What happens if I mix dot fluid?

I have one set of brakes that want dot 4 only and another set that want dot 3 or 5.1. As far as I can tell the only difference is boiling points, so why be so specific.

As long as I don’t put mineral oil or dot 5(silicon based) in then why can’t I make some form of dot fluid cocktail to bleed my brakes with?

Pretty sure I’ve mixed them in the past
Not in the bottle but by simply using what’s to hand when bleeding etc.

You will be fine.

you`ll blow up!!!

Don’t mix it with swimming pool sterilising tablets.

Never have figured out why some products want only low end fluid, it’s common on scooters to insist on DOT3 only but 3, 4 and 5.1 are supposed to be fully compatible. Course you won’t get the full benefit of the higher boiling points.

DOT 3, 4 and 5.1 can be mixed, but the mix can only be considered as good as the lowest rated of whatever you use. DOT 3 typically has a BP which is around 50-70 degrees lower than a typical DOT 5.1.

I don’t know why a manufacturer would state “DOT 4 only”. Some DOT 4 fluids have a higher (dry or wet) BP than some DOT 5.1 fluids. I buy Motul 5.1 by the half-litre from motorcycle shops (it’s about £7) and it goes in every (DOT-based) brake I work on.

People top up brake and clutch reservoirs all the time on cars without knowing what’s already in there.

The ‘official’ line with brake fluid is that you can add a higher grade to a lower grade. I guess the reason they won’t say it’s OK the other way is that if a brake set-up is expected to generate an amount of heat that isn’t a problem with 5.1, then using 4 will cause problems sooner & brake problems are likely to be the most serious. I’d just use good stuff for everything where brakes are concerned. The only times I’ve had brake fade have been on long & really steep European descents after a few miles & lots of switchbacks. It’s unlikely to be a problem in the UK most of the time.

Sounds like you are asking if you can create a blend of fluids that you can then use in all your brakes. Theres no point, just buy a bottle of whatever and use that in all of them.

Depends on the proportions you use. Approx 50:50 mix of 3 and 5.1 will give you dot 4

I’m afraid not southern yeti, mix any grade with another and you can only get the lower grade, it’s all to to with the the boiling point of the brake fluid, see three fish answer

Northwind – Member

Don’t mix it with swimming pool sterilising tablets.
<hyper> WILL IT GO OFF WITH A BANG, WILL IT? WILL IT? <hyper>

What pool cleaning tablets to cause a mushroom cloud?

Brake fade is a different issue.
Trucks with air brakes can get brake fade.

Thanks for the responses, I think I’ll just go for it.

I just didn’t fancy buying a pint of each type, just stick to the 5.1 from now on.