Is it okay to mix mineral oil?

My SLX brakes seem to be working without issue, but I have notice that if the bike’s been up side down whilst fixing a puncture on a ride, the levers seem to need pumping up again to firm up; I guess that there’s some air in the system (possibly from when I cut the hoses without re-bleeding).

I’m got some Shimano mineral oil (it’s several years old but I believe that it doesn’t deteriorate or absorb water) and I was wondering whether it’s okay just to top up the system from the lever and pump out any bubbles into the bleed funnel, instead of doing a full bleed. Will there be any issues mixing different (and one quite old) batches of Shimano mineral oil?

It’ll be fine. I wouldn’t mix different brands though (or use anything other than shimano oil in shimano brakes)

It’ll be fine, that’s what I normally do instead of a full bleed.

Thanks. I need to change the brake pads shortly,so I’ll do it then.

Unlike DoT fluid, mineral oil is not hygroscopic. So your “aged” shimano brake fluid should be fine.

If the fluid that comes out is black/dark and you’ve got enough fluid it’s worth doing 2 full bleeds.

I’ve also found if you leave the brake lever tied on, it encourages air bubbles up to the top of the system. I tend to leave mine “on” for an hour or so. Before i snip off the cable ties I tap the caliper, and then up the brake hose to the lever. I usually get a number of smallish bubbles come out then and the brake feels a lot better. You can also slightly undo the lever clamp (with the pot atached to the lever) and roll it back and forth -+45 degrees whilst flicking the lever to encourage any bubbles out.

So am I risking killing kittens when I use citroen LHM?

i raised a similar concern when shopping at my LBS for mineral oil for my xtr’s – they sold me aftermarket oil – I bought the brakes from them – and they assured me it wouldn’t effect the guarantee despite Shimano clearly stating only use their own branded oil ..

So am I risking killing kittens when I use citroen LHM?

Have search on here for an older thread. Many people (including me) stating they used a “compatible” mineral oil but the brakes don’t feel as good.

The compatible stuff I used (from halfords i think) is more viscous giving the lever a different feel. Also there is a chance the oil may react with the seals causing them to swell up.

This^^^

Shimano oil is a lot thinner. Mineral oil is such an ambiguous term, like having a cold.

Shimano mineral oil has a significantly higher BP than, other brands. Used some cyclo stuff (green) in my brakes last year in the alps and it was burned up after about 3 runs.