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In case you don't have 'original' bicycle specific brake fluid on hand (e.g. "Magura Royal Blood"), what might be a good alternative to use (in a pinch) in hydraulic (disc) brakes? (for brakes that take mineral oil).

How long would such an alternative last? Which problems might occur and how soon?

I've read a few suggestions for alternatives:

  • Fork cartridge oil (the lighter (more viscous) variant)
  • Total / Castrol LHM Plus Fluid ( I believe it's power steering fluid)

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Questions:

  • What are some alternative (/better) suggestions for alternatives?

  • Would the Total/Castrol LHM Fluid or fork cartridge oil be a good alternative?

  • Does anyone have experience with using either a fore mentioned options for brake fluid?

  • Would the heat generated by braking be an issue for either of these/other alternatives?

What are the requirements for a good braking oil/fluid?, my thoughts:

  • High boiling point

  • high fluidity

Do you agree with these requirements? Did I miss any or are some of them simply incorrect?

Any suggestions are welcome. Thank you!

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    The question is based on a lot of poor information and its premise is entirely flawed so it cannot be answered. LHM is widely discussed as a suitable, readily available alternate to Mineral oil. Mineral oil does not absorb water. If you are getting 'pockets' of water inside your mineral oil brakes, you got bigger problems than a bit of boiling water. DOT's boiling point lowers as it absorbs water, but it also does not get 'pockets' of water.
    – mattnz
    Feb 4, 2020 at 8:16
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    A nice article giving info about different types of brake fluid: epicbleedsolutions.com/blogs/articles/…
    – Andy P
    Feb 4, 2020 at 10:28
  • @mattnz thank you for your suggestions! :) I don't see how the general question "what are some alternatives to bike specific braking fluid " cannot be answered. Especially since I already got some suggestions. The premise (regarding water absorbtion) might very well be incorrect as you state, I got that from the forum post regarding using fork cartridge fluid as an alternative (it is linked in the question) and I explicitly asked in my question if someone could confirm this info to be true or false. If you could mention what else is wrong with my question I can try and improve it, thanks
    – Maarten -Monica for president
    Feb 4, 2020 at 12:05
  • @mattnz with "the premise is entirely flawed" do you mean the part about the "mineral oil absorbing water" part or am I misunderstanding? Also which of the information are you referring to as "poor" ? Thanks for explaining
    – Maarten -Monica for president
    Feb 4, 2020 at 12:10
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    I'd be curious what you mean by "in a pinch". Considering that hydraulic brakes are now standard, any bike shop will have the correct oil, so what is the scenario where you need an alternative? Are you thinking of emergency repairs on some wilderness trip? Many hacks on the internet seems more about not paying for expensive Shimano oil, which seems a bit risky...
    – Stephan Matthiesen
    Nov 1, 2020 at 9:27

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The rubber seals in mineral oil levers and calipers are very easily damaged by using the wrong fluid, and should this occur replacement seals aren't typically available. Experimenting with alternative or in-a-pinch brake fluids is a bad idea for this reason. The results are unpredictable. In the worst case, a brake failure could occur.

Running a different viscosity than intended can also alter brake performance. In particular, higher viscosity fluids have been known to sometimes cause either slower or incomplete piston return. Of course the specifics of the hose, brake, piston count, pad spring, etc are all going to play into that, a fact that no meathead MTB forum poster is ever going to consider for a hot second before telling you to go put LMH in your brakes just because they did it and it didn't blow up.

There's a type of DIYer who loves talking about how they've had their bike set up with hack X for Y years and it's totally fine, so it of course will always be fine for everyone forever. That's a good type of person to categorically ignore. Most of the time, their shadetree nonsense doesn't work as well as they want to believe, and they're really only out to appear as though they have something meaningful to contribute, when in fact the opposite is almost always true.

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Seth from "Seth Bike Hacks" youtube channel did a test recently with a baby oil, including disassembling the caliper and checking the seals for damage under a microscope. Full video here.

Also I remember reading in a review of Shimano brakes on bikeradar that in a post-crash pinch they used olive oil and got down the mountain OK. But this is rather an extreme example.

The only substitute I have a personal experience with was using sewing machine lubrication oil in very old Magura brakes as a long-term replacement. It did not seem to damage the brakes, but for some reason required bleeding the breakes much more often. It is possible that it was slightly out gassing under temperature. This is also what I would be most afraid of when using replacement - brake fluids are specifically engineered to avoid that, and it leads to mushy feeling on the lever.

