hose 2 inches past the housing?weird...)

rad cap area(no cap on at the moment) : 155*
upper hose at inlet into radiator : 192*

measurements round 3:
after all of the above, i installed 16lb cap(brand new) , turned on jeep, turned on efan, , measured right after the above measurements( directly after round 2)

sending unit at the back of the block: 250*
radiator from the front by the lower radiator hose : 160*
tstat housing : 195*
hose right after t stat : 180* (33* difference between t stat housing and the hose 2 inches past the housing?weird...)

rad cap area(now it has a cap on ) : 135*
upper hose at inlet into radiator : 154*


my question is , what is the right temp?

the sending unit area at the back of the block gets insanely hot, while the rest of the rig seems to stay pretty cool, and once i put a 16lb cap on and cranked the efan the gauge temps dropped from 215 down to under 210.
 
radiator from the front by the lower radiator hose : 175*
tstat housing : 210*
hose right after t stat : 190* (20* difference between t stat housing and the hose 2 inches past the housing?weird...)
Click to expand...

That is normal. The hose is an insulator, and the heat transfers through the rubber too slow, and the exterior hose cools from the ambient air flow to a low temp, the metal T-stat housing is is a heat conductor, or it is much close to the actual coolant temp inside the T-Stat housing.
 
blondejoncherokee said:
took the IR gun to my junk today. also was trying to burp system more, jacked up rear of vehicle real high, and popped out the temp sensor at the back of the block. after that , popped the rad cap off (converted to open system) with heater on for a while, then let it run with a/c cranking to get it up past the 210* mark on the gauge.

180* tstat, new 3 core rad, newer efan (98+)
here are some readings

(my efan is wired to a switch, doesnt come on until i turn it on)

measurements round 1 :
No efan, just left it idling for a long time until it got to 215+( basically the gauag was around 215-22- id guess) maybe idled for 30-40 minutes+ :

sending unit at the back of the block: 270* (that seems really hot?)

radiator from the front by the lower radiator hose : 175*
tstat housing : 210*
hose right after t stat : 190* (20* difference between t stat housing and the hose 2 inches past the housing?weird...)

rad cap area(no cap on at the moment) : 175*
upper hose at inlet into radiator : 175*

measurements round 2:
no cap on, turned jeep off, measured right after the above measurements, basically at this point it had probably idled an hour?) jeep gauge temp crept up a hair, stayed around the 215-220* range :

sending unit at the back of the block: 230*
radiator from the front by the lower radiator hose : 189*
tstat housing : 213*
hose right after t stat : 180* (33* difference between t stat housing and the hose 2 inches past the housing?weird...)

rad cap area(no cap on at the moment) : 155*
upper hose at inlet into radiator : 192*

measurements round 3:
after all of the above, i installed 16lb cap(brand new) , turned on jeep, turned on efan, , measured right after the above measurements( directly after round 2)

sending unit at the back of the block: 250*
radiator from the front by the lower radiator hose : 160*
tstat housing : 195*
hose right after t stat : 180* (33* difference between t stat housing and the hose 2 inches past the housing?weird...)

rad cap area(now it has a cap on ) : 135*
upper hose at inlet into radiator : 154*


my question is , what is the right temp?

the sending unit area at the back of the block gets insanely hot, while the rest of the rig seems to stay pretty cool, and once i put a 16lb cap on and cranked the efan the gauge temps dropped from 215 down to under 210.
Click to expand...

The IR gauge looks at an area, that grows as R squared as your tester gets farther away from the test surface. That rear sensor is only about 3/8" to 1/2" from the rear #6 exhaust port-manifold (which is at about 600 F), and you may be reading some it, and the head right at it, in which case you are OK. The rear sensor IR temp is the only one you posted that looks like a possible concern, and it may simply be measurement error. A slight change in angle and distance of the IR tester taking that measurement can cause an easy 50 F swing in the reading at that spot!!!!

http://www.q3i.com/allaboutinfraredthermometers.php

Distance from the object you're testing (D:S Ratio) ​
Typically the lower cost models have lower D:S ratios such as 4:1 or 6:1. As you get into higher quality models you see higher ratings such as 12:1 or even as high as 60:1. So what is the D:S ratio anyway? The sensor of an infrared meter picks up its radiation readings in a defined circular spot. The target must fill this spot or you will be measuring emitted infrared radiation from the area outside of the target which will cause an inaccurate reading. The D:S ratio is defined as the relationship between the distance of the measuring device from the target and the diameter of the testing spot. The higher the rating, then the smaller the spot you can measure from a set distance. For example, you have a I.R. thermometer with a 4:1 D:S ratio, then you can measure a target with a diameter no smaller than 40mm from a distance no farther than 160mm. If your I.R. thermometer had a D:S ratio of 12:1, then you could measure a spot with a diameter as small as 13mm from a distance of 160mm. Think of the D:S like the magnification power of the scope on a gun. (i.e. you can accurately hit a smaller bulls-eye with a more powerful scope). If you are testing close to the object or in a small space (such as a testing circuit board for hot spots), we recommend a small maneuverable model like the ThermoHAWK™. If you are testing objects with extreme temperatures or items that are hard to reach, then a model with a high D:S ratio is a good choice.​
Click to expand...

http://www.allqa.com/IR.htm

Has a good image, picture of the D/S issue!!!
 
Last edited:
You must log in or register to reply here.

Similar threads

V
High temp woes
2
Replies
21
Views
413
Vitzaa
V
R
Fan not turning on when hot- fan works!
Replies
2
Views
2K
JMA_2001XJ
J
T
OBD2 coolant temp readings
Replies
2
Views
1K
maxbraketorque
M
U
Overheating? Quick help please.
Replies
9
Views
2K
75SV1
7
M
Oil pressure question
2
Replies
26
Views
3K
Money_Pit_Incoming
M
Back
Top