brake fluid - which dot

[bird]

I need to sort the brakes on the new zed so I need to but some fluid. I know the recommended fluid is DOT3 but can I use the higher grades, such as DOT4, 5.1 etc.

Edited January 24, 2016 by bird

[Mondo]

I'd have said Dot 4, mate. That's what I plan to use in mine, unless someone tells me differently...?

[bird]

My understanding is that going higher is OK but not lower. But thought it'd be better to check first.

[AndrewG]

DOT 3/4/5.1 fluids are polyethylene glycol based, and are suitable for our cars.

 

DOT 5 is silicon based and is not compatible with polyethylene (DOT 3/4/5.1) fluids nor is not suited to ABS brake systems.

[bird]

Thanks. Just realised I put the dot5 in above. So if I had some dot 5.1 in already, would be be fine to top up with dot 4 or 3 as an example because they'll just mix?

[AndrewG]

If you have put DOT 5 in then you will need to flush the system out.

[bird]

Sorry, I confused things by writing dot 5 in the original post, I've removed it now.

 

This is hypothetical btw but what I mean is, if I had dot 5.1 in the car, needed to fill in up a bit, could then then use dot 3

[AndrewG]

Yes you can, DOT 3 will have lower dry and wet boiling point temperatures than DOT 5.1. By mixing the two you

will drop the boiling point(s) of the whole fluid but otherwise they are compatible.

 

Edited January 25, 2016 by AndrewG
Added chart (Ignore DOT 5)

[bird]

Thanks Andrew.