This is totally contrary to every DOT 3 and DOT 4 spec I have read. Everything says DOT 3 and DOT4 are 100% compatible, and that DOT 4 can be used anywhere DOT 3 is specified.
Can you show any articles or specifications that say DOT 4 shouldn't be used in any particular application where DOT 3 is specified?
These StopTech white papers are the only place I have read about the "possible" negative effects of Dot 4 borates in DOT 3 systems. These articles also throw out the ideas that boiling points drop off faster with DOT 4 and more frequent changes are recommended.
https://www.apcautotech.com/getmedi...ic-White-Paper-D5-Brake-Fluid-Basics.pdf
And this one:
https://www.apcautotech.com/getmedia/026dfcc4-906a-4f74-961d-4df6123cdca8/brake-fluid.pdf
"A seldom talked about characteristic though is that because of this chemistry, the DOT 4 fluid will have a more stable and higher boiling point during the early portion of its life, but ironically once the fluid does actually begin to absorb water its boiling point will typically fall off more rapidly than a typical DOT 3. "
"Does this make DOT 4 fluids better than DOT 3 fluids? Not always. Remember, the boiling points listed are minimums and there are DOT 3 fluids out there with higher boiling points than some DOT 4 fluids. The real differentiating factor should be that if you run a DOT 4 fluid you really should change the fluid more often than if you use a DOT 3, if for no other reason than the rapid fall off in boiling point with time. "
"As a trailing note on the DOT ratings, if your car was designed for a particular type of fluid (especially prior to the development of DOT 4 fluids), you should make every attempt to stick with that fluid! For example, if your car was delivered with DOT 3 fluid, the internal components of the system (seals, brake hoses, and fittings for example) were specifically designed and tested for compatibility with DOT 3. Because DOT 4 fluids contain a different chemical composition, the system may not necessarily react in a positive fashion to the borate esters floating around in the mix"
"
In other cases, just the difference in viscosity of the two different fluids may cause the seals to wear at different rates. What starts as an annoying squeak might eventually become a torn seal or worse. The examples could go on and on, but the message here is this: it's fine to upgrade from DOT 3 fluid A to DOT 3 fluid B, but you should think twice (maybe even three times) before switching from DOT 3 fluid A to DOT 4 fluid of any sort."
Just the messenger here. StopTech doesn't paint with the broad paint brush of BITOG - that DOT 4 is always better than DOT 3.
