OK, I'll be the one to disagree with everyone else. I ran a brass FMS 3 core with a Flex-a-lite with no problems. As a matter of fact I could turn the fan off on the highway and it would stick at 180 all day long. This was on a Procharger setup, and a NOVI 2000 setup.
I think you problem may lie somewhere else. The fact that the car is supercharged makes little or no difference while driving under normal conditions. Does the radiator put fluid in the overflow when it heats up? What about your t-stat.....how old is it?
Also, about your fan.....does it push or pull? You want it to pull, and it can easily be wired to do either without even realizing that you've done it. Check and make sure that it is drawing air from the front of the car and not the engine. I'd check this first since it's the easiest. Hopefully that's what the problem is.....easy fix.
