Is mineral oil the same as Dot brake fluid for hydraulic disc brakes?
No, mineral oil and DOT brake fluid are different and are NOT compatible.
The specific bicycle manufacture recommendations should be consulted and followed before serviced since a tiny amount of mineral oil introduced to a DOT brake fluid system will ruin the internal seals and can lead to internal corrosion, voided warranties, and unpredictable braking behavior.
Swapping the two types of fluids will damage the brake system and is not suggested. You should use the specific fluid that your bike manufacture recommends, and continue to only use that specific brake fluid type.
DOT & Mineral Oils are DIFFERENT & NOT Compatible
DOT Brake Fluids are glycol-based and are classified by a Department of Transportation DOT number up to a 5.1. The higher the number the higher the boiling point of the brake fluid.
Mineral oils are distillates of petroleum, which is a liquid by-product of refining crude oil to make gasoline.
Glycol-based DOT Fluids are NOT compatible with petroleum-based mineral oils and should not be swapped or changed out for each other.
*DOT 5 is silicone based and is not compatible
Types of brake fluid
DOT Fluid
Mineral Oil
differences between DOT fluid & mineral oil
There are several significant differences between DOT fluid and mineral oil, and I will discuss and breakdown the differences below.
DOT vs mineral oil & water absorption
DOT fluid is hygroscopic - This means that the fluid will absorb water. This is good since it absorbs moisture that enters the system, which will happen at some point
Mineral oil is hydrophobic - No water will be absorbed, which is good and bad.
Constant boiling point - Since no water is absorbed, there is no moisture to dilute the fluid, and lower the boiling point, as in DOT fluids. This is good.
Water pooling - Since mineral oil repels water, once water does enter the brake system the mineral oil will push water to the edges. Once this happens, the entire brake system is effectively operating at the boiling point of water, which is 212°F/100°C. This is bad since this fluid now has a low boiling point near areas that are susceptible to high temperatures, and could lead to your brakes locking-up.
This is the main performance difference between mineral oil and DOT fluid, and it’s a significant difference since over-time water finds its way into any brake systems.
Dot fluid vs mineral oil & regulations
DOT fluid is regulated and has a set of standards that must be met
Since these fluids are used in cars and trucks, the Department of Transportation regulates these fluids and they must meet the standards set forth by the Society of Automotive Engineers (SAE)
Mineral oil is NOT governed nor held to any specific guidelines
Can be good, since it allows for bike manufactures to create new and innovative brake fluids
No regulation also means no minimum standards, no consistency, and minimal compatibility with other brands of mineral oil
New DOT 3 brake fluid compared to used fluid. (Image Source: Wójcik)
Boiling point differences: DOT VS Mineral oil
Does DOT or mineral oil have a higher boiling point?
Generally speaking, both mineral oil and DOT fluid have similar boiling points, with some brake fluids reaching maximum boiling points close to 570°F or 300°C.
DOT Fluid: Boiling Point
This question is hard to answer, since there are 4 different DOT classifications, DOT 3, 4, 5, & 5.1, with each classification having a different dry and wet boiling point.
Also, each type has its own differences in boiling temperatures. Even though the DOT fluids are governed, and have minimum boiling point standards….they are just minimums and don’t reflect the actual boiling point maximums.
DOT 5 is generally not used with MTB or other bike braking systems since DOT 5 is silicone-based and not compatible with bicycle braking components.
Mineral Oil: Boiling Point
Most bike-specific mineral oils have a similar boiling point to those of DOT fluids. However, due to the unregulated nature of mineral oils, the range between different manufactures can be quite large.
It should be noted here, that both types have similar boiling points assuming that no water has entered the braking system. However, in the real world, water will always find it’s way into any brake system, and DOT fluid will make water part of the system (as opposed to pooling the water at the edges of the system as does mineral oil)
Click the picture to learn more
Is mineral oil non-corrosive & environmentally friendly?
It really depends on what type of mineral oil you're talking about.
