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Is there any advantage to DOT3 over DOT4? #4976553 01/11/19 10:18 PM
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littlehulkster Online Content OP
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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?


2015 Mazda3 I 2.0
Re: Is there any advantage to DOT3 over DOT4? [Re: littlehulkster] #4976568 01/11/19 10:34 PM
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Yes, use the DOT 4 smile

Re: Is there any advantage to DOT3 over DOT4? [Re: littlehulkster] #4976569 01/11/19 10:36 PM
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demarpaint Offline
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I'd use the DOT 4.


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Re: Is there any advantage to DOT3 over DOT4? [Re: littlehulkster] #4976597 01/11/19 11:16 PM
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DOT4 is superior.


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Re: Is there any advantage to DOT3 over DOT4? [Re: littlehulkster] #4976603 01/11/19 11:26 PM
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Wolf359 Offline
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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.

Re: Is there any advantage to DOT3 over DOT4? [Re: Wolf359] #4976605 01/11/19 11:31 PM
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littlehulkster Online Content OP
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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.


2015 Mazda3 I 2.0
Re: Is there any advantage to DOT3 over DOT4? [Re: littlehulkster] #4976623 01/12/19 12:05 AM
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Wolf359 Offline
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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.

Re: Is there any advantage to DOT3 over DOT4? [Re: littlehulkster] #4976676 01/12/19 03:33 AM
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They taste the same to me....


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Re: Is there any advantage to DOT3 over DOT4? [Re: littlehulkster] #4976811 01/12/19 09:42 AM
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Audios Offline
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DOT 3 is less likely to absorb water and can usually go longer in the system before changing. However 4 is the better fluid.


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Re: Is there any advantage to DOT3 over DOT4? [Re: Audios] #4976828 01/12/19 09:58 AM
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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?


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Re: Is there any advantage to DOT3 over DOT4? [Re: littlehulkster] #4976845 01/12/19 10:22 AM
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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.


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Re: Is there any advantage to DOT3 over DOT4? [Re: Dufus2] #4976854 01/12/19 10:30 AM
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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.


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Re: Is there any advantage to DOT3 over DOT4? [Re: spk2000] #4977211 01/12/19 05:35 PM
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Wolf359 Offline
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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.

Re: Is there any advantage to DOT3 over DOT4? [Re: littlehulkster] #4977266 01/12/19 06:46 PM
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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.

Re: Is there any advantage to DOT3 over DOT4? [Re: Wolf359] #4977279 01/12/19 07:00 PM
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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.


Plain, simple Garak.

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