[BOBOCobra]

215 is kinda high for the "sweet spot", you have no cushion. Mine ran at 215 or so at ram on 80 degree days so I drove in traffic and shot the rad with a gun and there was a 30+ degree difference from inlet to outlet. That was way to much difference. I pulled the rad and it was full of gunk, either a bars leak or alumaseal type crap. I had to heat soak it and flush it 15 times and got half a small coffee can of crap out of it. that at least got my ram temp down to 190 and then I could do the rest. difference was then only about 10-15 degrees. inlet was 190, outlet was 175, ran about 195. It just seems odd you would need to stack rads on a street driven car, the back rad will be pulling hot air from the front rad... Have you made certain your rad is clean and you have no air pockets in the high pressure tank side? Water jackets are clean? Have you shot with a thermal for cylinder hot spots?