I have boiled fluid on two systems.
Formula hydro 100% failure at 61 mph road tandem. Not good!
Also old Hope 4 pistons on mtn tandem. Also not good coming down Columbine at Leadville.
Both designs have incorrect pistons that do not keep the heat from getting to the caliper body.
Modern designs have addressed this.
Hope now uses phenolic pistons and Shimano ceramic pistons.
Crazy that bike industry did not learn from motorcycle industry early on. They figured this out eons ago. Guess they had to reinvent on their own.
Happy now with Shimano Zee on mtn tandem and Shimano also on road as well as a custom BB7 set-up on other road.
Can even run sintered metal pads with the correct new systems. Life is good.