400 miles with a full fill of Hard blok You are a very brave man Mopar Dave. I had a 7 blade 18" flex fan in my Challenger for years when it had a 440 in it however when I installed the 505 my cooling problems started big time. The fix was a Smiths 2 core aluminum radiator with my old 7 blade flex fan from my previous set up. The motor cooled down quite a bit but still got too hot for my liking last year on Woodward ave during dream cruise. The fix was installing the factory original 7 blade clutch fan. The car has sat in traffic running in temps exceeding 80 degrees for over 20 min without even coming close to overheating I guess those Chrysler engineers knew what they were doing back in the day.