I went thru the same thing here. Everything was 100% brand new in cooling. Every belt, hose, radiator, flush, pump, proper coolant, sensor, fan, clutch, 4 different stats, etc. everything. Temps were still high. I put in the grey lower temp t-stat and brought me to where I should be. I sat for an hour in 100 degree heat with the intake temps above 150 with the heat off the street going to a Yankees game, and she never went over 212.
If you did a new fan, make sure it is the right direction. I don't know how, but people said it can be done. Also, don't get the heavy duty fan clutch. It did zero for me. For the fan, take a piece of paper and make sure air is being sucked thru the grill and not pushed out. Finally, do the same with the electric fan. I've been told on here that can be reversed too.
In all though, sounds like you have the same issue I do. Look for some of my posts on it.

 

And to add on my last thought, when I put one of my new stats in it was bad from the factory and didn't open. My temps were higher on the highway then as the engine is working harder and there is no flow thru the radiator. If not the stat, was it maybe installed wrong with the wrong hose going to the output?

 

Double (and triple) checked the fan...it is definitely sucking air through the radiator. I'm going to pull the thermostat today and try a replacement. (Or more likely, I'll just drill a couple holes in it and see it that resolves the problem while I wait for a replacement to show up.)

Shouldn't be installed wrong, at this point I'll double check that too...in fact, I never really disconnected it when I replaced the radiator, I just pulled the bottom hose loose slid the wrecked rad out, the new rad in and hooked the bottom hose back up. Given that my temps were low before the fan exploding, I can't imagine that it was hooked up wrong for the past 25k miles and performing as well as it was...

 

Wires from the temp sensor to the ECU going bad?

 

I could only hope it would be so simple...

Update: So last night I combed the radiator fins that were bent (they just weren't all that messed up) and I pulled the t-stat. After cleaning the t-stat up a little I took it in the house and tested it by boiling it. I can definitely say that it isn't stuck and by the time temps get to ~195 it is completely open.

When I put everything back together I succeeded in snapping off the lovely little plastic bleeder screw, so today I picked up a couple replacements from my local BMW dealer and will take a poke at getting everything back together tonight after coaching my daughter's soccer practice.

(FWIW, I've ordered a new t-stat and a water pump in case this issue persists...if I don't need them, then they'll become trail spares.)

 

OK guys, this should be my final update. Sorry about writing a small book, but it's been a busy few days...

Last Sunday morning I got up tossed my parts and tools in the D2 and started to head over to by friend's shop. A half mile from home I realized I'd forgotten my blackberry so I had to turn around go back. (I'm on call for work 24x7.) When I came back out of the house, I noticed a faint burnt rubber smell and a little steam coming from under the hood.

It turns out that I had not secured the top shroud correctly and the fan had cut the top cooling hose. (Dumb move on my part.) Luckily I'd turned around when I did and the coolant reservoir was still more than half full. Having had issues in the past, I also happened to have a spare top hose so I quickly installed it and re-bled the cooling system.

Much to my surprise, this latest bleed mostly resolved the problem with ever climbing temps. At least it slowed the temp rise to a relative creep that was manageable by simply running the heater every once in a while. After running the truck hard for an hour, I let it sit and idle for 30 minutes with the climate controls turned off so that I wasn't doing anything to help the engine stay cool. During that time, temps continued to rise slowly and at the end of the 30 minutes they had reached 210*. (Not too bad, but still not quite where it was before the incident with the fan exploding...)

Sooo...I decided the smart thing to do would be to keep my hands off the cooling system until after Conclave. (I'll take my 180* t-stat and new water pump along just in case.)

BUT WAIT, THERE's MORE! Since I wasn't screwing around with the cooling system, I did a couple other maintenance type things to the back end of the truck.

When I brought it down off the lift and started it to back it out of the garage, something in the vicinity of the alternator was making a horrible rattle. (I could feel it though the alternator/bracket, but nothing was obviously wobbling or out of alignment upon visual inspection.) As it was late, I elected to try to drive it home, where it sat until last night when I headed back to my friend's shop.

In the interim, I consulted my local Rover specialist (another friend) and several other forums. Given my description and statement that nothing looked out of sorts, it was suggested to first pull the belt, and start checking the idlers, tensioner, alternator, etc. If all felt smooth, then it was suggested that there could be a bubble trapped in the water pump, or the pump could have started to come apart/fail. So, with the intent of checking all of this at the shop, I headed out yesterday evening. D2 rattling along just fine. I made it all of about a mile when this happened:


Having anticipated this, I had a spare idler and my tools with me, so I replaced it, trimmed the serpentine belt (the pulley had shredded one rib from it when it failed), and headed for the shop in rush hour traffic. Much to my surprise, engine temps stabilized at 188*, and only spiked to 201* when climbing long hills. This morning after make a couple short trips and getting the truck fully warmed up, I let it idle for another full 30 minutes with the climate controls off. It warmed to 188* and stayed there for the full duration of the test.

Here's my theory...troubleshooting this one was a problem because there were multiple contributing issues.
- Despite have bled the cooling system 3 or more times, there must have still been at least a small bubble(s) left trapped in it. I finally got those taken care of when I re-bled after replacing the top rad hose.
- The idler (which was relatively new having just been installed this past January), must have been quietly inducing drag on the system preventing the water pump and fan from spinning as hard as they should normally.