brake fluid recommendations

[Dudi]

Used to put SRF in my fun road car (over 700bhp/ton and weighs 1750kg) but needed changing once a year and have used Motul RBF660 for the past couple of years. Absolutely no issues with repeated stops from over 200mph on runway days.

SRF also eats seals but for track use it is the ultimate.

[Dev]

 Not all brake fluids are alike even in their respective DOT ratings as there is so much variation. It is a common myth that you can always substitute one for the other except in the case of DOT 5 but not always.  There is also more to brake fluid in regards to its viscosity, seal and corrosion protection. 

Here is the white paper that is  published from Centric Parts that I will be quoting from.
https://www.apcautotech.com/getmedia/026dfcc4-906a-4f74-961d-4df6123cdca8/brake-fluid.pdf

I will also be quoiting from this article.
https://www.aa1car.com/library/bfluid.htm

  There are many cars where DOT 4 fluids are not compatible because the viscosity is just too thick for cold weather performance especially in applications where they use ABS and traction control mechanisms in colder climates. In cases like this they use low viscosity DOT 4 and other variants that were made to address this issue, they cannot use regular DOT 4 fluid.

DOT 4 fluid that is used in a car that was designed for DOT 3 can have other damaging effects that might not be apparent immediately due to its chemistry and viscosity.

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.

As far as DOT 4 being changed out early because its more hygroscopic than DOT 3 is a widely circulated myth. Actually it is the other way around.   

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. By FMVSS116 standards, DOT 4 fluids must have a minimum dry boiling point of 446F and a minimum wet boiling point of 311F.
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.

DOT 4 fluid, which has a higher minimum boiling temperature requirement (446 degrees F dry and 311 degrees wet) soaks up moisture at a slower rate but suffers an even sharper drop in boiling temperature as moisture accumulates. Three percent water will lower the boiling point as much as 50%!

From my own personal experience I was using DOT 4 and DOT 5.1 at some point in time. I actually bought a case of DOT 5.1.  I used it like regular DOT 3 as a daily commuter and about a year later when temps dropped I noticed that the pedal became wooden. I lost modulation and didn't know why. When spring came I went for a spirited drive and experienced brake fade in a bad way.  I also used the stuff for my clutch and I started having shifting problem from poor disengagement. Once I flushed the fluid I was fine for a time but the grinding returned. 

After going back to Toyota DOT 3 fluid the pedal was much better and I never experienced a problem like this ever again.  I believe the Toyota fluid offers the correct viscosity and corrosion inhibiters to keep the brakes in perfect order. Also I can go over 2 years with the fluid and never experience a lick of fade. 

  There is a good reason why DOT 3 fluid is used in most passenger vehicles simply because it's forgiving in real world conditions.  If you use DOT 4 fluid be sure to change it out early because the braking system is not perfectly sealed for DOT 4 and moisture enters into the breather and the seals of the pistons. Its further contaminated when you drive in rainy conditions which can easily drop the boiling point drastically for DOT4 fluid and give you a nice surprise when you need the brakes the most. 

In regards to racing I would just use fresh Toyota DOT 3 fluid until you notice brake fade, at that point in time you will know that going to DOT 4 was a necessary upgrade and a milestone.   

One more link in regards to boiling capacity.
https://cartreatments.com/dot-3-vs-dot-4-brake-fluid/

[shnazzle]

I guess my experience marries up to that with the DOT4. I guess it wasn't that it was more hygroscopic, but the heightened effect on the boiling point. In any case brakes felt sh1t. Flushed it with 5.1 and problem went away. That was over a year ago now and it still brakes absolutely fine, but there's nothing like the feel of a crisp, freshly bled brake system, so I'm flushing it soon and I got a good deal on the RBF so it's going in

Interesting read though. Next batch will be DOT3 I guess. Saves money too

[Dev]

I guess my experience marries up to that with the DOT4. I guess it wasn't that it was more hygroscopic, but the heightened effect on the boiling point. In any case brakes felt sh1t. Flushed it with 5.1 and problem went away. That was over a year ago now and it still brakes absolutely fine, but there's nothing like the feel of a crisp, freshly bled brake system, so I'm flushing it soon and I got a good deal on the RBF so it's going in

Interesting read though. Next batch will be DOT3 I guess. Saves money too

There is another good reason to use only Toyota brake fluid.  The formulation is specific for the seals and metals of the car. 

Although this does not effect our cars it has caused trouble when other Toyota cars and trucks used different brake fluid.

http://media.fixed-ops.com/Toy_Campaigns/a0m.pdf

 

During vehicle assembly, Toyota uses brake fluids containing polymers that act as lubricants for certain brake system components. If replacement brake fluid is used that does not contain such polymers, or contain only small amounts, a part of the rubber seal (Brake Master Cylinder Cup) located at the rear of the brake master cylinder may become dry, and the rubber seal may curl during movement of the piston. If this occurs, a small amount of the brake fluid could slowly leak from the seal into the brake booster, resulting in illumination of the brake warning lamp.
• If the vehicle continues to be operated in this condition, the brake pedal feel could change, and braking performance could eventually begin to gradually degrade. If the warnings provided by the lamp illumination and the change in pedal feel are not heeded, a vehicle crash could occur.
• Toyota original brake fluid which is applied at the manufacturing plant contains polymers and does not cause this phenomenon

Honda had a similar issue with corrosion using non Honda brake fluid. 

One of the most basic indicators that you shouldn't use DOT 4 fluid is on the reservoir cap which states use DOT 3 fluid only.  On some other Toyota cars they will state DOT 3 and DOT 4 compatibility. 

It is believed that although Toyota fluid claims meeting DOT 3 specifications it might actually exceed it and will be much higher.

There are a lot of hidden truths to fluids of all types.

[james_ly]

There is another good reason to use only Toyota brake fluid.  The formulation is specific for the seals and metals of the car. 

Although this does not effect our cars it has caused trouble when other Toyota cars and trucks used different brake fluid.

So any normal fluid works? Phew!

[Dev]

There is another good reason to use only Toyota brake fluid.  The formulation is specific for the seals and metals of the car. 

Although this does not effect our cars it has caused trouble when other Toyota cars and trucks used different brake fluid.

So any normal fluid works? Phew!

I don't think anyone knows however the formulation of the Toyota brake fluid was optimized for the car. There is a good chance that the seals and metals will last longer.  Honda makes it clear for their car that you should only use their brake fluid otherwise you risk corrosion.

Also there is a very good chance that Toyota bake fluid has a much higher dry and wet boiling point as it is advertised to be heavy duty and high temp. 
  It is also the factory fill and specified in the manual for the Lexus ISF, LFA super car and heavy duty trucks and SUVs.  If this fluid can handle those applications it should be more than sufficient for ours.