c5 overheating problem

One year ago at about 85K miles, my 2000 started to overheat. It came on suddenly. One day it was running fine, next day the temps skyrocketed into the red, even while driving on the freeway. I replaced the thermostat but likely did not purge (burp) the system properly and was still having the same exact issue. So, I replaced the water pump with a Bosch pump. I refilled and burped the system as instructed and bam, no more overheating issues. The car ran perfect as before. When the temp would hit 230, the fans would hit high and drop in back down to 220. While driving, it rarely would go over 200. I realize that if I had burped the system when I replaced the thermostat, it would have likely been fine and not needed the water pump. Lesson learned. The water pump was not leaking or making noise. When I took it off, it spun just fine and the impeller didn’t appear to be clogged. I replaced it anyway.

Now, again, at 101K miles, the car is all of a sudden overheating. Only this time, it will stay cool while driving, but then overheat in traffic. Once the temp hits 220, it skyrockets up past 240 and both fans turn on high but the temp will continue to slowly creep up to the red. I took the radiator cover off and there was a good amount of debris. I bought a long BBQ grill brush that would fit down in between the condenser and the radiator and brushed all that crap out of there and off the front of the condenser. I still had the same problem. Then I replaced the thermostat and burped the system. I still have the same problem.

If it’s debris still stuck in the radiator fins, wouldn’t I see temps gradually increasing over time instead of all of a sudden? Also, the water pump is only a year old. Now, this doesn’t mean it can’t fail, but I’m thinking that the radiator is possibly clogged inside and/or the fins are probably still full of junk that the brush didn’t get out. Both hoses are hot with the one near the thermostat being hotter as it should. The fact that it runs at normal temps while driving leads me to believe it’s not the pump.

I don’t want to spend money I don’t have to. From what I’ve described, what do you think it is? Radiator problem or the water pump again? Is there any way to clean out the radiator without pulling it? The fans appear to be turning on at the correct temps. I did the water pump myself and it was a bitch to get the gaskets lined up and a couple of the bolts back in, but an hour or so and many curse words, I got it all together. I used the opportunity to replace all of the idler pulleys as they were easily accessible with the water pump off.