I filled my mountain bike brakes with baby oil for a year and here are the results!

Product reviewed

• Bike: Diamondback El Oso fat-tire mountain bike (mentioned for context).
• Brakes: Hydraulic mountain bike brakes
  • Front brake: filled with Shimano hydraulic brake oil.
  • Rear brake: refilled with baby oil for approximately 1 year.

Main experiment / premise

About a year earlier, the creator purged the rear brake and refilled it with baby oil, while keeping the front brake filled with Shimano brake oil.

The creator set out to answer:

1. Is baby oil the same as brake oil?
2. Is baby oil easier to obtain?
3. Does it work as well?
4. Is it cheaper?
5. Will it damage brakes?
6. Is it safe for the rider?

They also jokingly mention “infant safety,” but do not perform a real test.

What’s being compared (context)

• Tire/braking power context: The bike uses ~5-inch-wide fat tires—they can sound like “TIE fighters” when spinning—yet the brakes can still stop them “with the flick of a finger.”

• Brake design context: The brakes are described as run-of-the-mill hydraulic brakes typical of modern mountain bikes.

Findings (after 1 year)

1) Baby oil vs. brake oil

• Not the same.
• They share a similarity: both are mineral oil-based.
• Differences highlighted:
  • Viscosity differences
  • Boiling point differences
  • Brake oil “blends” vary by manufacturer
• The creator also notes (comically) that baby oil has a diaper-like smell.

2) Performance (does it work as well?)

• In the creator’s one rear brake test, it seemed to work just as well after a year.
• They emphasize limitations:
  • Only one brake, on one bike
  • Only one climate/elevation context
  • Manufacturer “torture tests” and real-world heat/piston temperatures could still show differences

3) Cost

• Baby oil price (assumed):
  • “Name-brand” baby oil: about $1/ounce
  • Cheaper baby oil: about $0.25/ounce
• Shimano brake oil price: about $1.30/ounce
• Possible hidden cost:
  • If you seek warranty coverage after using non-approved fluid, you could be denied
• They claim a full purge/refill (front + rear) with Shimano oil would cost under $1.
• They also note most riders likely don’t do full annual purges anyway.

4) Brake damage / internal compatibility

A mechanic (Squatch Bikes, Brevard NC) inspected the brakes after the purge:

• Front: Shimano brake oil
• Rear: baby oil

They compared seals and O-rings side-by-side and could not see differences.

Reasoning offered:

• Inside the system is mainly rubber + aluminum
• Baby oil isn’t considered chemically harsh

Still, they admit unknowns:

• Effects under high heat
• Performance at lofty elevations
• Long-term abuse outcomes

5) Safety for the rider

• The creator personally felt safe (“slept just fine”).
• They do not recommend it for others, because:
  • the test is unscientific
  • the scope is limited
  • braking performance is critical

Pros mentioned

• Easier to obtain: baby oil/mineral oil is available at a grocery store 24/7
• Potentially cheaper: if performance truly matched (though brake oil itself isn’t that expensive)
• No obvious seal/O-ring damage observed after the creator’s year-long trial (in this specific case)

Cons / risks mentioned

• Not actually the same as brake oil: differences in viscosity and boiling point, plus brand blend variability
• Warranty risk: could be denied for using baby oil
• Unknown long-term and high-heat performance
• Not recommended due to limited test scope
• Smell: explicitly noted (comic but repeated)

Verdict / overall recommendation (implied)

• Overall stance: don’t use baby oil as a brake fluid substitute.
• Rationale: even if it seemed to work in a narrow test, there’s no compelling need to risk brake reliability—especially since brake fluids depend on brand-specific engineering.
• Recommendation: use the correct brake oil for your brake brand (or at least a fluid designed for brakes).

Unique points mentioned (all)

1. Diamondback El Oso fat bike; tires about 5 inches wide.
2. Brakes can effectively stop massive wheels even when spinning.
3. Front brake remained Shimano oil; rear was baby oil for ~1 year.
4. Motivation: online claims baby oil can substitute for mineral-oil-based brake blends (Shimano/TRP/Magura).
5. Baby oil is mineral oil-based but not the same as brake oil (viscosity/boiling differences).
6. Baby oil is easier to obtain (grocery store vs ordering/brake shops).
7. Rear brake seemed to perform “as well” in a limited test, but heat/altitude could differ.
8. Cost comparison using per-ounce prices ($1/oz, $0.25/oz, $1.30/oz).
9. Warranty denial risk when using baby oil.
10. Claimed purge/refill cost with Shimano oil (front + rear) is under $1.
11. Mechanic found no visible seal/O-ring differences between fluids.
12. Unknowns remain for high heat, altitude, and long-term abuse.
13. Creator won’t advise others because braking is too important.
14. Diaper smell and “infant safety” are discussed humorously (not tested).
15. Final note: brakes ended up “devoid of any oil,” and they want to refill with the correct Shimano oil.

Speakers / perspectives (as described in subtitles)

• Primary creator (main speaker):
  • Leads the experiment
  • Asks the questions
  • Provides cost/performance claims
  • States the recommendation (don’t do it)
• Bike mechanic (Squatch Bikes):
  • Inspects seals/O-rings professionally
  • Reports no visible differences between baby-oil-filled vs Shimano-oil-filled components