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I have Magura hydraulic brakes on my bike. As it is hard to find the original fluid, I'm considering an alternative mineral oil for the replacement.

I'm taking my chances to damage my system if the fluid has inappropriate properties. So I will try in rear brake and see how it goes.

Question is, how much time should I wait before deciding the alternative brake hydraulic is inappropriate or not? (An hour? A week? A month? A year?)

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    Hi, welcome to bicycles. I would say it depends on what your alternative is; if you're using another mineral oil for bicycle hydraulic brakes (like anything Shimano-compatible) it should be fairly safe.
    – DavidW
    Commented Feb 18 at 15:54
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    I think the question you want to ask would be more about which kind of issue you can expect from using incompatible brake fluids: would the brakes "brake less" from day 1, or would they get damaged over time by using an incompatible brake fluid? And if so, after how much time would you be able to notice?
    – pqnet
    Commented Feb 19 at 14:00
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    Don't sweat it. I've used car hydraulics mineral oil in my Shimano-s for a decade and never had a problem. Also costs nothing in comparison.
    – Vorac
    Commented Jul 6 at 16:52

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According to both OEMs (Sminano/Magura) their brake fluids are incompatible (source: https://bikerumor.com/tech-speak-brake-fluid-break-down-and-implications-for-road-disc-updated/)

However there are multiple sources on the interwebz stating that people have used Shimano oil in Magura brakes without any performance degradation.

Source2: https://www.reddit.com/r/bikewrench/comments/czprxl/has_anyone_used_shimano_mineral_oil_in_magura/

Source2: https://www.rotorburn.com/forums/index.php?threads/magura-brakes-with-shimano-oil.313508/

Source3: https://singletrackworld.com/forum/topic/shimano-and-magura-brake-fluids/

While reading the above, I also found that mixing Shimano lever with Magura caliper is called Shigura

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  • So, there is no one ever experienced such a destruction for using different brand mineral oil, so there is no "expected destruction time window"?
    – ceremcem
    Commented Feb 19 at 5:30
  • I think the question is whether/how seals and gaskets react to the oil. Without more information about the composition of both. I think we'd be guessing.
    – keshlam
    Commented Feb 19 at 15:18
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    @ceremcem that "no one ever" is a high ask... Even if one finds no articles about that online, people might experience brake failures even when using original brand of oils, and one would have to be very experienced (and motivated and rich) to do postmortem analyses of exact root cause of brake failure (and that is assuming the rider survived the crash to be able to talk about, and assuming they were 100% sure that the oil caused the crash and were more willing to talk about that instead of trying to collect insurance money). So the best one can do is do an educated guess, really.
    – Matija Nalis
    Commented Feb 19 at 15:38
  • Will wrong fluid causes the failure instantly, or slowly? May my brakes work great at a time and instantly fail after 20 minutes?
    – ceremcem
    Commented Feb 20 at 15:57
  • If wrong brake fluid will damage your brakes it will most likely damage the seals. In that case, the deterioration will be gradual and actual failure may be very sudden (usually when you apply the brakes). But it is hard to say how long it will take to damage the seals. Could be days weeks months or years.
    – Art Gertner
    Commented Feb 20 at 22:47

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