MINERAL OIL vs DOT 5.1

Mineral oil brake fluid is derived from petroleum and is composed of various hydrocarbons. It does not mix with water and is not glycol-based.

This offers several benefits, such as its extended durability and non-corrosive nature towards your bike's paint.

On the downside, mineral oil lacks regulation, resulting in variations in quality among different mineral oil products. Consequently, it's important to refrain from mixing mineral oils.

Furthermore, mineral oil is unlikely to cause skin irritation upon accidental contact, but for safety during brake bleeding, we recommend wearing gloves and eye protection.

DOT 5.1 brake fluid is a glycol-based brake fluid. It contains glycol ethers and additives to enhance its performance.

DOT 5.1 is more readily available due to its common usage in the automotive sector. It is also regulated in terms of its manufacture, meaning you get a relatively consistent product across different brands. "DOT stands for “Department of Transportation.”

You do not need to use mountain bike specific DOT 5.1.

It's essential to be cautious when handling DOT fluid as it can be corrosive and harm paintwork. When bleeding brakes with this fluid, it's advisable to wear appropriate protective eyewear and gloves. Any spilled fluid should be promptly wiped away with isopropyl alcohol.

Mineral oil is not hygroscopic, meaning it does not absorb moisture from the air. This can be an advantage in preventing water absorption-related issues in the brake system.

However, any water that enters the system tends to accumulate at the caliper over time, leading to decreased braking performance.

DOT 5.1 brake fluid is hygroscopic and can absorb moisture from the atmosphere over time. This can lead to a decrease in boiling point and potential brake system issues if not replaced regularly.

The wet boiling point is defined as the boiling point once the fluid has absorbed moisture from the air. Specifically 3.7% weight by volume. After this amount of water absorption takes place, the fluid is considered “saturated” and needs to be changed.

The dry boiling point is fresh brake fluid from a new unopened bottle, that hasn't been exposed to the atmosphere and had the chance to absorb moisture.

DOT fluid tends to permit the ingress of approximately 2-3% of its volume in water each year, and this percentage could be higher in excessively humid environments.

Depending on which mineral oil you are using, it can have a higher or lower boiling point than DOT 5.1

When DOT 5.1 fluid is in a dry state, its minimum boiling point is 270 degrees Celsius, but when moisture has penetrated the system (i.e., it's wet), the boiling point drops to 190 degrees Celsius. This is generally the same for all brands of DOT 5.1

PRODUCTS WE RECOMMEND

TECHNICAL DATA:

• Boiling Point (°C): 420

• CentiStokes @40°C: 8.56

• CentiStokes @100°C: 2.8

• Viscosity Index: 200

DATA SHEET

• The “Gold Standard”

• Pure plant oil

• Toxin free

• Not hazardous to water

• Completely biodegradable

• Very high boiling point

• Maximum compressive strength

• Low viscosity

TECHNICAL DATA:

• Boiling Point (°C): 215

• CentiStokes @40°C: 8.67

• CentiStokes @100°C: 2.84

• Viscosity Index: 202

DATA SHEET

• OEM Proven (SRAM)

• Easy to Source

• Similar viscosity to Bionol

• Similar boiling point to DOT 5.1

TECHNICAL DATA:

• Boiling Point (°C): 269 (DRY)

• Boiling Point (°C): 187 (WET)

• CentiStokes @40°C: -

• CentiStokes @100°C: -

• Viscosity Index: -

DATA SHEET

• Easy to Source

• Durable and reliable stopping power

• Anti-vapor lock formulation maintains responsive lever feel

• Resists corrosion, oxidation and “boil-off”

• Mixes with other DOT 3, DOT 4 and DOT 5.1 brake fluids

• Very low viscosity when cold

• High viscosity index (Low change in viscosity with temperature).

• Relatively easy to source

• Low cost

• The actual boiling point is unspecified. Flashpoint is 87°C.

• Special additives to reduce bubbles & foaming. This makes it very easy to bleed.