Thanks guys, I will report back to let everyone know if and when I find the problem...

Well I have a oe radiator and 190 t stat mine stays at 190 hwy and 215 to 218 in town and on the trail Ans I have the factor electric fan and the Zj clutch fan and I'm in Arkansas were the humidity is horrible lol just giving my 2 cents I've heard anything under a 190 just hurts the poor 4.0 cause they run so hot anyway I also have Hood vents and lifted Hood for more circulation.hope you get it figured out

OK, I have changed my upper and lower radiator lines, heater valve, water pump, spark plugs and did a compression test (135-140 all cylinders). I flushed the entire system in any orfice I could fit the hose in and run water through. Tried two different radiator caps, radiator is a new 3 row, took the heater core out of the system, this thing is still wanting to run hot. I have burped the system, tested the t-stat in a pot of water and it opens at 162-164 degrees on a 160 stat.

I do not know where to go next. Idles at 160-170, but rev it in the driveway and the temp starts to climp, drive it down the street and the temp starts to climb...I am dumb founded, it is a simply system so why can I not find the problem???????

probably have a clog... flush it both ways with the thermostat and possibly water pump if you feel like it.. but probably gunked up somewhere

I did that once I installed all the items listed above today, still came out clear and free from debris. If it was clogged somewhere it should have came out by now as many times as I have flushed it, I would have thought anyhow!!

Seems odd it would run cool idling but temp rises when revving/driving.....have u verified temps with a temp gun? Anything blocking the grille, big tires? A head scratcher.

I have a winch and some lights up front but nothing has been added recently. I watch the temp go up and jump out and hit it with the temp gun to confirm the temp...It's right where the gauge says it is...

My next thing is to check the cat for blockage and replace if needed, and also clean my A/C condenser, it looks good but some places are "Questionable". I would think if it was clogged or blocked enough though it would run hotter at idle as well???

DUMBFOUNDED I AM I TELL YA!!!!

Any way to turn the fans off? Seems like I read somewhere that a running efan, at hi-way speed, could actually impede air flow thru the rad thus reducing cooling efficiency. I think on most computer controlled vehicles, the vehicle speed sensor will kill the efan(s) once X vehicle speed is reached so as to not impede air flow . Again, may be worth a try.

Ever figure this out?

Im having the EXACT same prob in my new XJ. Has a 3 row all alum rad, new t-stat, new water pump, new hoses, no coolant in oil or coming out the tail pipe.

I am running dual elec fans, but it did it with the mechanical fan too.

I have been having the same problem for months. I have replaced everything in the cooling system and even put in an Autometer gauge. I have decided to drive it until it blows then replace the motor. If you figure it out please let me know.

Maybe it is running too lean. Map sensor output range is (middle wire) between 1.5 volts dc and 2.2 volts dc. 1.5 volts is the leanest and 2.2 volts dc is the richest. A lean condition will cause more heat during combustion.

check for intake vaccum leak. intake/exhaust manifold bolts loosen over time on 4.0 liter inline 6 motors. causes a lean condition which leads to over heating and poor power, and erratic idle, hesitation when accelerating etc....

the computer will richen the air fuel ratio (choke on) when the temp is below 160 and will remain in closed loop mode (no sensor data is used), open mode uses sensor data to regulate fuel air mixture. If the engine stays below 160 degrees you mpg will suck.

Just pointing out this thread is from 2012!!