DOT 3, 4 5.1 application

[bonjo]

My 2002 car owners manual of my car specifies DOT 3. Perhaps DOT 4 did not exist yet.

Toyota only sells DOT 5.1 and confirms it is suitable for my car (RAV4 2003 with ABS).

My local garage uses DOT 4 and said they would not want to use 5.1 that I offered to provide, Toyota or not.

Is there a reason for not using the latest spec fluid in an older car?

 

[Rmay635703]

Usually you need to flush and clean brake fluid carefully to convert (depending on what you are converting from and to)

Each DOT has advantages and disadvantages, have never found one that is truly bulletproof

As for why a garage would only use a specific brake fluid I have no clue, could be a liability issue not matching the spec on the car and you then couldn’t top off a customers car without a fluid change.

Sounds like bs

 

[BMWTurboDzl]

DOT 3 ,4, and 5.1 are compatible. DOT 5 is the odd man out.

 

[SuperSalad]

My local garage uses DOT 4 and said they would not want to use 5.1 that I offered to provide, Toyota or not.

Is there a reason for not using the latest spec fluid in an older car?

if they are willing to make the jump from DOT 3 to DOT 4, I can't imagine their reasoning for excluding DOT 5.1

 

[andreigbs]

I doubt your 2003 can take 5 fluid, as it's completely different stuff than 3 or 4 (silicone-based). I think 5.1 is backwards compatible to 3 and 4, but not sure.

If you're just doing a brake bleed, stick to what the manual recommends. New correct fluid is better than old fluid any day; no need to spend on pricey stuff.

 

[SuperSalad]

I doubt your 2003 can take 5 fluid, as it's completely different stuff than 3 or 4 (silicone-based). I think 5.1 is backwards compatible to 3 and 4, but not sure.

If you're just doing a brake bleed, stick to what the manual recommends. New correct fluid is better than old fluid any day; no need to spend on pricey stuff.

DOT 3 is typically glycol ether

DOT 4 is typically glycol ether mixed with borate ester

DOT 5.1 is typically the same as DOT 4 with a higher concentration of borate ester

All 3 of those are compatible. OP isn't talking about DOT 5 SBBF

 

[Rmay635703]

DOT 3 ,4, and 5.1 are compatible. DOT 5 is the odd man out.

Compatible but pointless to mix 5.1 with 3 given you gain none of its “benefits” if any of the old fluid is left and Dot 4 is worse than Dot 3 as you have to change it all the time given it’s propensity to gobble more water.

Also worth noting some Dot 3 has higher temperature ratings than a typical Dot 5.1.

I’ve often wondered what the best Dot 3 was? Did they ever have something akin to synthetic brake fluid that lasted longer between changes, especially in an antique car. (Preferably not Dot 5.0 though)

My best guess for the ops situation
is the garage has a bunch of barrels of Dot 4 they want to use up or they get Dot 4 cheap in bulk.

 

[bonjo]

dot 5 is outside this discussion!

didn’t was to get into the debate with the garage about why yes dot 4 but no dot 5.1
has dot 3 got less water absorption than 4 or 5.1?

 

[Rmay635703]

dot 5 is outside this discussion!

didn’t was to get into the debate with the garage about why yes dot 4 but no dot 5.1
has dot 3 got less water absorption than 4 or 5.1?

Yes Traditional Dot 3 has lower water absorption than traditional DOT 4, back in the day DOT 4 was “performance “ related but you had to change more often

 

[SuperSalad]

dot 5 is outside this discussion!

didn’t was to get into the debate with the garage about why yes dot 4 but no dot 5.1
has dot 3 got less water absorption than 4 or 5.1?

I believe DOT 3 does have less water absorption, yes, but I don't know how marginal or large the difference is. DOT 4 and DOT 5.1 do have significant increases in boiling points (both clean and with water contamination) over DOT 3 though.

 

[Rmay635703]

I’ve often wondered what this dot 3 stuff is

Wilwood Disc Brakes 290-0632 Wilwood Hi-Temp 570 Degree Racing Brake Fluid | Summit Racing

Free Shipping - Wilwood Hi-Temp 570 Degree Racing Brake Fluid with qualifying orders of $99. Shop Brake Fluid at Summit Racing.

www.summitracing.com

 

[bonjo]

Thanks for your inputs.
The verdict seems to be less water absorption for dot 3 which agrees with:

https://www.autozone.com/diy/brakes/dot-3-vs-dot-4-brake-fluid

against the is dot 4 has higher wet & dry boiling points.

I think I’ll go with the supplied dot 4 and not peruse 5.1 nor 3 as I have it changed every 2 years

 

[930.engineering]

.
That Wilwood is surely not a typical DOT3 fluid. Not helpful for the discussion.

