Checking temps

I want to make sure my engine and transmission are running at the appropriate temps without hot spots. I have one of those laser thermometers which are actually quite accurate. I am planning on driving the jeep around for a while. maybe 20 mins to make sure its nice and warm and then park in the driveway and while its running just check the temps in various places on the engine and transmission. Anyone done this before?
Also what temp does the transmission typically operate at? its a 98 xj with the 4.0

Yeah i bought the same XJ a few months ago and it started over heating just yesterday lol But im curious what the appropriate temps are too.

The only useful engine temperature check is at the thermostat housing. You should see about 190° - 210° on your IR laser gun. If the routine preventative maintenance and fluid changes are all up to date, everything else will be running at the appropriate temperatures. The temp sensors themselves can be ohms tested using the chart below.



If the engine is overheating, the cooling system needs servicing.




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1991 + 4.0 COOLANT TEMPERATURE SENSOR: Temperature-to-Resistance Values (Approximate)

176 degrees farenheit has a spec between 1,170 ohms and 1,340 ohms
194 degrees farenheit has a spec between 860 ohms and 970 ohms
212 degrees farenheit has a spec between 640 ohms and 720 ohms
230 degrees farenheit has a spec between 480 ohms and 540 ohms

Thanks for the tip. My Jeep is all up to date on its fluids. I just built it in the summer of 2016. Everything including engine is new. I just want to make sure it is running at the temp the gauge claims

Using an infrared thermometer, with a laser pointer, I find the hottest spot on the thermostat housing and then paint a black dot on it, to be used as a target.
It took trying three different temperature senders to find one that agreed with an calibrated infrared thermometer.
Neither a new Standard or Mopar sendor was accurate, finally bought an accurate sendor from Napa.

The transmission's temp can be checked by getting on your knees and aiming the thermometer at the transmission's oil pan.
The trans temp can be all over the place, depending on the ambient air temp and how big a load is on the drivetrain. An outboard oil cooler will also change the temp.
I see a spread of temps from 150 to 235, the higher temps while climbing when in low range.

lazyxj said:

Using an infrared thermometer, with a laser pointer, I find the hottest spot on the thermostat housing and then paint a black dot on it, to be used as a target.
It took trying three different temperature senders to find one that agreed with an calibrated infrared thermometer.
Neither a new Standard or Mopar sendor was accurate, finally bought an accurate sendor from Napa.

The transmission's temp can be checked by getting on your knees and aiming the thermometer at the transmission's oil pan.
The trans temp can be all over the place, depending on the ambient air temp and how big a load is on the drivetrain. An outboard oil cooler will also change the temp.
I see a spread of temps from 150 to 235, the higher temps while climbing when in low range.

Click to expand...

Thanks for this. My temps were all good. No hot spots on the head or a transmission running hot. I did this because I have had 2 heads blow since 2016 and I wanted to make sure they were just due to the machine shop I used being lazy and not my mistake

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