If you're talking about the hydraulic system mineral oil that is used in all sorts of hydraulic systems around the world, such as machine tools, steering gears, and land, sea, and air transports, plus brake systems, then the answer is no.
Mineral oil is a non-biodegradable liquid made from a crude petroleum oil base that is first distilled and then refined to mineral oils. This type of mineral oil is toxic.
However, there are different grades and types of hydraulic fluids/brake fluids that are:
Biodegradable
Environmentally friendly
Non-corrosive
Non-toxic
Renewable
These environmentally friendly fluids are generally made from natural vegetable oils with special additives. However, these fluids are generally not called mineral oils.
These mineral oils that are being used in hydraulic bicycle brake systems are unregulated and have their specific formula. You will need to contact the oil manufacture to see if the mineral oil is truly non-toxic, biodegradable and environmentally friendly.
This is often the reason that people ask about switching from DOT fluid to mineral oil. However, you MUST stick with whatever brake fluid your bike was manufactured to use unless you want to replace the entire braking system or void your bike's warranty.
Price differences & availability
Compared to DOT fluid, mineral oil is expensive and more difficult to come by, unless you order online or purchase from a bike shop.
DOT fluid - Since DOT fluids are used in cars and trucks, its mass-produced (cheaper) and can be found in any big box store or convenience shops
Mineral oil - Often times costs at least double the price. Also, many bike companies that use mineral oil often use a proprietary formula, voiding your warranty if you use a different brand. It appears to me, that these bike companies are using this as an additional revenue stream.
Brake fluid storage life
Which has the longer storage life after opening?
One of the main advantages of mineral oil is its shelf life after opening. This is good since mineral oil costs much more, but you can use the whole bottle since it can be used indefinitely if stored properly.
DOT fluid - Since it absorbs water, once the bottle seal is broken it will start to absorb moisture from the environment. When you bleed your brakes, you should start with a fresh bottle, or use a bottle that hasn’t been opened for more than a few months….at the most.
Mineral oil - Does not absorb moisture from the environment. Once it has been opened it can be stored indefinitely
Dot compatibility
DOT 3, 4, and 5.1 are all compatible and can be mixed together since they all have the same polyglycol base.
DOT 5 is not compatible with the other DOT brake fluids, as it is silicone-based, and can NOT be mixed with the others.
Interesting note: Hydraulic brakes were invented in 1918 by Malcolm Loughhead, in his shop in California. Later, Malcolm and his brother changed the spelling of their last name to Lockheed and started the Lockheed Aircraft Company.
final thoughts
So which one is better? Whatever brake fluid your bike calls for is the best one.
Jesse is the Director of Pedal Chile and lives in Valdivia, Chile (most of the year). Jesse has a Master of Science in Health and Human Performance and is MTBer, snowboarder, and reader of nonfiction books and research articles.
Sources:
Cvengroš, J., Liptaj, T. and Prónayová, N. (2017). Study of polyaromatic hydrocarbons in current used motor oils. International Journal Of Petrochemical Science & Engineering, 2(7).
Gilles, T. (2005). Automotive chassis : brakes, suspension, and steering. Clifton Park, Ny: Thomson Delmar Learning.
Epic Bleed Solutions. (n.d.). What’s the difference between DOT brake fluid and mineral oil?
Majdan, R., Kosiba, J., Tulík, J., Kročková, D. and Šinský, V. (2011). The comparison of biodegradable hydraulic fluid with mineral oil on the basis of selected parameters. Research in Agricultural Engineering, 57(Special Issue), pp.S43–S49.
Owen, C.E. (2011). Classroom manual for automotive brake systems. Clifton Park: Delmar.
SRAM Technical Service FAQ. (n.d.). Why did SRAM choose DOT 5.1 over mineral oil? [online]
Wójcik, Marta. “Rheological Properties of New and Used Brake Fluids.” Acta Mechanica Slovaca, vol. 22, no. 4, 1 Feb. 2019, pp. 50–54, 10.21496/ams.2018.034.