@OP, just use any DOT4, DOT4 LV or DOT5.1 fluid. You likely won't notice the
difference. It's much more important to change the fluid somewhat frequently.
I doubt differences in water absorbtion are even noticeable or worth speaking of.

What hasn't been covered so far are the different viscosity requirements. As far
as I remember DOT5.1 has to be thinner at very low temperatures than DOT4, and
DOT4 LV is even thinner. Or let's say less thick, since any BF is getting thicker with
decreasing temperature - just like engine oil. However this is likely not a concern
if you are living in the UK. Some manufacturers spec DOT4 LV (low viscosity) fluid
for better/quicker/smoother ABS valving response which helps keeping braking
distances as short as possible (in particular way below freezing).
.

 

[bonjo]

Agree. Water absorption performance drop is so slow and it’s mostly the pedal feel, that it’s unnoticeable. And in my experience never a safety issue.

however I have seen the effects of internal corrosion due my negligence so the regime it to renew fluid every 2 years.
i don’t think viscosity is a key here in the uk because of temperatures and the age of my car. But humidity is!

 

[UG_Passat]

My 2002 car owners manual of my car specifies DOT 3. Perhaps DOT 4 did not exist yet.

Toyota only sells DOT 5.1 and confirms it is suitable for my car (RAV4 2003 with ABS).

My local garage uses DOT 4 and said they would not want to use 5.1 that I offered to provide, Toyota or not.

Is there a reason for not using the latest spec fluid in an older car?

DOT4 existed back in 2002, and before that.

My VW MK4 Golf required DOT4 fluid (pre-ESP).

Toyota still recommends DOT 3 and 4 fluid even in the 2020's.

 

[UG_Passat]

.
That Wilwood is surely not a typical DOT3 fluid. Not helpful for the discussion.

@OP, just use any DOT4, DOT4 LV or DOT5.1 fluid. You likely won't notice the
difference. It's much more important to change the fluid somewhat frequently.
I doubt differences in water absorbtion are even noticeable or worth speaking of.

What hasn't been covered so far are the different viscosity requirements. As far
as I remember DOT5.1 has to be thinner at very low temperatures than DOT4, and
DOT4 LV is even thinner. Or let's say less thick, since any BF is getting thicker with
decreasing temperature - just like engine oil. However this is likely not a concern
if you are living in the UK. Some manufacturers spec DOT4 LV (low viscosity) fluid
for better/quicker/smoother ABS valving response which helps keeping braking
distances as short as possible (in particular way below freezing).
.

Toyota's don't require DOT 4 Class 6 (LV) brake fluid, except for the Supra, which is really a BMW which uses Continental/Teves/ATE ESP/ABS brake controller/pump

 

[930.engineering]

.
Who said Toyotas would require DOT4 LV?
.

 

[bonjo]

with the helpful comments from members and some on line info I got, I’m now better informed and leas confused!

my take home points are:
Dot 3 is less moisture absorbent
dot 4 and 5.1 despite being more absorbent provide better wet boiling point.
dot 4 has a higher viscosity than 3; how that affects different abs and stability controls, that’s another story!
dot 5.1 has a lower visc and higher wet/ dry boiling points compared to 4

i will have to make sure of a 2 yearly (max) fluid change intervals given our very humid climate specially if using dot 4 or 5.1

 

[wag123]

DOT 3 is NOT less moisture absorbent than DOT4, but DOT 4 does need to be changed more often.

Bendix provides an insight into the importance of Brake Fluid - Issue 12 | Bendix Brakes

www.bendix.com.au

"Often not mentioned is the effect of the different DOT 4 formulation on the brake fluid behaviour. DOT 4 absorbs moisture at a slower rate than DOT 3 but is more susceptible to suffering a drop in its boiling point.
Typically a DOT 4 brake fluid will suffer a boiling point drop of 50% once it takes in 2% moisture while a DOT 3 brake fluid would only lose 25% of its boiling point at 3% moisture contamination although it takes in moisture at a faster rate. This suggests that DOT 4 brake fluids offer more stability and safety for longer but would need to be replaced at the recommended OEM intervals before it suffers a substantial drop in boiling point."

 

[930.engineering]

.
@bonjo:
Remember most of what you listed are minimum requirements, not typical properties.
As an example there are DOT4 specced fluids with exceptional boiling points, however
they still don't meet DOT5.1 requirements just because they don't fulfill viscosity needs.
Thinking of Castrol SRF, Motul RBF600/RBF660, Ravenol RBF R325+ and the likes. Same
with DOT4 LV: sufficiently thin for DOT5.1 when cold, but not high enough boiling point.
.