OK, heres the cliffnotes:

New: Radiator, water pump, fan clutch, A/C compressor, and hoses within the last year.
Flushed several times since, good flow through the heater core, water comes out clear after each flush.

Problem: Engine runs fine at 210 with zero issues...untill i turn on the A/C or get on the freeway. After ectended time on the freeway the temp will spike for a few minutes then return to normal temp.

When the A/C is on it will run fine at 210 for a while then the temp will slowly start to creep up till it spikes. At this point I have to turn off the A/C and after a couple minutes it will cool back down.

Yesterday I flushed it again and put in a 180* t-stat. Now again, it runs fine at 180...till the A/C goes on, then its the same problem.

Also, all winter I was not getting any hot air, dispite good flow through the core (not sure if the two are related, but throwing out there incase they are.

Any ideas?

BTW: 2000 XJ 4.0 auto

Aux fan coming on ?

^^ Check This ^^
BTW, You should be running a 195 t-stat.

how are you getting the actual temps?
do you have an accurate guage?

R u positive rad is full to the top when the motor is cold? Fan shrouds intact/inplace? Any electric gauge that suddenly moves up/down sounds like an electrical/ground issue. Verified temp with a IR temp gun pointed at the stat cover? Running a/c on virtually any vehicle will raise coolant temp somewhat since the condenser (in front of the rad) gets really toasty itself......but overheat, no.

Yes, the electric fan is working. I am just going by the temp gauge on the dash and the warning chime when it spikes. Rad it defiantly topped off and I have been checking it periodically. As for the t-stat I wanted to go with a colder one to see if that changed anything. Which as long as I am not running the A/C it stays well below the 210 mark now which is where it used to stay.

i have the same problem in my jeep. i just got my jeep and havent had the money toi do a tune up on it yet . ill check the radiator