Just about to bleed my tech m4,s and only have dot 4 ,does it matter ? or will i kill them ?many thanks

All good, only real difference on the different dot fluids is their boiling point. Just don’t use mineral type brake fluids. You are good to go…

Erm, except dot 5. If you use this bad things will happen. Dot 4 and 5.1 are both fine (and mixable), 4 has a lower boiling point than 5.1.

I’m not sure I’d mix (sure my old Mono4’s manual says not to mix).

If you’re switching then I would purge the system of the old.

If I remember rightly from when I used to have a trackday car and looked at the relative merits Dot 4 normally has a lower boiling point but is less hydrophilic (absorbs less moisture) – hence why most normal road cars were (at the time) on Dot4 as it lasts longer SO LONG AS YOU DON’T REGULARLY BOIL IT.

There used to be a couple of higher quality and high boiling point Dot 4’s available that were better than the cheaper Dot5.1 so best of both but more £££.

All now bled ,they feel fine ,now to clean up b4 wife gets back ! thanks for speedy replies