I will be as brief as possible. First I am an active technician of many years but this one has me stumped. I will attempt to be as concise as possible and not leave out any relevant info.
My '01 XJ 4.0L is running warmer than I think it should. The gauge, scanner, and infrared all agree that once it's up to running temp I'm at 215-220 give or take a degree or two. It has been warm here (ambient temp) but not anything out of the ordinary for CO this time of year.
A couple weeks ago I added a med duty (7 1/2" X 11") trans cooler in front of the condenser, left side, middle mount. After that is when I "noticed" it was a little high on the gauge, I've never had occasion to need one so I thought to myself 'Well the trans runs pretty hot, pulling heat across this cooler may reduce the radiators efficiency'. In other words, maybe this is normal...
Despite this thought, it was buggin me, so having an insider at a parts place, I installed a 3 row copper/brass HD radiator... no change.
Dropped the T-stat from 195 to 180... no change.
Installed a switch to override the aux fan for manual operation (run as long as I want it to)... no change.
It's running perfectly except for this (fuel trims, etc. etc.)
It's making me crazy fellow Jeepers!! Normal maybe? Any ideas?

Oh and on another subject, anyone have experience with hood vents for the hereditary hot soak issue with the XJ's?
I have some picked out but wonder if they are really worth the hassle.

Thanks for reading and any ideas!
K

 

In my experience, the CAFE emissions XJ's run hotter than the rest of 'em.
Think on it like this; the 0331 head was designed, as Ive read, with smaller exhaust ports for faster warm up for the CATs. That said, keep that in mind too, two small CATs right under the intake.
I constantly got heat-soaked injectors.
Also, know that 0331 heads are prone to cracking between 3 and 4. My valve-train was spotless, and I mean spotless. This would lead me to think that my head was cracked and SLOWLY losing water, otherwise it ran great comparatively to other 4.0s.
Finally galled cyl 2 when I lost a freezeplug

 

I would add a bottle of flush/cleaner and drive for a week and then flush and replace coolant with new.
I add a bottle of 'water wetter' Walmart brand which seem to help stabilize the temps.

Depending on the age of your water pump, it could be a problem. I would replace it after you use the cleaner/flush/fill. I have had good luck with Flowcooler WP and also with Parts store brand.

Might also have a bad mechanical cooling fan clutch/coupler unit. Hayden is good. There is also an upgrade unit, will have to search the part number.

Definitely hood vents work or 1" hood lift. Makes a big difference.

 

Put the correct thermostat back in. You're now forcing your engine to take longer to warm up, causing more wear and tear, and the fully warmed up running temperature will be exactly the same.

The fact that you don't see any difference in temp when you run your e-fan makes me think you have a bad temp sensor. You should see the temp drop within seconds of that coming on, relative to the temp before you turned it on, regardless of whether or not it is running hot.

If the temp drops at speed, replace your fan clutch.