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Brake Fluid - Dot 4 or Dot 5?

kb3

kb3

Well-Known Member
The more I read about Dot 4 and Dot 5, the more confused I get. I know that Dot 5 will not hurt the paint, but it appears to have other negatives Dot 4 doesn't have. What have others used and can someone sway me in one direction?
 
I've used DOT5, and am very pleased, especially with the friendliness with paint. The biggest drawback that I've read is that it has a lower boiling point (important if you're doing serious tracktime). The only other thing to watch for is to not shake the bottle before use: it has a tendency to keep small bubbles entrained for a long time.

I bleed the brakes once every two years just to keep the fluid fresh.
 
I don't understand the desire or need for DOT 5 fluid. I bleed the brakes before every track day, so sometimes they get bled 6 or 7 times a year and sometimes just once. I've never had a problem with brake fluid and paint.

I use DOT 4 and have never had a problem.
 
i can't speak for the performance aspect, but i went with DOT 5 primarily due to the fact i installed all new brakes, lines, master cylinder, etc. in addition i was adding in a line lock and proportioning valve so i had to make a lot of new flares (i went with all stainless).

also everything has been freshly painted (undercarriage as well).

i had a lot of leaks everywhere. it was nice not worrying about any paint getting lifted.

the pedal doesn't have any spongy feeling.

maybe once i get some miles on it and feel that everything is good for the long haul, i'll flush it out.
 
DOT 5 is not hygroscopic meaning it doesn't absorb water like DOT 3 does. When this water migrates down into the calipers, the heat created in performance apps will boil the water leaving you with crappy stopping ability.

DOT 5 cannot be mixed or added to DOT 3 of 4. If you try DOT 5 and don't like it, you'll have to replace your entire brake system.

DOT has more space for air between its molecules making it more compressible and sometimes resulting in a spongy pedal.

DOT 5 doesn't eat paint.

I would only use DOT 5 for a show car that gets rolled on and off a trailer. If you want to drive the thing then stick with DOT 3 and learn how to bleed brakes without making a mess.
 
"Shaun" said:
DOT 5 is not hygroscopic meaning it doesn't absorb water like DOT 3 does. When this water migrates down into the calipers, the heat created in performance apps will boil the water leaving you with crappy stopping ability.

DOT 5 cannot be mixed or added to DOT 3 of 4. If you try DOT 5 and don't like it, you'll have to replace your entire brake system.

DOT has more space for air between its molecules making it more compressible and sometimes resulting in a spongy pedal.

DOT 5 doesn't eat paint.

I would only use DOT 5 for a show car that gets rolled on and off a trailer. If you want to drive the thing then stick with DOT 3 and learn how to bleed brakes without making a mess.
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just curious, have you tried using DOT 5 or is this information that you've read?
 
I too am interested in Dot5 and primarily for the paint friendly aspect. Like Demon, I have all new stainless lines and new discs all the way around. With respect to street driven weekend car, what exactly isn't there to like about DOT5?
 
"miketyler" said:
I too am interested in Dot5 and primarily for the paint friendly aspect. Like Demon, I have all new stainless lines and new discs all the way around. With respect to street driven weekend car, what exactly isn't there to like about DOT5?
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The only (slightly) negative aspect is that DOT5 can be hard to find in the parts stores.
 
i did a lot of internet research before making the decision. i read a number of comments like shaun wrote. however, i had the feeling many of those comments were from people repeating what they read instead of reporting their actually personal experiences.

i'm certain performance wise there is really a loss with DOT 5 or the bottle itself wouldn't have the warnings and our new cars would use it.

i wonder if the reason daily driven cars don't use it is because they seldom get bled, flushed and experience all environments. the car i drive everyday is now 18 years old and i've never bled the brakes. could DOT 5 and that brake system stand up to that abuse?

my mustang is and will be in a climate controlled environment 99% of it's life. i won't be hammering corners or braking hard repeatedly. add in the fact that i'll probably bleed the brakes every few years gave me a feeling it would be ok with the DOT 5.

a friend of mine drives an old challenger with DOT 5. he didn't notice any difference when switching. but again, he's pretty easy on the car.

i would love to hear anyone's negative personal experiences with DOT 5. personally, at this point i could care less about the stereotypically negatives of DOT 5 because i've read those issues when searching with Google.

hopefully others will respond and won't be scared to state they use DOT 5. it would be nice if information like the cars use, driving style and environmental conditions were indicated.
 
"buckeyedemon" said:
just curious, have you tried using DOT 5 or is this information that you've read?
Click to expand...

I don't need to try it to find out the negatives. If you say new cars come with it perhaps thats why alot of them have brake bleeding on the maintenance schedule.

For anyone with $25 that wants to learn more about brakes I recommend reading 'High Performance Brake Systems' by James Walker who knows more about brake systems then most of us combined. Chapter 6 talks alot about fluid.

You have to consider the source when reading internet forums. My Dad would have you believe that everything he reads online is true though! Drives me crazy.
 
DOT 5 http://en.wikipedia.org/wiki/DOT_5

Basically, DOT 5 does not entrain as much water, but it does absorb a little air. Enough to give a spongy pedal (and this is why you don't shake the bottle).

There is a DOT 5.1, which is not related to DOT 5 http://en.wikipedia.org/wiki/DOT_5.1

It's more closely related to DOT 3 ( http://en.wikipedia.org/wiki/DOT_3 ) and DOT 4 ( http://en.wikipedia.org/wiki/DOT_4 ) .

Note that DOT 4 has apparently superseded DOT 3, at least for the most part. However, I've heard something about DOT 4 absorbing water a little faster than DOT 3.

It's probably best to shop for either 3 or 4 with higher boiling points, particularly the wet boiling point if your car is driven frequently/daily.

I've been using Castrol GTLMA in all of my cars (it meets the 311F wet boiling spec for DOT 4 and typically tests dry at above 500F.

I wouldn't use DOT 5 in anything except a museum car or maybe an always-trailered show car.


Norm
 
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