I use blue threadlocker, here’s why…
When I was a kid, I once went with him to the lumberyard east of Pagosa Springs Colorado, as he needed some lumber for a job he was doin out there, back when he built barbed wire. I can’t remember what the lumber was for, but anyway, what is now the farm feed truck, was once his truck. It has a 24V Cummins, which also has a left hand thread fan clutch. He had just replaced it the other day, it was summertime and hot, and the truck had been getting a little warm cuz the fan clutch needed replaced. He said he got it tight, but when we rolled up to the lumberyard and he let off the accelerator pedal, there was a crashing noise, as the fan and clutch went flying into the radiator. That damn sure ruined our day… so that’s why, I’m paranoid about it unscrewing when it’s locked on from being hot, and decelerating.