DOT3 or DOT4

[Decembermouse]

The only place I can find in town that sells brake fluid doesn't have DOT4 but they have DOT3. The guy says they're compatible but DOT3 boils at a slightly lower temperature. Is it ok for me to use this in the front brake? I know the thing says DOT4, but is it really necessary?

[freewheelers]

It depends on how hard you are on the brakes ... any reputable auto supply store should have it ... also walmart

[Neil Claydon]

Not something I would want to do, I have no problem getting the stock front brake to fade using dot 4.

Neil. ?

[pjk]

If you manage to boil your brake fluid your brakes stop working

[Wayward Son]

same stuff.

[Noble]

Pretty much the same stuff. Fully compatible. Where do you live that you can't buy DOT 4?

Neil - when you say fade the brakes, that is not really the same as boiling the fluid. Fade due to heat, the brakes start to feel greasy. Boil the fluid and the lever comes to the grip with no or little pressure in the system. If you are boiling the brake fluid, it needs to be changed (old fluid gets wet and boils sooner) and possibly up-grade to a better fluid: DOT 5.1 or a special high temp racing fluid.

[faffer]

They're compatible but a mixture of DOT3 and DOT4 has an even lower boiling temperature than plain DOT3.

[Noble]

You know, over the years DOT 3 vs DOT 4 has been discussed many times and every once in a while a new statement is made. Like DOT 4 attracts moisture less then DOT 3; and mix DOT 3 and 4 and it boils lower temp then either one. I'm not saying either statement is not true, but when I ask for supporting documentation it has never been offered. I really would like to know. Is there any supporting data for either of the above statements? Other than a small difference in boiling point is there anything superior about DOT 4?

[Neil Claydon]

Neil - when you say fade the brakes, that is not really the same as boiling the fluid. Fade due to heat, the brakes start to feel greasy. Boil the fluid and the lever comes to the grip with no or little pressure in the system. If you are boiling the brake fluid, it needs to be changed (old fluid gets wet and boils sooner) and possibly up-grade to a better fluid: DOT 5.1 or a special high temp racing fluid.

I am fully aware of the difference Noble, and yes lever to the bar,no brakes and hose was hot.

It happened within a week of getting the DRZ, and before I changed the fluid.

Neil. ?

PS: that didn't come out right Noble, I am not criticising you or your post

[robklx400]

3 or 4 it's such a small amount of fluid, just replace the full amount. I use 5.1 ever since I got SS lines.

[Decembermouse]

Sweet, good info. Basically, as long as I'm not racing the thing, I should be good to go with DOT3?

...btw, wouldn't a mixture of DOT3 and DOT4 still not have as high a boiling temp as pure DOT4? If you do a 50/50 ratio of both, I'd expect the boiling point of the resulting solution to be halfway in-between DOT3 and DOT4. And if you have enough of both to mix them, why would you even want to mix if you could use just DOT4?

DOT3 boils at 401 deg. F

DOT4 boils at 446 deg. F

(this is assuming they haven't absorbed any water apparently)

[Noble]

It is not uncommon for mixtures to exhibit characteristics different than either of the components. In metals it is called a low melting point eutectic. For example lead/tin solder melts at a lower temp then pure lead or pure tin. So it is certainly possible that a mixture of DOT 3 and DOT 4 has a boiling point less then DOT 3. But I would like to have some conformation if it is in fact true. I have never worried about it before and have mixed the 2 without concern. Perhaps I have been in error.

[Plane Dr]

Some seals and o rings can break down depending on type, as well. Not typically a problem but worth noting. Also I do believe DOT 4 is typically easier on paint (finishes) when spilled

[Decembermouse]

I agree with the solutions having different properties than simply those of their components, but lead and tin for instance are completely different elements, whereas DOT3 and DOT4 are both polyethylene glycol-based fluids (unlike DOT5, silicon) so I'm assuming, while there may be a different amount of buffer and such to compensate for the two different polyethylene glycol concentrations, and buffers and stabilizers are usually just benign substances that don't have a huge effect on the real properties of the 'active ingredient', if you will. For instance in toothpaste, the main component is humectant (like hydrated silica, also hygroscopic like p.e.g.!)but there are slightly varying concentrations of sodium fluoride or sodium monofluorophosphate. Much like (seemingly) there are just different concentrations of p.e.g. in DOT3 vs. DOT4.

This sound right?

[blt]

I agree with the solutions having different properties than simply those of their components, but lead and tin for instance are completely different elements, whereas DOT3 and DOT4 are both polyethylene glycol-based fluids (unlike DOT5, silicon) so I'm assuming, while there may be a different amount of buffer and such to compensate for the two different polyethylene glycol concentrations, and buffers and stabilizers are usually just benign substances that don't have a huge effect on the real properties of the 'active ingredient', if you will. For instance in toothpaste, the main component is humectant (like hydrated silica, also hygroscopic like p.e.g.!)but there are slightly varying concentrations of sodium fluoride or sodium monofluorophosphate. Much like (seemingly) there are just different concentrations of p.e.g. in DOT3 vs. DOT4.

This sound right?

Sounds like a hybrid oil thread, technically speaking.

[blt]

Actually I've mistaken,,,

Peanut oil would probably would be superior in this particular application due to it's higher smoking point

[Decembermouse]

Lol... nice.

[Noble]

OK, so now we have another claim for DOT 4. Easier on paint. I want to keep an open mind here but claims are just opinions until some kind of evidence can be provided.

DOT 4 absorbs less water?

DOT 3 and DOT 4 mix OK but will have a lower boiling point than either 3 or 4?

DOT 4 is easier on paint?

My skepticism is working over time. Is any of it true?

[crf250guy]

OK, so now we have another claim for DOT 4. Easier on paint. I want to keep an open mind here but claims are just opinions until some kind of evidence can be provided.

DOT 4 absorbs less water?

DOT 3 and DOT 4 mix OK but will have a lower boiling point than either 3 or 4?

DOT 4 is easier on paint?

My skepticism is working over time. Is any of it true?

This topic sparked an interest for me. I have spent some time researching it, and here are some links from what I consider to be reliable sources.

Info on differant types:

http://www.afcoracing.com/tech_pages/fluid.shtml

Info on mixing Dot 3 with Dot 4:

http://www.xs11.com/tips/maintenance/maint1.shtml

Advantages of higher DOT ratings:

http://www.ducatimonster.org/faq/faq_brake_fluid.html

It seems that the first two statements can be verfied by multiple sources. I do not know about the advantages on paint, but if you never let it come in contact, you shouldn't have a problem anyways.

[oruro]

Stay with the manufacturers recomentation.