I was going to ask this in the brake,tire and wheel forum, but thot it'd get buried too fast, so I'll ask it here: what is the difference between DOT3 and DOT4 brake fluid? I looked in the driver's manual and it says to use DOT3 for the brakes (non brembo) but I want to get the stoptech rotor/pad upgrade kit which comes with braided lines and DOT4 fluid. Will I die a horribly painful death if use DOT4 instead? thanx y'all!

-drew

 

Wet [old exposed to moisture ingression] and Dry [brand new in bottle] boiling points.

Each minimum standard has brands with differening boiling points.
Generally the higher the wet boiling point the better [and more expensive].

Racer don't care and go for highest dry points since they change brake fluid every day sometimes between races!

Street cars where fluid is not changed but every year should look to wet boiling points as a grade indication.

Valvoline Syntech Dot 4 is a good compromise for the street if changed frequently every year.

The worst boiling occurs 5-10 minutes after a hard series of stops.
A single 80-zero stop will only raise the calipers 150F so it take riding the brakes [mountains] or lots of a series to get it up there........even a single 140 mph stop won't quite do it gets close especially with used fluids........but it will boil after the stops when no cooling air or rotation.

If a brake fluid EVER BOILS it must be immediately be replaced......boiling changes chemical composition dramatically!!!

 

Just to add DOT4 standards exceed the standards of DOT3. I think in the manual it says to use DOT3 or higher. It doesn't mean that you should only use DOT3 and nothing else.

 

You'll be fine with DOT4. For normal street use, it's just more expensive, and you won't see a benefit (nor will you see a negative)

 

Thanks all! BTW, Q45Tech, you are my hero. I want to be just like you. But this tiny grasshopper still has a LOT of learning (and reading) to do! lol Thx again for all the input everyone. . .

-drew

 

Nothing spending 70 hours per week [for 6 years] doing just automotive related research won't accomplish. Tech stands for technical not a "technican" in the sense that I have a few Masters degrees don't turn wrenches for a living except on my cars. Where I have more time to do it RIGHT vs. rushed technicans.

Be careful of some ULTRA DOT 4 spec racing fluids they actually absorb mosture faster than middle priced brands because they know the fluid will be change prior to every race.

All about chemistry of Esters.

"But upgrading the fluid is not the whole answer. Unfortunately the hygroscopic nature of the ether based fluids means that they should be completely replaced at scheduled time based intervals (annually would be good) and that the system should be bled to replace the fluid in the calipers every time that it is overheated to the point of generating a soft pedal. Yes, the pedal will come back as soon as the fluid cools somewhat - but the boiling point is now reduced and the pedal will go mushy at a lower temperature the next time. Triple Damn!!!"

from:
http://www.stoptech.com/whitepapers/brakefluid1a.htm


At 6 months Valvoline Synpower will still have a 423F boiling point on average, Motul 600 will be at maybe 500F but cost 12 times as much roughly what the Synpower is brand new from an unopened bottle. Obviously exchange labor cost more than any fluid.........15 cents to $2 per ounce is the range for decent to ultra products in liter sizes.

 

Interesting read. . .thanks. Except now I AM concerned after reading these paragraphs:

"As a trailing note on the DOT ratings, if your car was designed for a particular type of fluid, 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 certain 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."

The fluid that comes in the "upgrade kit" is this:
Motul RBF 600 High Performance Brake Fluid, 593 degrees F dry and 420 degrees F wet boiling point.
I do want good performance, but don't want to compromise components wearing out faster for it. . .I don't know what to do now. LOL! I'll ponder for a while. . .

-drew

 

If your not going to race there's no need to use Motul RBF 600. It's just complete overkill for the street and you will have to bleed the brakes more often. If your worried I would recommmend using Valvoline SynPower brake fluid. It is more than enough for street use and has a good high boiling point of about 500 deg F. Plus it's a whole lot cheaper than the Motul.

 

Hmmm. .. I figured as much re: the overkill Motul fluid. I wish it didn't come with the kit, maybe save me a few bux! I'll call the guys at performance nissan and see if I can omit the fluid and give me a discount or something. . .thanks again for all the input everyone!

-drew

BTW, has anyone used these bleeders before? It doesn't look like they have any kind of membrane to seperate the air from the fluid while pressurizing. . .but they are much more expensive than the $19 hand pumps out there!