Mineral oil
Mineral oil is a petroleum-based brake fluid, used by Shimano, Magura and Tektro. Unlike DOT, it's hydrophobic: it repels water instead of absorbing it. That makes it non-corrosive (it doesn't harm paint or skin) and long-lived in storage. Its boiling point is somewhat lower (≈170–200 °C by brand). The critical point: it never mixes with DOT, and since there's no unified standard, each brand has its own formula (don't mix Shimano with Magura needlessly).
If your brake is Shimano, it runs mineral oil. It's friendlier —it doesn't corrode or absorb water— but just as intolerant of mixing.
What it is and why it's hydrophobic
Mineral oil doesn't absorb moisture: the little water that enters the circuit stays separate and settles at the lowest point (the caliper). So it doesn't degrade over time like DOT. The trade-off: if that water pooled in the caliper exceeds 100 °C on a descent, it boils suddenly and can cause total brake loss (vapor lock). It's non-corrosive, which makes maintenance easier.
Key data
What it fits
It goes only in brakes marked «Mineral» on the cap: Shimano, Magura, Tektro. DOT is never put in them: it destroys them. Across brands, though chemically similar, viscosities differ, so avoid mixing Shimano with Magura except in an emergency.
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Frequently asked questions
Can I mix mineral oil with DOT?
No, never. DOT dissolves the rubber seals of a mineral brake and causes leaks and total failure within hours. Each system uses its own fluid.
Does Shimano mineral oil work in a Magura brake?
In an emergency, maybe, since both are mineral, but it's not recommended: viscosities differ and change the lever feel. Use your brand's.
Why isn't mineral changed as often as DOT?
Because it's hydrophobic: it doesn't absorb moisture, so it doesn't degrade over time like DOT. Still, bleed it per the manufacturer.