That comment about hydraulic fluid made me rethink my bleed kit

I overheard a guy at the Portland swap meet say he never bleeds road brakes with mineral oil unless it's Shimano's own stuff. I've used that aftermarket green fluid for 4 years on my GRX setup without issues, but maybe he's right about seal swell. Has anyone else run a cheaper fluid long term and actually measured wear or piston sticking? I'm genuinely curious if the $18 a liter premium is just marketing or real protection.

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1 Comment

parker1831mo agoMost Upvoted

That mineral oil comment has some merit, but I'd push back on the whole idea that cheap fluid ruins seals. The real issue is usually contamination or old fluid that's picked up water, not the brand name on the bottle, and I've seen plenty of bikes with 20 year old cheap fluid that still shift fine. If you're bleeding regularly and keeping the system clean, the $18 stuff is mostly paying for peace of mind, not actual protection.