2nd GDI 3-core Radiator gone bad?

A little more than a year ago, I replaced the GDI 3-core the PO had installed with a fresh one (now can't find the warranty papers and radiatorbarn "has no record") - I guess it doesn't matter since I'm of the opinion the last two were never that good to begin with. . .

Last time, I replaced radiator, hoses, thermostat, fan clutch, both temp sensors, flushed, burped and used 50/50 anti-freeze and distilled water. It was marginal at best, still ran warmer than my other two XJ's and they are both overdue for a radiator service.

This time after having it out for 2 months while I put in the a new engine, I put in an OEM thermostat, OEM lower hose, a 2000 auxillary fan, and heater hoses before filling it up again with 50/50.

Now, I'm running about 215-220 when it's 50-70 degrees out (my other 2 XJ's run a little under the 210 line in these temps). Checked the temp at the thermostat housing with a laser and it read 213 when the guage was about 215, and I've had the Aux fan kick on a few times too. Yeah, I know 210 is "normal" but, this ain't gonna cut it in the summer pulling grades in 108 degree heat. . .

Before I buy another radiator (NOT GDI. . .) any ideas?

50/50 AND distilled water? ? i hope it was just to "top it off". 50/50 doesnt need water.

new engine? how so? brand-new still in the break-in period, or a "new" used engine? a new engine tends to run a bit hotter in the break-in period due to the increased friction of the new parts seatng and wearing in.
just because it runs a few degrees warmer than other similar vehicles doesnt mean it has an issue. i replaced my cooling system last spring with a GDI and converted to the open system and it ran exactly the same temp as before. i added a bottle of Water Wetter and it dropped the normal running temp about 8 - 10 degrees.

50% anti-freeze / 50% distilled water (sorry I wasn't clearer).

The engine is new, I've put about 350 miles on it. I've heard a new engine will run a bit hot during the break in - how long is that?

Seems like it has always run 10 - 15 degree's hotter than the other 2, which rarely get over 210 except on really hot days.

Considering the list of parts I've replaced (oh yeah,the cat converter was replaced last year too), it just seems like it should be able stay at 210 or a litle less when it's only 50 outside. Just worries me with what it will do during the summer.

If a radiator don't leak or get plugged up with crud, it can just go bad.

If a radiator don't leak or get plugged up with crud, it can just go bad.
A 3-core will run hotter at low speeds than a good 2-core.
Its harder to get air through a 3-core than a 2-core plus the air is hot by the time it gets to the third core.
New engines just seem to run hotter because the heat is actually getting into the water with the nice clean passages.