Brake fluid mix

[old guys rule]

Can you mix dot 4 brake fluid with Dot 3 synthetic brake fluid?

 

[Don67Satellite]

Yes. I believe the only no go is dot 5 with others, however 5.1 supposedly OK.

 

[493 Mike]

I believe Rick Erenberg (Mopar Action) stated that DOT 5 would work with 3 and 4 as adding, even inadvertently, to a system could cause a braking failure that the DOT would not allow if an adverse reaction could occur due to chemistry. Anyone else read that statement by Rick?
Mike

 

[Don67Satellite]

Not sure about any Erehnberg specific quotes on it.

DOT 5​

DOT 5 brake fluid is a silicone-based fluid. Silicone-based fluid is hydrophobic, meaning it repels water. Moisture introduced into a brake system with DOT 5 fluid does not mix with the brake fluid. This causes the moisture to freeze or boil and can lead to brake fade.

Glycol and silicone-based fluids are NOT compatible. It is important not to mix these fluids. Only use DOT 5 in a completely dry system or in a vehicle that already has DOT 5 in the system. DOT 3, DOT 4, and DOT 5.1 are all interchangeable.

 

[old guys rule]

Not sure about any Erehnberg specific quotes on it.

DOT 5​

DOT 5 brake fluid is a silicone-based fluid. Silicone-based fluid is hydrophobic, meaning it repels water. Moisture introduced into a brake system with DOT 5 fluid does not mix with the brake fluid. This causes the moisture to freeze or boil and can lead to brake fade.

Glycol and silicone-based fluids are NOT compatible. It is important not to mix these fluids. Only use DOT 5 in a completely dry system or in a vehicle that already has DOT 5 in the system. DOT 3, DOT 4, and DOT 5.1 are all interchangeable.

Thanks guys

 

[Photon440]

I believe Rick Erenberg (Mopar Action) stated that DOT 5 would work with 3 and 4 as adding, even inadvertently, to a system could cause a braking failure that the DOT would not allow if an adverse reaction could occur due to chemistry. Anyone else read that statement by Rick?
Mike

I've read that statement by Rick, and he was incorrect. He stated that DOT 3,4 and 5 refer to boiling points only, and not whether or not they had silicon in them. He even said that some DOT 3 has silicon, which contradicts what the DOT requirements are for brake fluid. I like a lot of Rick's writings, but don't agree on this one.