DOT 5 vs 5.1? What are you using?

[Zeus51]

Is everyone using DOT 5? Or are you using 5.1 brake fluid? I'm looking for your opinions on type and brand? And..... GO!

 

[jbayer]

You do realize DOT 5.1 is Glycol based (same as DOT 3/4), and IS NOT compatible with DOT 5.

 

[MarkM]

Below may help:

[FONT=&quot][FONT=Arial,Helvetica]DOT3[/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] DOT3 brake fluid is the "conventional" brake fluid used in most vehicles.[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] Advantages:[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] DOT3 fluid is inexpensive, and available at most gas stations, department stores, and any auto parts store.[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] Disadvantages:[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] DOT3 fluid eats paint![/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] DOT3 fluid absorbs water very readily. (This is often referred to as being hydroscopic.) As such, once a[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] container of DOT3 has been opened, it should not be stored for periods much longer than a week before use.[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] Since DOT3 fluid absorbs water, any moisture absorbed by the fluid can encourage corrosion in the brake lines[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] and cylinders.[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica]DOT4[/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] DOT4 brake fluid is the brake fluid suggested for use in some late model cars.[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] Advantages:[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] DOT4 fluid is available at most auto parts stores, and at some (but not all) gas stations or department stores.[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] DOT4 fluid does not absorb water as readily as DOT3 fluid.[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] DOT4 fluid has a higher boiling point than DOT3 fluid, making it more suitable for high performance applications[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] where the brake systems are expected to get hot.[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] Disadvantages:[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] DOT4 fluid eats paint! Small leaks around the master cylinder will eventually dissolve away the paint on your[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] bodywork in the general vicinity of the leak, and then give rust a chance to attack the body of your car![/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] DOT4 fluid is generally about 50% more expensive than DOT3 fluid.[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] Since DOT4 fluid still absorbs some water, any moisture absorbed by the fluid can encourage corrosion in the[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] brake lines and cylinders.[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica]DOT5[/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] DOT5 brake fluid is also known as "silicone" brake fluid.[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] Advantages:[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] DOT5 doesn't eat paint.[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] DOT5 does not absorb water and may be useful where water absorption is a problem.[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] DOT5 is compatible with all rubber formulations. (See more on this under disadvantages, below.)[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] Disadvantages:[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] DOT5 does NOT mix with DOT3, DOT4 or DOT5.1. Most reported problems with DOT5 are probably due to some[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] degree of mixing with other fluid types. The best way to convert to DOT5 is to totally rebuild the hydraulic[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] system.[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] Reports of DOT5 causing premature failure of rubber brake parts were more common with early DOT5[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] formulations. This is thought to be due to improper addition of swelling agents and has been fixed in recent[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] formulations.[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] Since DOT5 does not absorb water, any moisture in the hydraulic system will "puddle" in one place. This can[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] cause localized corrosion in the hydraulics.[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] Careful bleeding is required to get all of the air out of the system. Small bubbles can form in the fluid that will form[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] large bubbles over time. It may be necessary to do a series of bleeds.[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] DOT5 is slightly compressible (giving a very slightly soft pedal), and has a lower boiling point than DOT4.[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] DOT5 is about twice as expensive as DOT4 fluid. It is also difficult to find, generally only available at selected[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] auto parts stores.[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica]DOT5.1[/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] DOT5.1 is a relatively new brake fluid that is causing no end of confusion amongst mechanics. The DOT could avoid a[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] lot of confusion by giving this new fluid a different designation. The 5.1 designation could lead one to believe that it's a[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] modification of silicone-based DOT 5 brake fluid. Calling it 4.1 or 6 might have been more appropriate since it's a[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] glycol-based fluid like the DOT 3 and 4 types, not silicone-based like DOT 5 fluid.[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] As far as the basic behavior of 5.1 fluids, they are much like "high performance" DOT4 fluids, rather than traditional[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] DOT5 brake fluids.[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] Advantages:[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] DOT5.1 provides superior performance over the other brake fluids discussed here. It has a higher boiling point,[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] either dry or wet, than DOT 3 or 4. In fact, its dry boiling point (about 275 degrees C) is almost as high as racing[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] fluid (about 300 degrees C) and 5.1's wet boiling point (about 175 to 200 degrees C) is naturally much higher[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] than racing's (about 145 C).[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] DOT5.1 is said to be compatible with all rubber formulations.[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] Disadvantages:[/SIZE][/FONT][/FONT]
[FONT=&quot][FONT=Arial,Helvetica][SIZE=-1] DOT5.1 fluids (and Spectro's Supreme DOT4) are non-silicone fluids and will absorb water.[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] DOT5.1 fluids, like DOT3 & DOT4 will eat paint.[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] DOT 5.1 fluids are difficult to find for sale, typically at very few auto parts stores, mostly limited to "speed shops."[/SIZE][/FONT]
[FONT=Arial,Helvetica][SIZE=-1] DOT 5.1 will be more expensive than DOT3 or DOT4, and more difficult to find.[/SIZE][/FONT][/FONT]

 

[Zeus51]

Thanks guys! Yes sir. I am aware of their incompatibilities. I have to do a complete new brake system on my M1008 due to multiple leaks and was wondering what popular opinion was on the two different fluids. I assume most people are using DOT 5 silicone? But I'm also wondering if given the opportunity, have they or would they switch to 5.1 or do most people feel that 5.0 is so far superior that there's no sense in switching. I would love to hear some thoughts?

