Could always switch to a liquid cooling system also.
Actually, I'm going to get some stuff integrated for longterm missions. Batteries and extendable Solar Panels being some of the things. As well as things for personal survivability.
Even with liquid cooling, that liquid's stored heat has to go somewhere. A fridge produces a lot more heat than it removes from the food inside - it can dump that heat into the surrounding atmosphere. If you read what I wrote about power stations, they use water cooling to cool the coolant. That's why they're located near coasts - so they can cycles seawater through their systems and get rid of heat that way.
The mech is doubtlessly already using a liquid (either super-pressurised water or gas pressuirsed into liquid) coolant system. It's coolign the coolant that's the problem, and the only way to do that is air, really.
Extendable fins might work, but they'd be fragile, highly obvious, and impratical in combat.
Heat sinks could do if you then ejected them from the mech, a la mass effect, but then you only have limited amounts of those.
G is attempting to contact y'all
Christ, man, give people a few sentences between each other. Yeah, people won't answer back instantly.
Ah, the benefits of fusion :3
I would imagine they actually suffer the same problems, to be honest, but they can be shut down more easily. I'm not perfectly sure though, I'd have to look iin to it. It's harder because fusion reactors doesn't exist outside the lab.