DOT 4 or 5.1?

[rup5555555]

The manual says DOT 4 fluid for '05 ABS 12GS. Is there any advantage in using DOT 5.1? Thx

 

[MattW]

The manual says DOT 4 fluid for '05 ABS 12GS. Is there any advantage in using DOT 5.1? Thx

Reducing the weight of your wallet

 

[nedflanders]

The manual says DOT 4 fluid for '05 ABS 12GS. Is there any advantage in using DOT 5.1? Thx

From what I can remember DOT 4 is perfectly good for road use, I think DOT 5 was created for applications generating a lot of heat like racing to prevent the fluid boiling off. Only downside is the fluid needs changing quite regularly (like after every race) I bought a car with some in and the fluid had started to cystalize . one thing I have learn't though is stick to what a manufacturer says

 

[Whele]

The manual says DOT 4 fluid for '05 ABS 12GS. Is there any advantage in using DOT 5.1? Thx

I can assure you it will not make any difference, your still f***** when the servo fails

 

[MattW]

From what I can remember DOT 4 is perfectly good for road use, I think DOT 5 was created for applications generating a lot of heat like racing to prevent the fluid boiling off. Only downside is the fluid needs changing quite regularly (like after every race) I bought a car with some in and the fluid had started to cystalize . one thing I have learn't though is stick to what a manufacturer says

DOT5 and DOT5.1 are very different.

5 is a synthetic non-hygroscopic fluid

5.1 is a 'normal' fluid in that it's hygroscopic and eats paint etc

5 should not be mixed with either 5.1 or 4

 

[WindyChuffer]

So by that rationale DOT 5 fluid, not being hygroscopic, will never need changing then? After all, the main driver behind changing brake fluid is because normal fluid is hygroscopic and absorbs water.

Correct or tosh?

 

[alimey4u2]

This is from Mike Nixon an ex Honda mechanic, not all he says is accurate but this is about right...

http://www.motorcycleproject.com/motorcycle/text/cows-brakefluid.html

Me ? Using DOT 5 in my classic for 15 years without problems, we actually I find benefits but then lots of pros will say different. Although some of them are younger than said bike...

 

[MattW]

What I have read is that DOT5 should never be mixed with other brake fluid types. A change to DOT5 apparently requires a complete brake system clean out / renewal

However as this thread is about 5.1, I guess it doesn't matter.

 

[Dickieboy]

This is from Mike Nixon an ex Honda mechanic, not all he says is accurate but this is about right...

http://www.motorcycleproject.com/motorcycle/text/cows-brakefluid.html

Me ? Using DOT 5 in my classic for 15 years without problems, we actually I find benefits but then lots of pros will say different. Although some of them are younger than said bike...

He's a bit confusing in places.

"So now we have D.O.T. 3, 4, 5, and 5.1, with all but the 5 designation being glycol, while the 5 is silicone. "

 

[MattW]

He's a bit confusing in places.

"So now we have D.O.T. 3, 4, 5, and 5.1, with all but the 5 designation being glycol, while the 5 is silicone. "

I think for us mortals who aren't racing or starting off with new / clean brake systems, the general guidance is to stick to the manufacturers recommended DOT4. If you want to spend a bit more money, use 5.1 although you won't see any benefit (assuming you change the fluid at the recommended intervals). Stay away from 5.1 unless you're starting 'clean' and know what you're doing.

Once you throw painfully expensive ABS units into the equation, it's the manufacturers recommended DOT4 every time for me.

 

[alimey4u2]

Yes DOT 5 required a total strip & new rubbers if converted. However, it is a factory installation for most Hardly Ablesons...Nuff said really...

I use it in my garage queen because it is just that....

 

[Zigo]

Beware of DOT confusion!

Brake fluids DOT 4 and 5.1 are glycol based fluids with similiar properties.
DOT 4 has a dry boiling point of 230 deg C (as when it's new), wet boiling point is 155deg C (after approx 1 year of use).
DOT 5.1 has a dry boiling point of 260deg C, and wet boiling point of 185. It have slightly a better visocity than DOT 4, making it somewhat better in ABS systems in cold weather. Can be mixed with DOT 4, but is more expensive.
Be careful with the silicone based DOT 5 and don't confuse it with DOT 5.1. DOT 5 has a boiling point of 260deg C and don't absorb water, true, but the fluid contain a certain amount of air molecules, making it more compressable. This mean your brakes wil feel more spongy, not good. The DOT 5 is shunned by racing people. It's NOT mixable with glycol based brake fluids. If mixed, a cemical reaction will cause solid particles to form in the brake circuits. To change to DOT 5 the whole system have to be flushed with special cleaner. To be safe a complete dismantling should be performed on the brake pistons, master cylinder and ABS unit, and the parts should be lubricated with DOT 5 when assembling. Another point in disfavour of DOT 5 is that any water that ingress into the system will not be absorbed, but will seek to the lower parts of the system, like calipers, causing corrosion. DOT 5 is often preferred by vintage car ownerson cars that are stored for long periods indoor.
PHEW!

 

[alimey4u2]

Apologies if I added to the confusion...

 

[rup5555555]

Will DOT5.1 last longer than DOT 4? And how often should you change the fluid? Thx

 

[karlp]

Brake fluids DOT 4 and 5.1 are glycol based fluids with similiar properties.
DOT 4 has a dry boiling point of 230 deg C (as when it's new), wet boiling point is 155deg C (after approx 1 year of use).
DOT 5.1 has a dry boiling point of 260deg C, and wet boiling point of 185. It have slightly a better visocity than DOT 4, making it somewhat better in ABS systems in cold weather. Can be mixed with DOT 4, but is more expensive.
Be careful with the silicone based DOT 5 and don't confuse it with DOT 5.1. DOT 5 has a boiling point of 260deg C and don't absorb water, true, but the fluid contain a certain amount of air molecules, making it more compressable. This mean your brakes wil feel more spongy, not good. The DOT 5 is shunned by racing people. It's NOT mixable with glycol based brake fluids. If mixed, a cemical reaction will cause solid particles to form in the brake circuits. To change to DOT 5 the whole system have to be flushed with special cleaner. To be safe a complete dismantling should be performed on the brake pistons, master cylinder and ABS unit, and the parts should be lubricated with DOT 5 when assembling. Another point in disfavour of DOT 5 is that any water that ingress into the system will not be absorbed, but will seek to the lower parts of the system, like calipers, causing corrosion. DOT 5 is often preferred by vintage car ownerson cars that are stored for long periods indoor.
PHEW!

Absolutely spot on.

Amazing how much rubbish has been stated in some of the earlier postings.
Why do people some profess to know everything when they know nothing.

 

[Daffy]

As a general rule of thumb, don't mix fluids and use exactly whats on the cap.

You will find that seals can be affected by the wrong fluid, try putting brake fluid in your clutch m/cyl (pentosin), ones mineral and the others vegetable and the seals do not like it.

I am not talking BMW experience here but have some experience in this area as castrol misquoted a fluid for a truck clutch system with extreme results.

 

[Zigo]

Will DOT5.1 last longer than DOT 4? And how often should you change the fluid? Thx

The difference between DOT 4 and 5.1 is basically the boiling point level. These glycol based fluids will generally absorb more than 3% water a year, so follow BMW's recommendation for changing or every two years. My personal opinion is that unless you are live on the racetrack or in the Alps, DOT 4, as also recommended by BMW, is more than good enough and also cost less

 

[Andy B]

Ditto

Phone your dealer and they'll tell you DOT 4.

Find something more important in life worry about!!