The choice of pulleys is often overlooked when these fans fail. Many stock applications especially with A/C had large crank pulleys and small water pump pulleys thus easily exceeding the RPM rating for some aftermarket fans. All of my race car applications have run the small crank pulley which means even the engine I revved to 8500 would not have exceeded the 8000 RPM limit of the nylon Flex-a-lite had that car even been using a fan.