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  • Since brakes may decide over life or death I believe the best alternative is to use the correct fluid. You wouldn't replace brake cables with fishing line.
    – Carel
    Feb 5, 2020 at 14:29
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    @Carel, the main difference here is that baby oil is mineral oil.
    – JPhi1618
    Feb 5, 2020 at 17:07
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    I'd add that per Wikipedia, mineral oil is "... any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum ..." That implies that different types of mineral oil could have different chemical formulae - higher alkane simply means 9 or more carbon atoms, and nonane through hexadecane (16 C atoms) appear to be liquid at standard conditions. So, to @JPhi1618's point, baby oil can be both a mineral oil and yet be different from Shimano's oil or Magura's oil. Different mineral oils might have different chemical properties.
    – Weiwen Ng
    Feb 5, 2020 at 23:07
  • That said, I'm slightly amused by the anecdote about filling a line with olive oil in a pinch. I noted in some quick research that Shimano mineral oil has a manufacturer-reported boiling point of 280 degrees celsius (536 Fahrenheit). The boiling point for olive oil is reported to be ... 570F / 298C, so pretty close on that parameter! (NB: if you Google this, you'll see that the smoking point for olive oil is considerably lower, but that describes the temperature when oil exposed to air starts to smoke, so not relevant in a hydraulic disc scenario).
    – Weiwen Ng
    Feb 5, 2020 at 23:10
  • @JPhi1618: Really, look at the composition of these cosmetics: mostly water. Would you put engine oil (mineral oil) on your little one's bottom? And if there's water it will boil and produce steam.
    – Carel
    Feb 6, 2020 at 18:59
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LHM is a very good brake fluid. It's used (was used) in the braking, suspension and steering systems of top-end Citroen cars and has a very high specification for an oil. Citroen specified that you could use SAE30 oil as a temporary replacement/top up where necessary. Certain aftermarket cycle mineral oils sold by eg Weldtite/Cyclo appear to be LHM with the green dye. It functions very effectively in Shimano, Tektro and Magura systems.

Shimano mineral oil didn't have its full specification published last time I looked. Presumably it's available somewhere. It looks and behaves like agricultural grade hydraulic mineral oils.

The Magura Royal Blood is vaguely mysterious. There was a Citroen specialist in Holland that used to use a blue mineral oil as an "upgrade" for the Citroen hydraulic circuit that was otherwise used in aeronautical hydraulic applications. I believe it had better flow and made the suspension softer. I wouldn't be surprised if Royal Blood was the same stuff, but it's purely speculation.

If you wish to maintain your warranty, guarantees etc, you must use the manufacturer specified fluid. There is little practical benefit in using the wrong fluid, though there are various options to use when you have no other choice. I wouldn't use vegetable oils as these are usually quite acidic and will eventually affect certain seal materials. Just ask the people using veg oil instead of diesel.

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Well I've used mineral oil and olive oil in simple brake levers that are on equipment.

One of the advantages of mineral oil and some of the substitutes I've used is that they are a Lot less corrosive than hydraulic fluid and in most cases cheaper to buy.

One thing I was told by a couple of manufacturers is that regardless of what you use, that it was extremely important to flush the system and not to mix different types of fluids together. Mainly for viscosity issues along with the corrosive issue's that may arise when not using manufacturers recommend fluid.

If you do use something different always replace all the fluid at same time regardless if you're leaking from a crack or a seal or whatever else is the issue. Mixing oils doesn't help. Just replace it all with new oil even if it's not what you were looking for but does work in the short term for sure and had no ill effects after having swapped from original to olive oil.

I had an emergency when nothing was open at 1 am and even though it was continuously used for next 5 days around 15 hrs a day. There was never an issue during operation with Olive Oil.

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  • The water in olive oil didn't harm anything?
    – DavidW
    Apr 17 at 23:12
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Regarding the answers that disparage even looking for an alternative, they show a misunderstanding of product composition and performance. What matters is the composition of the lubricant base-stock and the additive package. These together determine all of the performance characteristics. You shouldn't replace a mineral oil hydraulic fluid with a "DOT" power-steering-fluid type material and vice versa. If you can find a mineral oil hydraulic fluid with similar viscosity to Shimano's, then you should be fine. I doubt if there are any additives in this stuff since it is a low-stress application compared to pumped and high temperature machine/automotive applications and you can easily change it out every couple of years or so. If the bike industry wasn't so mysterious and with a lack of standards, we could have multiple suppliers of this material. It would be nice if someone measured the viscosity of Shimano BF and published it.

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If you can't get your hands on hydraulic oil the best replacement is mineral oil , I would absolutely not suggest using brake fluid because it is a major corrosive and will eat through the small metal and plastic parts . I also would not suggest motor oil because it will thicken as it cools and will gum up your brake lines.

Your brakes are the most important part of your bike so you have to be able to put your trust into them so you don't want to cheap out by putting trash oil in your braking system. Remember you get what you pay for so if you cheap out and hurt your machines you did it to yourself by using cheap alternatives.

Hydraulic fluid or mineral oil only.

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