Are all DOT3 brake fluide compatible?

Status
Not open for further replies.
Joined
Jul 18, 2016
Messages
162
Location
Canada
Hi guys. I'm not very familiar with brake fluid so I have a noob question for you. Are all DOT3 brake fluid compatible? If the answer is yes, are all DOT3 the same quality? I need to bleed the whole brake system of my car. For this I need a great amount of brake fluid. A local auto parts store has brake fluid on sale this week. their brake fluid is three time cheaper than the dealer. But before buying their brake fluid, I want to make sure that there is no compatibility issues, different specifications or quality standards like in the realm of engine oil. thx
 
They're not all exactly the same, but to meet the DOT spec they all have to meet minimum requirements. They should all be compatible, and having fresh fluid in there is better than having 10 year old top of the line fluid.

The differences in quality generally are only going to apply at the harsh end of the spectrum, if you were racing, or somehow regularly putting tons of heat into the braking system. Otherwise you're not going to see much difference.
 
If you do not race your car then you are not likely to notice an improvement by purchasing a higher end brake fluid. You could upgrade to DOT4 since it's chemically compatible with DOT3. I'd still go with the bulk 32oz store brand stuff and get in a habit of bleeding your brakes yearly with fresh stuff.
 
DOT3 and DOT4 are compatible. But if you mix them, you wind up with some unknown DOT3 + mixture. DOT 5 is silicone brake fluid and is not compatible with either DOT3 or DOT4. I had to look up the DOT 5.1 specs and had assumed it was a silicone based fluid, but its a glycol based and can be mixed with DOT3 and 4.

This link has a nice chart that quickly shows what can be mixed together, and seems legit. https://www.epicbleedsolutions.com/resources/faq/difference-between-dot4-and-dot51-brake-fluid/
 
No is not for racing. My car is a beater. One of the brake line was ruptured because of the rust. So I need to bleed the whole system. I usually buy just one bottle of brake fluid from the dealer for the "maintenance" bleeding. But since this time I need a great amount of brake fluid, this is why I'm thinking another option.
 
As already said, all DOT 3 and DOT 4 are compatible with no problem. One quart is usually enough to bleed the whole system. And speed bleeders are awesome
smile.gif
 
Valvoline's DOT 3/4 brake fluid is a good all around choice with a high dry and wet boiling point, that way if there is still moisture getting in the system you won't end up with soft brakes or severe fade. The dry/wet BP is just a few degrees under the 5.1 spec, it supposedly has extra anti corrosion additives and it's widely available and reasonably priced.
 
Originally Posted by slacktide_bitog
As already said, all DOT 3 and DOT 4 are compatible with no problem. One quart is usually enough to bleed the whole system. And speed bleeders are awesome
smile.gif




I'm not sure one quart is enough. The rupture of the brake line was so significant that the master cylinder was emptied.


Besides of all DOT3 brake fluids need to met DOT specifications, do they have different qualites like engine oil (synthetic, anti-corrosion, anti-moisture etc)?.
 
Last edited:
You will probably find that a quart of brake fluid is enough. Yes a lot of it is used to fill the reservoir but there really isn't that much used to fill the brake lines themselves.

You do not need some special quality fluid, just get standard DOT3 available at any auto parts store as the house brand or whatever is the cheapest major brand, or DOT4 or 5.1, just not "DOT5".
 
Originally Posted by ST2008
Originally Posted by slacktide_bitog
As already said, all DOT 3 and DOT 4 are compatible with no problem. One quart is usually enough to bleed the whole system. And speed bleeders are awesome
smile.gif




I'm not sure one quart is enough. The rupture of the brake line was so significant that the master cylinder was emptied.


Besides of all DOT3 brake fluids need to met DOT specifications, do they have different qualites like engine oil (synthetic, anti-corrosion, anti-moisture etc)?.


The main difference between different DOT 3 products is the wet and dry boiling points. The higher the number the better. There are minimum levels that all DOT3 products have to meet so any DOT3 product will be fine, it's just that if you have a choice, get the one with the higher boiling point. DOT4 is even higher, but the price tends to be a bit more and if it's a beater, DOT3 will be fine. A quart is usually plenty to bleed the entire system even with an empty master cylinder, they don't typically hold that much fluid.
 
