What's up with DOT 4 brake fluid?

Status
Not open for further replies.
Joined
Jul 19, 2009
Messages
2,209
Location
Detroit, MI
I was at the store yesterday browsing and I couldn't help but notice that they had six different brands of brake fluid, and only one that was Dot4 spec'd.

The Valvoline Synthetic was the only one which stated DOT 3 / DOT 4. Everything else was DOT 3. Even the fancy bottle of Lucas. It seems to me that a few years ago most fluids were 3/4.

Is DOT 4 fluid becoming obsolete? Given the option, I don't know why one wouldn't prefer to use 4 over 3 given the higher boiling point.
 
Correct me if I'm wrong, but I'd assume that BF advertised as DOT3/4 meets the higher 4 specs. I'd think it's advertised that way because folk looking specifically for DOT3 aren't sophisticated enough to know DOT4 meets and exceeds DOT3.

Sound reasonable?
 
I was using Valvoline synthetic brake fluid but found it to turn dark relatively fast. I then started using Castrol LMA brake fluid which also turned dark pretty quickly. I have since changed to Wagner Dot 5.1 brake fluid which seems to stay the same color during my three year use.
 
Hello Kool1
Check your DOT 5.1 brake fluid and see if it says silicone fluid on it. If it does and you added it to a system with DOT 3 or 4, you have mixed chemistry in it now. If you did that you should do a brake fluid change out and put in the manufacturer spec fluid.
Let us know
 
Originally Posted By: toneydoc
Hello Kool1
Check your DOT 5.1 brake fluid and see if it says silicone fluid on it. If it does and you added it to a system with DOT 3 or 4, you have mixed chemistry in it now. If you did that you should do a brake fluid change out and put in the manufacturer spec fluid.
Let us know


3,4, and 5.1 are compatible.

DOT 5 is not compatible with the above for the reason you stated. The ".1" is the difference...
 
Originally Posted By: toneydoc
Hello Kool1
Check your DOT 5.1 brake fluid and see if it says silicone fluid on it. If it does and you added it to a system with DOT 3 or 4, you have mixed chemistry in it now. If you did that you should do a brake fluid change out and put in the manufacturer spec fluid.
Let us know


5.1 and 5 are not the same. 5 is the silicone based incompatible, and 5.1 is safe for 3 and 4 systems.

Awhile back I looked into switching to 5.1 but for some reason I decided to stick with 4. I can't remember why. I'll have to go back and look at it again. For some reason something about corossion or water attraction sounds familiar as to why I didn't use it, but don't quite me on that.
 
Originally Posted By: MolaKule
All brake fluids are synthetic.


What's funny about that is that Valvolines product description of their Synthetic DOT3 / DOT4 fluid on their website says:


•Compatible with all braking systems requiring a DOT 3 or DOT 4 fluid
•Mixes well with conventional fluids

Maybe I am reading that wrong, but seems to suggest they are misleading the customer into thinking that other fluids may not be synthetic.

BTW, is product the same as the SynPower brake fluid? I haven't seen it in years so I was assuming they just changed the name.
 
Originally Posted By: Johnny248
Originally Posted By: toneydoc
Hello Kool1
Check your DOT 5.1 brake fluid and see if it says silicone fluid on it. If it does and you added it to a system with DOT 3 or 4, you have mixed chemistry in it now. If you did that you should do a brake fluid change out and put in the manufacturer spec fluid.
Let us know


Awhile back I looked into switching to 5.1 but for some reason I decided to stick with 4. I can't remember why. I'll have to go back and look at it again. For some reason something about corossion or water attraction sounds familiar as to why I didn't use it, but don't quite me on that.


Just looking at boiling points, I think I stuck with the Amsoil Series 600 Dot 4 because the wet boiling (379°F) and dry (580°F) is a higher rating that 5.1
 
As far as fluid and color goes, here are a few pictures of some new and used Amsoil Series 600 DOT 4, as well as some Peak "Synthetic" DOT 3. You will notice that the Amsoil fluid is a darker fluid when new than the Peak which is nearly clear.

IMG_20140906_160326.jpg


Amsoil Dot 4 Fluid

IMG_20140906_160140.jpg

IMG_20140906_160052.jpg


These two pictures show the used Amsoil Fluid on the left (Aprox 36k, almost 3 years) and new Amsoil fluid on the right side. As you can see, this fluid starts off darker than some others. I don't know if it is dyed to look different, or something with the formulation.

IMG_20140906_160529.jpg

This last picture shows the used and new Amsoil on the top paper towl compared to new Peak Dot 3 on the lower paper towel.

This was meant to just show how the Amsoil has aged over the last three years. It still looks very good and clean to me. Also to show the difference between the two fluids when new.
 
Originally Posted By: Johnny248
Maybe I am reading that wrong, but seems to suggest they are misleading the customer into thinking that other fluids may not be synthetic.

They may be banking on that, but if one is giving them the benefit of the doubt, perhaps they mean a "conventional" fluid as in following the convention of being speced only a DOT 3 or a DOT 4, as is more the norm.
 
Originally Posted By: Johnny248
BTW, is product the same as the SynPower brake fluid? I haven't seen it in years so I was assuming they just changed the name.


The Synpower had slightly higher wet and dry boiling point specs than their current on the shelf stuff.

I am not sure, but I believe that their jobber only "Professional Series" fluid is the same stuff as their old consumer available "Synpower" DOT 4.
21.gif
 
I suspect that it is because most applications requiring DOT4 cannot take an over-the-counter DOT4 fluid.

Most of the DOT4 applications require a DOT4-LV fluid.
 
Quote:
why one wouldn't prefer to use 4 over 3 given the higher boiling point.

The same chemicals that give it the higher wet boiling point (borate esters) absorb moisture more readily. Changing it regularly is more important with DOT4 than with DOT3.

I was in the local NAPA franchise store a while back, picked up a bottle of the synthetic DOT4 brake fluid and took it to the counter. The parts guy, an experienced clerk there who is very helpful, asked me if I was sure I wanted the synthetic version. I told him that it was all synthetic, and the label was just marketing hype. I'm not sure he believed me.
 
Lacking selection of DOT4 around here too. Cheap sells.
Used to pick among 3-5 competitors for DOT4 fluid everywhere and now lucky if each store has one. Come to think about it, DOT3 selection is pretty lame too.

Pentosin canned DOT4LV is what I last bled with in my dailydriver. Prestone DOT3 in the weekender.
 
Originally Posted By: Greasymechtech
Pentosin canned DOT4LV is what I last bled with in my dailydriver.

Pentosin says:
"NOTE: Low viscosity brake fluid can be used in vehicles that do not require a low viscosity fluid; however, standard DOT 3 or 4 brake fluid should not be used for top off in vehicles that require a low viscosity brake fluid. This action will reduce the low temperature properties and decrease the safety performance of the fluid."
http://www.pentosin.net/f_brakefluid.asp
 
Status
Not open for further replies.
Back
Top