It really won't be clogged like a drain, but simply coated inside w/calcium or whatever deposits, this insulates the tubes inside & keeps them from radiating heat. Drain a little coolant out & look at the tubes for deposits. My 79 would run hot, the rad was rodded out 10+ yrs ago & had no leaks, it is 3 ft tall & 2 ft wide w/a 4 row core, good stat & fan clutch. I really just couldn't see it running hot w/that big of a radiator but it did. I really didn't want to buy a new rad($500+), but it solved the problem. Now it runs on the cool side.