Originally Posted by ST2008
Originally Posted by slacktide_bitog
As already said, all DOT 3 and DOT 4 are compatible with no problem. One quart is usually enough to bleed the whole system. And speed bleeders are awesome
smile.gif




I'm not sure one quart is enough. The rupture of the brake line was so significant that the master cylinder was emptied.


Besides of all DOT3 brake fluids need to met DOT specifications, do they have different qualites like engine oil (synthetic, anti-corrosion, anti-moisture etc)?.


Just as a point of clarification, if you see the work "synthetic" on a bottle/can of brake fluid, ignore it. All brake fluid is synthetic by definition. They're all made by a chemical and not a refining process. But by the same standard soap is "synthetic" since it's a chemical process of synthesizing soap from a fat. So is shampoo since detergents are synthetic chemicals.

The standards are published by the US government as part of Federal Motor Vehicle Safety Standard 116 (49 Code of Federal Regulations 571.116).

https://www.govinfo.gov/content/pkg/CFR-2011-title49-vol6/pdf/CFR-2011-title49-vol6-sec571-116.pdf

They set the minimum dry and wet boiling points for DOT 3/4/5. DOT 5.1 is barely mentioned, but it's assumed that it has to meet all the performance requirements of DOT 5. By definition DOT 5 is silicone while DOT 5.1 is glycol that's inherently compatible with DOT 4 and DOT 3 fluids. If you're worried about there being some incompatibility because a little bit of the previous fluid is in there, don't worry about it. I remember once I provided a bottle of DOT 4 brake fluid for a shop to use, and when it wasn't enough they supplemented it with a bottle of a different brand of DOT 4. They said it's not really a problem since they'll mix just fine and the additive chemistries are pretty similar. The required viscosity of DOT 4 is lower than DOT 3. DOT 5's required viscosity is even lower. I believe a lot of the testing requirements are the same for all grades of brake fluid, although there are some tests (like the pH test) that can't

The other important thing is the color. Silicon brake fluid must be dyed purple. DOT 3/4/5.1 must be clear to amber. There was a non-compliant DOT 4 brake fluid that was blue (ATE Super Blue). Apparently some would alternate using that with an amber brake fluid to help with flushing. If it had blue brake fluid in there, it would be bled until it started coming out amber. If it had amber brake fluid it would be bled until it started coming out about the shade of blue as the blue brake fluid. You can't get that in the US any more because it doesn't meet the FMVSS 116 standard. Not sure about Canada though.
 
Originally Posted by Wolf359
The main difference between different DOT 3 products is the wet and dry boiling points. The higher the number the better. There are minimum levels that all DOT3 products have to meet so any DOT3 product will be fine, it's just that if you have a choice, get the one with the higher boiling point. DOT4 is even higher, but the price tends to be a bit more and if it's a beater, DOT3 will be fine. A quart is usually plenty to bleed the entire system even with an empty master cylinder, they don't typically hold that much fluid.

Some DOT 3 brake fluids have a higher dry boiling point than some DOT 4 fluids. But they have to meet wet boiling point requirements too.
 
Go to any auto parts store or Walmart(SuperTech) and buy 2 quarts of their house brand or name brand on sale. If you don't open the 2nd quart, return it.
 
DOT 3 mixed with DOT 3 from a different brand. Mix away. They may or may not be identical, but it won't matter as long as they're DOT 3. You can even mix DOT 4, or 5.1 into a system that calls for DOT 3.
 
Originally Posted by ST2008
Hi guys. I'm not very familiar with brake fluid so I have a noob question for you. Are all DOT3 brake fluid compatible? If the answer is yes, are all DOT3 the same quality? I need to bleed the whole brake system of my car. For this I need a great amount of brake fluid. A local auto parts store has brake fluid on sale this week. their brake fluid is three time cheaper than the dealer. But before buying their brake fluid, I want to make sure that there is no compatibility issues, different specifications or quality standards like in the realm of engine oil. thx


I bought a one gallon jug of DOT 3 from Canadian Tire last year, at the time it was the cheapest I could find. If you haven't done a brake fluid flush for a while you will immediately notice an improvement.
 
Status
Not open for further replies.
Back
Top