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DOT 3 vs DOT4 Brake Fluid Confusion


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The O&M for my 2013 states:

 

Never use different brands of brake fluid together. Also, avoid mixing DOT 3 and DOT 4 brake fluid, even if they are the same brand

 

Then under the recommended fluids specs:

Brake Fluid: HMVSS No. 116, fresh DOT 3 or DOT 4 brake fluid.

 

1. How do I know what came from the factory DOT 3 or 4?

2. What is the best choice of brake fluid to use for a complete brake fluid flush and refill?

3. I see some brake fluids that state DOT 3&4 on the bottle. What the deal with this?

 

Sorry for my ignorance on brake fluid...

 

Tristan

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Read this.

 

http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid

 

The reason to not mix DOT3 and DOT4 is that adding DOT4 to DOT3 just brings the whole thing down to DOT3 standards, you aren't getting the benefit of DOT4's higher boiling point because the entire system is not DOT4, and they don't want you to be misled that you have better fluid when only a portion of it is better.

 

You can interchange DOT3 and DOT4 for the purpose of topping it up, but when you do a full flush, you should fill the entire system with only one kind.

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No problem with DOT 4 in a DOT 3 system, but not the other way around.

 

Also don't do DOT 5.0, it's from what I know silicone-based and mixing that with other stuff might be a really bad thing.

 

DOT 5.1 is also an alternative.

 

Also see the Wikipedia page: https://en.wikipedia.org/wiki/Brake_fluid#Glycol-based_.28DOT_3.2C_4.2C_5.1.29

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Flush DOT3 and replace with DOT4.

DOT5 shouldn't be used in a street car as it requires a lot of maintenance (can damage seals).

DOT5.1 is overkill unless you're tracking your car.

 

When it comes to stuff like brake fluid and lubricants I love overkill!

 

And at least here it's often not possible to find DOT3 fluid, it's DOT4 that's the most common. It's even a lot easier to find 5.1 than 3.

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