That is correct, convection will keep coolant circulating while the tstat is open, even though the motor is stopped and the pump is not pumping.

 

I know this is quite old but I did indeed have a fiberglass flex fan explode in my face. I just finished dropping the engine back in and fired it up to break in the new cam. I was standing on the driver's side leaning into the engine compartment adjusting the timing, and manually operating the carb between each adjustment. After it was running smooth I cracked the throttle open to clean it out and thats when it exploded apart. Wasn't sure what happened after it hit me. All I could see was blood. Couldn't feel my teeth with my tongue, I thought they were gone. The largest piece hit me in the nose and a few other small fragments peppered my face. No safety glasses but thank god nothing hit my eyes. They stitched my nose up good. 12 stitches starting from the nose bridge down to just above my lip. I was extremely lucky that was all that happened! Needless to say I am a lot more safety conscious when the hood is open and the engine is running.

 

. X 2... the aluminum blades on flex fans eventually crack from flexing, break off, and go through the hood... the small print usually has some disclaimer like for 4000 RPMs max...


. The clutch has silicone fluid in it that engages at higher temps and slips at lower temps... the Hot Rod test claimed the stock blade with clutch cooled better than any of the others... and used less HP and blocked less airflow the rest of the time... the dual function clutches also have a bimetal heat coil on the front linked into the clutch that makes them even more temp. sensitive...

 

I recently converted from a factory Ford Flex fan to a Hayden HD clutch and 6 blade solid fan. It is louder than the flex fan but I got used to it quickly and don't notice it anymore. I have not noticed any other difference in cooling or power or MPG.