Flex fans were banned from being used on autocross cars by the SCCA Solo group a few years ago. They claim too dangerous; I've raced with a couple different flex fans (thin and wide... wide gives better cooling a lot!) and never had a problem, but a clutch fan broke my water pump shaft a long time ago (30 years ago... so that's when I changed to the flex fan.. never any problem).. But, now the rules have changed to allow electric fans.. to be installed sooner or later on my car.