I have a '97 Concours with 88K that has overheating problems, I was hoping to get some insight from the loyal Cadillac bretheran. I recently had the water pump housing seal leak, and I replaced it along with the water pump(I also had the fuel rail line pop a pinhole leak, but that's another story!). Upon completion, I refilled the cooling system, but was unaware of the magic pellet requirement. The car performed flawlessly for a week, driving around town(LA). On the weekend I attempted to drive to Vegas for a wedding, and got about 100 miles before the car overheated. I was aware of the 'limp home' mode, so I drove about 4 miles at low speed to get it off the highway. I noticed that despite the coolant blowing out of the overflow hose that the left (exit) side of the radiator was cold. I figured that the thermostat was stuck, so I had it replaced. I also changed out the radiator cap also. The service garage also did a combustion leak check. I'd never seen this test before, they used a clear cylinder with some dye and placed it over the filler neck while the coolant was hot and boiling over. They had it on for about 30 seconds, and the dye didn't change color, indicating there wasn't a combustion leak. Was this enough time to tell? I am not sure, I've never seen the test before. Anyway, we replaced the 'stat and the car still overheated. To get it home, we gutted the old 'stat and drove very slowly, keeping the temp at mid-gauge. I didn't get any smoke out of the exhaust on restarts. My gut feeling is that the rad is gunked up, maybe due to my not adding the pellets. So, my question is, does anyone else have any insight or suggestions, and if my rad is gunked up, what is the best way to clean it out? Thanks in advance.