Is there any advantage to DOT3 over DOT4?

[littlehulkster]

I need a brake flush in my 2015 Mazda3, and while the manual specifies DOT3, I have a large unopened bottle of DOT4 I had bought for a future job on my old car. I understand that DOT4 can be used in any application where DOT3 is specified without harm, but I was also thinking that since this car is a 2015, Mazda could have specced it for DOT4 in the manual but didn't, and DOT4 is not even mentioned. However, it seems that DOT4 is a flatly superior product.

Is there some sort of advantage to DOT3 over DOT4 that I'm not aware of, or was the DOT3 spec just a matter of cost? I guess to rephrase the question, I know I CAN use DOT4, but SHOULD I?

 

[slacktide_bitog]

Yes, use the DOT 4

 

[demarpaint]

I'd use the DOT 4.

 

[FordBroncoVWJeta]

DOT4 is superior.

 

[Wolf359]

Yes, the only real difference is the cost, Dot 4 can be about double or so the price of Dot 3. Only reason for Dot 3 would be that the car isn't high powered and the brakes won't really be taxed so there's no need for the higher boiling points of Dot 4. But if you already have it, go ahead and use it.

 

[littlehulkster]

Originally Posted by Wolf359
Yes, the only real difference is the cost, Dot 4 can be about double or so the price of Dot 3. Only reason for Dot 3 would be that the car isn't high powered and the brakes won't really be taxed so there's no need for the higher boiling points of Dot 4. But if you already have it, go ahead and use it.


I guess I have to wonder why DOT3 is even sold anymore, then. Sure, 4 costs more, but brake fluid is cheap overall. The cost of using DOT4 over 3 may be 2x, but 2x 5 is only 10.

 

[Wolf359]

Well the manufacturers watch every penny. Some recalls are caused by penny pincher that shave a few cents off the cost of a part. If you save $5 extra per car and sell 100k, that's a $500k savings. A few dollars here and there can add up to millions without raising the price.

 

[HorseThief]

They taste the same to me....

 

[Audios]

DOT 3 is less likely to absorb water and can usually go longer in the system before changing. However 4 is the better fluid.

 

[spk2000]

Originally Posted by Audios
DOT 3 is less likely to absorb water and can usually go longer in the system before changing. However 4 is the better fluid.


Have heard this more than once but never saw anything that proves it is true and not just rumor. Anyone got some studies or evidence?

 

[Dufus2]

I used DOT 4 from Napa and it seems to be a little thicker, in very cold weather DOT 4 may be slower to respond. I just use the Walmart SuperTech DOT 3 brake fluid (paid $5 for a quart) and change it out every 2-3 years depending upon the condition. I just bought a brake fluid tester pen and my old fluid tested at 1-2% moisture after at least two years.

 

[mightymousetech]

Originally Posted by Dufus2
I used DOT 4 from Napa and it seems to be a little thicker, in very cold weather DOT 4 may be slower to respond. I just use the Walmart SuperTech DOT 3 brake fluid (paid $5 for a quart) and change it out every 2-3 years depending upon the condition. I just bought a brake fluid tester pen and my old fluid tested at 1-2% moisture after at least two years.


There is DOT 4 low viscosity. It is what BMWs call for.

 

[Wolf359]

Originally Posted by spk2000
Originally Posted by Audios
DOT 3 is less likely to absorb water and can usually go longer in the system before changing. However 4 is the better fluid.


Have heard this more than once but never saw anything that proves it is true and not just rumor. Anyone got some studies or evidence?


I heard that as well, further research seems to show that Dot 4 actually absorbs less water than even Dot 3 so that bit isn't even true. The more frequent flush recommendation may just be a good reason for some dealer to get the car in for maintenance.

 

[nobb]

If you're changing your fluid often, the dry boiling point is more important. If you're not changing your fluid often, then the wet boiling point is more important. There's some DOT 3 fluids (like Ford PM-1-C) that actually outperform the DOT 4 standard for dry boiling point, but falls short in the wet boiling point.

 

[Garak]

Originally Posted by Wolf359
I heard that as well, further research seems to show that Dot 4 actually absorbs less water than even Dot 3 so that bit isn't even true. The more frequent flush recommendation may just be a good reason for some dealer to get the car in for maintenance.

Something like Castrol LMA DOT 4 certainly markets based upon that aspect. Whether that's true for other DOT 4 varieties, I have no idea.

 

[y_p_w]

DOT3 is a standard and not necessarily a description of the fluid. All DOT4 fluids meet DOT3 standards. By the same token, DOT5.1 fluids (I've got some old Motul and some Wagner) also meet DOT3 standards.

I have heard of some "super heavy duty" DOT3 fluid that has an extremely high dry boiling temperature and theoretically are excellent for racing as long as it's changed before a race. I guess the boiling temp rapidly drops with moisture, but it's pretty cheap to replace. I can't see changing brake fluid that often for a daily driver though. I'd recommend 5.1.

 

[blupupher]

Considering most vehicles never get a brake fluid change, use whatever if your changing it.

I personally use the cheap store brand DOT 3/4 labeled fluids (no idea on actual specs) since I am changing it every few years.
I have debated doing DOT 5.1 on my motorcycle just because, but just can;t make myself buy some.

 

[pezzy669]

DOT 4 only seems to be a German car thing from what I have gathered - with VW/Audi and MB both recommending every 2 year changes I don't see the benefit of the "better" fluid but I digress.

When I did my own bleeds on my '03 Golf TDI I used the DOT 4 ATE fluid that was tinted blue and alternated with the DOT 4 ATE amber fluid, made it super easy to bleed as you could visually tell once all the old fluid was flushed out with the change in color.

 

[Garak]

The G37 calls for DOT 3, yet, oddly enough, the Infiniti dealer only had DOT 4 on the shelves, and it was a Nissan branded product. I wasn't considering buying, but it just did stand out. I have no reason to buy any other brake fluid anywhere, DOT 3 or 4, given the small amount I pay for Castrol LMA.

 

[y_p_w]

Originally Posted by Garak
The G37 calls for DOT 3, yet, oddly enough, the Infiniti dealer only had DOT 4 on the shelves, and it was a Nissan branded product. I wasn't considering buying, but it just did stand out. I have no reason to buy any other brake fluid anywhere, DOT 3 or 4, given the small amount I pay for Castrol LMA.

Understood since it's labeled as such. However, DOT 3 is a specification and not necessarily a product. Fluid meeting DOT 4/5.1 specs could comceivbly be labeled as DOT 3. There was an outlier when Valvolinw has its SynPower brake fluid. It was marketed as exceeding DOT 4 by a good margin, but not quite at DOT 5.1. The wet boiling point was a little bit lower.

I've never seen a warning to not use DOT 4/5.1 where DOT 3 is specified. Only warnings against DOT 5 silicone.