Jeep Runs Cool....Need infrared temps confirmed

Hi, new here but lurking for over a year. Have some questions about my 4.0HO.

The Jeep for reference:
96 XJ 4.0 HO auto
3" lift BDS with 31.5x15 BFG AT
K&N Cone Filter
Flowmaster rear exhaust with mid muffler removed

Brand New (MOPAR only parts): Waterpump, radiator, hoses, thermostat (well, 4th one), coolant flush (ethylene glycol)

She runs great, but she was running at 160. Replaced tge thermo for the 4th time and shes now running better, but she still sits under 210 (or so says the guage), im guessing around 170-180. Im getting 15mpg straight highway, bout 200-220 a tank. Broke out the infrared.

Thermostat housing is 210 on the nose (fluxing from 190-212).
My rear sensor on the head (controls the guage) only reads around 150-170 (pointing at the brass fitting). Is it the sensor, or is my coolant not warm back there?

Should the blocks temps be pinging 210 as well? And what should the temp of the upper hose be ? Stumped why i cant get her to run at 210.

Help please

sounds like you have an air bubble at the back of the head keeping the gauge from reading right, the sensor at the back only runs the gauge, the one at the front tells the computer what to do (and 190-212 is exactly where it should be.) have you tried replacing that sensor?

Don't poke the bear...It runs cool, unlike most people's complaints of can't keep it under control.... be happy unless you are not getting good heat ion the cab.

Digger87xj said:

Don't poke the bear...It runs cool, unlike most people's complaints of can't keep it under control.... be happy unless you are not getting good heat ion the cab.

Click to expand...

Never replaced the rear sensor as its a bitch to get to. She was overheating, hence the new cooling components.

Any particular way you guys burp air? I thought i got it all out. Any other suggestions?

Anyonw with the upper hose temps?

Anybody possibly with an infrared and rear sensor tell me what yours reads at on the sensor?

Bubbles usually cause hot spots and flow problems, which you are not experiencing.

I can't give you a reading.. I don't have a 4.0.... it's a 5.9 in mine.

Anyhow, I wouldn't be troubled by it, though it's not a bad idea to change the rear sensor. Might as well go OEM on that one too, just to keep aftermarket variances to a minimum.

Digger87xj said:

Don't poke the bear...It runs cool, unlike most people's complaints of can't keep it under control.... be happy unless you are not getting good heat ion the cab.

Click to expand...

I agree. Mine runs cool NOW...it was running hot. I spent all summer messing with it until I finally got it under control...now it's cool as I said, probably a stuck open t-stat. I'm just going with it for now, heater works fine, mileage good. Nuff' said.

With the engine COLD, have your XJ at a slight incline so the engine sits at a backwards angle. Remove the rear sensor and let fluid run out of that sensor hole and then reinstall the sensor. Another thing you can do, that my self and some others do. Drill 2 holes in your t-stat at the "6 and 12 o'clock" positions. This allows some coolant flow through the system at all times, even if your t-stat sticks closed.

'91+ open cooling systems self-burp without holes in the thermostat, being on an incline etc.