General Tech Brake Fluid

[KVH]

Just trying to recall: Synthetic can be mixed with non-synthetic, and Dot 3 is preferred for TR4s but can be mixed with Dot 4? Right?

 

[CJD]

As far as I know, none of them should be mixed.

 

[bobhustead]

My original can of DOT 5 said just add it and bleed until purple squirts out. Many years, no problems, but you probably should take John's advice.
Bob

 

[NutmegCT]

From Valvoline:

Brake fluids can be mixed only if the fluid that you add to the system belongs to a higher grade.

For example, a braking system that has a brake fluid DOT 3 specification can use a DOT 4 or a DOT 5.1 fluid. Also, a system with a DOT 4 can be topped up with a DOT 5.1 without bleeding the system.

However, never top up a DOT 4 system with a DOT 3 brake fluid. DOT 3 won’t be able to meet the temperature requirements because of its lower dry and wet boiling points.

Once again, do not mix DOT 5 with any other type of brake fluid because of its silicone-based composition.

Vehicle Maintenance: Brake Fluid DOT 3, DOT 4, DOT 5.1, and DOT 5 - Valvoline™ Global Europe - EN

Brake fluid selection is a particularly important task of vehicle maintenance. Different types of brake fluids match the requirements of specific braking systems. The most common ones used today are DOT 3, DOT 4, DOT 5, and DOT 5.1 brake fluids. Are all brake fluids the same? If not, what is the...

www.valvoline.com

 

[poolboy]

I think all brake fluids are "synthetic" whether they are DOT 3, 4 or 5.1.....but DOT 5 is a little different animal from the other synthetics

Most brake fluids used today are glycol-ether based, but mineral oil (Citroën/Rolls-Royce liquide hydraulique minéral (LHM)) and silicone-based (DOT 5) fluids are also available.[1]

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[KVH]

Yes thanks; I figured that was the case.