symptoms of a plugged-up radiator?

[treed2 at wsu.edu (T. Reed)]

Hi all,

I'm moving to Arizona soon and since its typically a good 30-40 degrees 
warmer down there than Seattle, I've been thinking about whether my 16v 
has any chance of not overheating at every stoplight.

Lately it's been running a little hot for my tastes in mere 70 degree 
weather.. in the past it has tended to sit at or just above the LED, but 
lately on hot days it has crept up to 3/4 and doesn't seem to go down even 
when I'm moving at a pretty good speed.

Lots of new parts: water pump, low temp thermostat (87 deg C), heater
   core, heater valve, radiator fan motor, low temp radiator fan switch,
   expansion tank cap, lower expansion tank hose, 't' hose at front of block

I checked the engine's coolant passages when I had the motor out to put on 
the 2 liter bottom end and they were clean. There's a small hole drilled 
in the thermostat, and I already fought the air bubble battle when I last 
changed the coolant about two years ago. The radiator fan runs and seems 
to turn on when it should. I hosed all the dried plant matter and rocks 
out of the radiator fins when I pulled the A/C.

As far as I can tell, all that's left is the radiator itself.. but I don't 
know whether or not it's worth replacing just on a hunch. It would 
certainly be easier to do now when I'm set up to do it than down there.

But since it's a closed-loop system, I'm not even sure if my concern about 
warmer weather is a valid one - why wouldn't the thermostat just spend 
more time open?

Does anybody here have any first hand experience with plugged radiators or 
keeping roccos cool in hot climates that they'd care to share?

TIA

-Toby