Yes there are DOT 3's that have higher boiling points than a DOT 4. For example AMSOIL Series 500 synthetic DOT 3 has a boiling point of 525°F.
But when compared to the equivalent Amsoil synthetic Series 600 DOT 4 Brake Fluid, it has a boiling point of 580°F The equvlent DOT 3 is still lower. What makes the fluid a DOT 3 and not a DOT 4 is not just the boiling temp but also the hygroscopy and lubricating properties.


NO DOT 3 fluid will out perform the equivalent DOT 4 fluid no matter how you try to spin it those are the facts. That is like trying to say Mineral motor oils or Bias ply tires out perform synthetic motor oil and radial tires.

"the best advice is to stick with what’s in your system"
What he is referring to is about mixing fluids. and is saying what ever in your system it is best to stick to it. And is expanded upon in the next paragraph with "Changing classifications will alter the chemical composition, and the compatibility of components will be unknown. Therefore, when switching fluids, a full system cleanse should be performed"

Different classifications of Brake fluids should not be mixed as he stated. This directly pertains to mixing 3 and 4 LHM or Silicones as they have totally different compositions. On the other Hand Dot 4 and 5.1 can be mixed as they are same chemical make up just in different concentrations. Before the DOT 5.1 classification was legislated it was called DOT 4+, DOT4+ and 5.1 are basically the same thing.

Not upgrading brake fluids when the opportunity arises is just silly, it is like saying I'm sticking with Bias ply tires cause that is what came on my vehicle. Or I'm not going to use synthetic motor oil cause my car did not come with it. That is regressive thinking, and has no foundation in fact or the realities of the technical advancements that have been made.

DOT 4 is a superior fluid bottom line, it has a higher boiling point than DOT 3 with equivalent water content it absorbs water at a lower rate thus reducing corrosion in the braking system and extending the life of components , ester composition brake fluids like DOT 4 and 5.1 lubricate way way better than the full glycol DOT 3 ,this the main reason why DOT 3 cant be used in DOT 4 Systems, the ester fluids will extend the life of seals and other wear components in the system compared to DOT 3

You are trying to make point that DOT 3 is better than the equivalent DOT 4 and such is not the case under any circumstances. The ONLY advantage DOT 3 has is a lower viscosity at extremely low temps. And that difference is so small it has no impact on operation of the system. And could only be an advantage in race applications and for that there is DOT 4+

 

I think you're trying to separate the fly **** from the pepper. By all means, if that's your thing..

If you look at the data from several independent sources, it's clear that a high quality DOT3 is equal or better than contaminated DOT4 in terms of boiling point.

The important thing with glycol brake fluid is that it is changed/flushed periodically, I think we can agree on that. There is no practical difference between the two for the average person bombing around in their old truck. The folks who are pushing the envelope change brake fluid after every run, at $3 a bottle I think I can afford to change it every year in my slick. If there aren't any free range gluten free borate esters in the lines, I can live with that. See where I'm goin' with that?