 

[The FLU farm]

I think DOT 5.1 could be warranted if, for example, you tend to come out of turn 8a at Laguna Seca way too hot.
Or, more realistically for an M1008 perhaps, frequently tow in excess of 10,000 lbs., without trailer brakes.

 

[Drock]

I use ("Stainless steel brakes") DOT5 fluid. It's cheaper than Napa brand, but you have to order it.

 

[M1911A1]

Just changed mine with some fresh very expensive Dot 5.


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[DREDnot]

Is there any way to tell if your newly purchased CUCV still has the original DOT5, or was switched over to DOT3 by someone previously?
I don't want to add DOT5 and have a mess if DOT 3 was in there.

 

[Migginsbros]

We prefer DOT 5 silicon in our "old" vehicles.
It´s our choice in not often used cars & bikes.
It´s used for long term storage at the military.
It´s used by Harley Davidson (doesn´t eat paint)about 30 years till Anti lock brakes became standart.

Dot 3/4/5.1 should be changed after 2 years because the water absorbing (surronding/ambient air) problem.

DOT 5 silicone is not recommended for Anti lock brake systems.

 

[Migginsbros]

Is there any way to tell if your newly purchased CUCV still has the original DOT5, or was switched over to DOT3 by someone previously?
I don't want to add DOT5 and have a mess if DOT 3 was in there.

DOT 5 silicon is slippery between your fingers.
Dot 3/4/5.1 is not (dulled?)
If you have an electronic brake fluid tester (will measure the amount of water) the tester will show something (on scale or LED lights) with 3/4/5.1
and nothing if DOT5 silicon is in your master cyl. reservoir.

 

[doghead]

Mix a bit of your fluid with a bit of water in a small container.

Stir it up and wait a few minutes.

If it separates, you have silicone.

If it stays mixed and cloudy, you have dot3

There are dozes of threads explaining this, and I think there is even a sticky.

 

[snowtrac nome]

Also remember on the glycol based fluids, the more water absorbed in the system the lower the boiling point.

 

[DREDnot]

DOT 5 silicon is slippery between your fingers.
Dot 3/4/5.1 is not (dulled?)
If you have an electronic brake fluid tester (will measure the amount of water) the tester will show something (on scale or LED lights) with 3/4/5.1
and nothing if DOT5 silicon is in your master cyl. reservoir.

Thanks for that info. Just what I needed to know.

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[sneekyeye]

When I bought my truck, I flushed the brake fluid. The previous owner didn't know what was in it and it looked pretty funky. So I used dot4 for the simple reason that I still have something like forty more quarts left of the stuff sealed.

 

[Drock]

Original DOT 5 was yellow, All the new stuff is purple.

 

[jbayer]

Original DOT 5 was yellow, All the new stuff is purple.

I'm pretty sure it's always been purple right out of the bottle. (At least for the last 35 years that I know of) It does turn yellow with age when it's in a vehicle though.

 

[Zeus51]

Ok. Great! This is all great info. And I appreciate all of the experienced opinions and knowledge. So in the pic below, this is my existing master cylinder. Are the color differences proof of mixed fluid? Or is there another reason it would change color?

 

[porkysplace]

Ok. Great! This is all great info. And I appreciate all of the experienced opinions and knowledge. So in the pic below, this is my existing master cylinder. Are the color differences proof of mixed fluid? Or is there another reason it would change color?

View attachment 703462

Follow the instructions in this thread and test it , it hard to tell from a picture.
But either way it may be time for you to flush and refill your system.
[h=1]Brake fluid -how to tell which kind you have DOT 3 or DOT 5[/h]

 

[Zeus51]

Follow the instructions in this thread and test it , it hard to tell from a picture.
But either way it may be time for you to flush and refill your system.
Brake fluid -how to tell which kind you have DOT 3 or DOT 5

Wow! Thanks. I thought I looked in the sticky's for something like that link. If it's not one, it should be!

 

[joshuak]

Ok. Great! This is all great info. And I appreciate all of the experienced opinions and knowledge. So in the pic below, this is my existing master cylinder. Are the color differences proof of mixed fluid? Or is there another reason it would change color?

I may be mistaken but another reason for color change could be hoses disintegrating from the inside out, as well as seals in your MC.

I flushed my system out two years ago and removed this:



Flushed again last week (2 year old fluid from MC shown on right), replaced hoses, calipers and MC this time, and new fluid from purging on left.