Mineral oil vs 5.1 silicone brake fluid

I don’t think you would get any appreciable improvement. Clutch slave cylinder doesn’t get as hot as brake where the piston is in direct contact with rotor. Can’t hurt though. As long as fluid isn’t contaminated with water and there is no air in system should be good.

If you change the oil type, be sure you clean the unit of all the oil as if they mix you could have some real issues. Use which ever you want to, but just don't let them mix.

Paw Paw

Dot 5.1 isn’t silicone based. Dot 5 is.

Curious - why are you considering this specifically?

I doubt the system seals are compatible with these different liquids

The risk when using DOT5.1 vs mineral is that if the slave cylinder seals go the dot5.1 will contaminate the gearbox oil.
Nitrile or Viton seals can deal with heat but only EPDM seals are safe for brake fluids.

5.1 has a higher boiling point, but I don’t see that being a benefit in a hydraulic clutch system. Extreme enduro or endurance races I could see it being used for the brakes, but I’m not sure on OP’s reason.

Take heed, people. DOT 5.1 is different from DOT 5.

DOT 5 is silicone, usually purple in color, and will not corrode paint or chrome.
DOT 5.1 is like "super" DOT 4 - it has a higher boiling point and is used in MotoGP racing for brake applications. Use it when VERY high heat is generated and/or you have extra money to spend for no reason. It won't really do anything except withstand more heat (and motocross bikes aren't heavy or fast enough to generate that kind of heat in almost all circumstances. Certainly not in a hydraulic clutch.)

Boiling points:
DOT 3: 400 Degrees F
DOT 4: 446 Degrees F
DOT 5: 500 Degrees F
DOT 5.1: 500 Degrees F