What's up with DOT 4 brake fluid?

Joined
Jul 19, 2009
Messages
2,053
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.
 
Joined
Oct 13, 2008
Messages
14,867
Location
The Old North State
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?
 
Joined
Jan 25, 2013
Messages
911
Location
California
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.
 
Joined
Dec 16, 2011
Messages
2,016
Location
War Eagle
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
 

gathermewool

Site Donor 2022
Joined
Jan 9, 2009
Messages
9,341
Location
New England
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...
 

Johnny248

Thread starter
Joined
Jul 19, 2009
Messages
2,053
Location
Detroit, MI
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.
 

Johnny248

Thread starter
Joined
Jul 19, 2009
Messages
2,053
Location
Detroit, MI
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.
 

Johnny248

Thread starter
Joined
Jul 19, 2009
Messages
2,053
Location
Detroit, MI
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
 

Johnny248

Thread starter
Joined
Jul 19, 2009
Messages
2,053
Location
Detroit, MI
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. Amsoil Dot 4 Fluid 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. 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.
 
Joined
Dec 5, 2009
Messages
28,120
Location
Regina, Saskatchewan, Canada
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.
 
Joined
Mar 14, 2006
Messages
9,614
Location
Pennsylbammyvania
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. shrug
 
Joined
Aug 30, 2004
Messages
25,223
Location
CA
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.
 
Joined
Dec 2, 2002
Messages
6,388
Location
Washington St.
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.
 
Joined
Jul 11, 2014
Messages
2,387
Location
Paradise of Florida
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.
 
Joined
Dec 2, 2002
Messages
6,388
Location
Washington St.
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
 
Top