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Thread: Dot 3 brake fluid okay to use?

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    Senior Member fc321's Avatar
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    Dot 3 brake fluid okay to use?

    Is Dot 3 brake fluid okay to use instead of Dot 4? The price difference in my city is 4x more expensive for Dot 4


    2015 Mirage DE 5 speed Manual - 30k miles

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        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 44.9 mpg (US) ... 19.1 km/L ... 5.2 L/100 km ... 53.9 mpg (Imp)


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    Quote Originally Posted by fc321 View Post
    Is Dot 3 brake fluid okay to use instead of Dot 4? The price difference in my city is 4x more expensive for Dot 4
    The FSM says either DOT3 or DOT4.

    BTW, In these parts, I haven't seen DOT3 in years...

    If you don't have a FSM (Factory Service Manual), I would recommend you get one! Where from? Do a little search in the forum.
    Last edited by foama; 02-02-2019 at 07:16 PM.

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    Still Plays With Cars Loren's Avatar
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    DOT 3 is "okay", but look at the "wet boiling point". DOT 4 is always going to have better specs.

    Brake fluid is hygroscopic, that means it absorbs water.

    Dry boiling point is the temperature at which the fluid will boil with zero moisture present in it, generally this is as it comes out of the freshly opened container.

    Wet boiling point is the temperature at which water-saturated fluid will boil, and it is considerably LOWER. It normally takes 2-3 years for brake fluid to reach this point, which is why you should change your brake fluid every couple or three years.

    When brake fluid boils, it releases bubbles of air into the braking system, which is bad. Brake fluid does not compress. But, the bubbles DO compress, and can make your brake system very ineffective. (spongy, soft pedal)

    This can be the difference between being able to make ONE good stop from 60-70 mph without boiling your fluid, and being able to make TWO or THREE good stops from 60-70 mph without boiling your fluid. Once it's boiled, you've got air in the system, and it's a problem that doesn't fix itself. The only solution is to bleed the brakes to remove the air.

    Most people hardly ever brake hard enough to worry about it. But, if you ever go drive in the mountains and have to use your brakes a lot... think about your brake fluid.
    Simplify and add lightness.

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    Senior Member fc321's Avatar
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    Thanks for this detailed explanation. I was attracted to buying a gallon of the Dot 3 because my Moms car, my sisters car and also my roomate they all have cars that call for Dot 3 fluid so I thought I could buy the gallon and then service all the cars together

    But I think I will just get Dot 4 for the Mirage because already the brakes are not very impressive. I almost crashed a few days ago when I had to SLAM the brakes after a dumb-bell just stopped without rhyme or reason ahead of me and if it where not for the generous amount of following distance (3-4 seconds) that I leave I would have rear-ended that bozo for certain.

    So im not sure what fluid was put in from the factory but the braking on this car is the worst of any car I have ever owned. In fact I recall a thread on this same forum of a guy that rear ended somebody and then Loren had "issued a correction" to the guy and the man got offended about it.

    Not sure if Loren remembers that old thread but I can probably pull it up because I just read that maybe a month ago
    2015 Mirage DE 5 speed Manual - 30k miles

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 44.9 mpg (US) ... 19.1 km/L ... 5.2 L/100 km ... 53.9 mpg (Imp)


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    Still Plays With Cars Loren's Avatar
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    I remember. And kudos to you for keeping adequate space, and thus not becoming a statistic.

    But, changing your brake fluid is NOT going to make your car brake any better unless you've already boiled the fluid and have bubbles in your system. If the pedal isn't spongy, then fresh brake fluid isn't going to help the car stop any quicker.

    If you want the car to stop quicker, you need better TIRES. Period.

    Brake fluid either works or it doesn't. As long as you're not cooking it, pretty much anything will work just fine, and work EXACTLY the same way.

    You could fit better brake pads and get better pad "feel" with a pad that bites quicker and harder. But, ultimately, even with the pads you have... you might have to apply more pedal pressure, but you have enough brake power to lock up the tires. ABS keeps the tires from fully locking up, but the tires are what is limiting the stopping distance of the car. Grippier tires stop better. The antithesis of economy tires. Everything is a compromise.

    You could even update to the larger 2017+ brakes, and that would make the brakes "feel" a little better, too. But, still... it's the tires that actually stop the car.
    Simplify and add lightness.

  6. The Following 4 Users Say Thank You to Loren For This Useful Post:

    A-Aron (02-03-2019),Adam - UK (02-04-2019),fc321 (02-03-2019),poorman1 (02-03-2019)

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    +1 and amen to that statement...
    Once the brakes can lock up the tires,, and abs kicks in.. how can the brakes do anything more.. in street use that is

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    fc321 (02-03-2019)

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    Senior Member fc321's Avatar
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    Quote Originally Posted by Loren View Post
    I remember. And kudos to you for keeping adequate space, and thus not becoming a statistic.

    But, changing your brake fluid is NOT going to make your car brake any better unless you've already boiled the fluid and have bubbles in your system. If the pedal isn't spongy, then fresh brake fluid isn't going to help the car stop any quicker.

    If you want the car to stop quicker, you need better TIRES. Period.

    Brake fluid either works or it doesn't. As long as you're not cooking it, pretty much anything will work just fine, and work EXACTLY the same way.

    You could fit better brake pads and get better pad "feel" with a pad that bites quicker and harder. But, ultimately, even with the pads you have... you might have to apply more pedal pressure, but you have enough brake power to lock up the tires. ABS keeps the tires from fully locking up, but the tires are what is limiting the stopping distance of the car. Grippier tires stop better. The antithesis of economy tires. Everything is a compromise.

    You could even update to the larger 2017+ brakes, and that would make the brakes "feel" a little better, too. But, still... it's the tires that actually stop the car.
    Oh, wow.

    I did not know that, I thought I just had to use a transfer pump to empty the reservoir and put fresh fluid inside.

    Ok. So you think there is not much value in only changing the fluid that is in the reservoir?
    2015 Mirage DE 5 speed Manual - 30k miles

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage DE 1.2 manual: 44.9 mpg (US) ... 19.1 km/L ... 5.2 L/100 km ... 53.9 mpg (Imp)


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    Senior Member Adam - UK's Avatar
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    what brand of TIRES are you using

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    fc321 (01-13-2022)

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    Still Plays With Cars Loren's Avatar
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    Quote Originally Posted by fc321 View Post
    Oh, wow.

    I did not know that, I thought I just had to use a transfer pump to empty the reservoir and put fresh fluid inside.

    Ok. So you think there is not much value in only changing the fluid that is in the reservoir?
    There is almost zero value in just replacing what's in the reservoir without flushing the whole system.
    Simplify and add lightness.

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    fc321 (01-13-2022)

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    Quote Originally Posted by Adam - UK View Post
    what brand of TIRES are you using
    In summer CONTINENTAL Eco Contact. Good grip, best for highway and lasts very long, but no good for winter.
    In Winter SAVA (cheap).


    Btw: Changing brake fluid every two years is standard procedure in Europe at the yearly dealer service.
    The way I drive, its not so much the boiling point as focus of concern, but rather the system rusting from the inside if it has too high water content.


    Last edited by foama; 02-04-2019 at 01:13 PM.

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