Does Shimano mineral oil degrade?

Got an unused bottle in shed but it must be 8+ years old. I am going to shorten the brake hoses on my new bike and hopefully get away with not having to bleed it but will be good to have some just in case I do need to bleed.

Shouldn’t, as it’s just mineral oil.

You can also use Citreon hydraulic fluid instead (cheap from Halfords).
Shimano say not to, but I’ve had no issues in many years of using it.

mine is older than that and used just the other day actually.

No, it’s hydrophobic. Main advantage of mineral oil over dot fluid which is hysroscopic. Basically it doesnt absorb water from the atmosphere. Thats how fluid degrades.

Is guess if you left it on a shelf in direct sunlight it could also degrade over time, but generally no it doesnt.

8 years, low temperatures, no sun light is fine.
Like new.

It’s already millions of years old so should be fine. I bought one of those big bottles years ago and slowly working through it with no ill effects.

Citreon mineral oil is more viscous than the official shimano stuff.  It makes bleeding a little trickier.

Also mineral oils tend to have different additives put in them depending on the application.  Some (not necessarily Citreon stuff) may not play well with seals

Would i use it rather than Shimano stuff, No.  Would be OK if you were a bit stuck? Yeah.

I have a big bottle of simano stuff i bought 4 years ago and still have tons left.  Doesn’t seem to degrade.

Cheers all. Hopefully wont need it anyway!

it’s hydrophobic

Every day’s a school day, handy to know. Never had mineral oil brakes and now have a pair needing bleeding.

No, it’s hydrophobic. Main advantage of mineral oil over dot fluid which is hysroscopic. Basically it doesnt absorb water from the atmosphere. Thats how fluid degrades.

It’s a bit more complicated than that. A sealed container of DOT fluid should last for years too. Master cylinders and wheel cylinders are sealed from the atmosphere, but water can still work its way past the seals. With DOT fluid, the water will disperse throughout the fluid, so the boiling point will be reduced, but still be much higher than pure water. With mineral oil, the water will collect at the lowest point (i.e. the wheel cylinder) and drastically lower the boiling point exactly at the point where the heat is generated.

So, for storing an open container of fluid, mineral oil has an advantage, but DOT fluid is cheaper and easier to buy. For resistance to fluid boiling if you never replace the fluid, DOT fluid has an advantage. In practice, both work fine, I run old Hayes HFXs on some bikes and Shimano Deores on others, no problems with either.

If you’re caught short, the Halfords mineral oil works nicely too

If you’re caught short, the Halfords mineral oil works nicely too

I couldn’t swear to it, but every time I’ve used BikeHut Mineral Oil my seals have shit themselves within a few weeks (I know Shimano are known for that) whereas I’ve had zero failures since I bought a big bottle of Shimano oil a few years ago.

Not worth the risk IMHO.

I bought a litre in 2004. Might have to buy another one soon.
Still seemed alright last time I did a complete fluid change.