Brake fluid mixing

[Mr MXT]

Quick question requiring a quick answer.

Can you safely mix DOT 4 with DOT 5.1?

[budd]

the simple answer is yes they can be mixed, but for best results you should always try to choose the correct fliud for your application and only use new fluid from a seal container. That said mixing grades won't do any harm it will just comprise performance slightly

There's howerver a need for caution silicone based or DOT 5 marked fluids can't be mixed with regular Glycol based fluids, whilst it would be logical to assume the DOT ratings follow on ie DOT 3, 4, 5, and 5.1 this is not the case and DOT 5 is basically a different type of fluid and shouldn't be mixed with the others.

[//j17]

budd said:

There's howerver a need for caution silicone based or DOT 5 marked fluids can't be mixed with regular Glycol based fluids...

Actually there's not technical issue with mixing DOT5 silicone fluid with DOT3/4/5.1 glycol fluids.

It's not a sensible thing to do however as it's a worst of all worlds. You get the price, softer pedal and lower boiling point of DOT5 with the paint-stripping and water absorption of the glycol fluids.