Mixing Brake Fluid

[wish mine was orange]

Hi ,

i got a friend who needs to know he has to top his brake fluid up with DOT3 fluid but i have a DOT 4 fluid that on the container states it can be mixed with other types of brake fluid?

is this ok to do?

thanks

 

[fingers99]

It'll mix, but DOT3 is obsolete. May well be past its sell by date and gone off.

 

[Peter Pick-Up]

Wrong, DOT 3 is not obsolete at all.
In fact, lots of car/ bikes are designed to use only DOT 3....
Lots of American cars and bikes, way into the nineties, use ONLY DOT 3 fluid.
Any decent part shop can get quality DOT 3 brake fluid for you, no problem.
And yes, you can mix it with DOT 4, but as this is a complete different product, I wouldn't recommend it.
By no way DOT 4 is a better quality over DOT 3, again, it's just a different product.

 

[sludgeguts]

Personally, I wouldn't bother mixing, just drain the lot and add fresh.
A really easy job if you use an eezi bleed kit.

 

[fingers99]

Wrong, DOT 3 is not obsolete at all.
In fact, lots of car/ bikes are designed to use only DOT 3....
Lots of American cars and bikes, way into the nineties, use ONLY DOT 3 fluid.

You pretty much make my point for me. It may be absolutely the right stuff for a P 47 Thunderbolt, or a Harley designed in the 1930s, or even a hemi charger. But it has no place whatsoever in a modern European vehicle. And in almost all cases (only a few chumps at Toyota seem to be holding out on this) DOT 4 can be used as a straight substitute.

By no way DOT 4 is a better quality over DOT 3, again, it's just a different product.

Well, the DOT bit refers to the US Department of Transport. By DOT specifications, DOT4 must have a boiling point 25 degrees C higher than DOT 3 (dry) and 15 degrees higher wet. It would seem perverse in the extreme to argue that DOT 4 was not of better quality.

 

[Peter Pick-Up]

Again, common disbelieve, a higher boilingpoint doesn't mean higher quality.
It IS a complete different product.
To achieve that higher boilingpoint, DOT 4 has a higher viscosity, meaning it is "thicker" so it will flow less easy compared to DOT 3.
If a brake system is designed for DOT 3, it will work best with the least "thick" fluid= DOT 3, and you MAY get problems with DOT 4 or higher ( DOT 5.1, don't use DOT 5, as this is silicon based, and will NOT mix.....!!)
Almost all fast European cars into the eighties run on DOT 3....!!

 

[fingers99]

Again, common disbelieve, a higher boilingpoint doesn't mean higher quality.

It means a higher specification, by definition. A product which will work in more extreme circumstances. If this doesn't mean "higher quality", I'm a dutchman.

It IS a complete different product.

Completely is over-egging it. The silicone fluids are "completely" different. DOT 3 has a similar composition/chemical make up to DOT 4.

 

[Ffoxy]

It means a higher specification, by definition. A product which will work in more extreme circumstances. If this doesn't mean "higher quality", I'm a dutchman.Completely is over-egging it. The silicone fluids are "completely" different. DOT 3 has a similar composition/chemical make up to DOT 4.

Peter Pick-up actually is...

 

[Peter Pick-Up]

It means a higher specification, by definition. A product which will work in more extreme circumstances. If this doesn't mean "higher quality", I'm a dutchman.


Completely is over-egging it. The silicone fluids are "completely" different. DOT 3 has a similar composition/chemical make up to DOT 4.

I'm very sorry, but you are wrong again.
DOT 3 is chemically totally different from DOT 4, altough they can be mixed.
In practice one wouldn't notice any difference, but I wouldn't use DOT 4 in a track car, with a brake system designed for DOT 3 fluid, like f.i. most Ferrari's from the eighties. ...
But again, for a car in normal everyday road use, it wouldn't matter at all...
I own, among others, an '85 Alfa Romeo GTV-6, and I use ONLY DOT 3 brake fluid in that car, I also own a '88 Pontiac Firebird Formula 350, and again, ONLY DOT 3 in that vehicle.
But I do use DOT 4 in My Ducati motorcycle, and the Fiat Palio as well, I change it every two years in all vehicles...!!

 

[Peter Pick-Up]

http://www.stoptech.com/technical-support/technical-white-papers/brake-fluid

 

[slugworth1987]

why not just 5.1 in yout 3 applications? you say thinner is better well there you are ;-)

 

[Peter Pick-Up]

Because they were not designed for DOT 5.1......!!!
I like to try and test F.I. better quality oils, tires, exhausts etc. but I just stick to what the manufacturer tells me to use in my brake systems, as they are one of the most important ( safety) parts of the vehicle.

 

[fingers99]

I think I've always used DOT 4 in my Ducatis, though I suspect DOT 3 was recommended for the bevel twins. I know people who raced with silicone DOT 5 in BOTT without ill effects.

My conclusion -- in 98% -- or more -- of cases, moving to a later DOT will be fine (although care should be taken with silicones).

Do manufacturer's design with a particular fluid in mind, or simply test with a given fluid? I'm inclined to believe the latter. And snotty enough to believe I can do my own testing.

Peter Pick-up actually is...

:bang: Some of us here can still understand irony. We're a dying breed, but............:bang:

 

[Peter Pick-Up]

I think I've always used DOT 4 in my Ducatis, though I suspect DOT 3 was recommended for the bevel twins.

My Mille MHR Beveltwin takes DOT 4...!!

 

[fingers99]

Mine were much earlier -- 450 Desmo and first generation 900SS.

 

[Peter Pick-Up]

Mine was the very last Taglioni Bevel Twin....!!
And I use ONLY Castrol DOT 4 in it....!!

 

[fingers99]

But the question maybe should be, "what was the best Taglioni designed bike?"

For the road, I'd vote the iconic 750SS and the 350 Desmo, for race, it has to be the 125GP.

 

[Peter Pick-Up]

Depends on the way you look at it.
Technically spoken the Mille was the best bevel twin engine, the most reliable etc.
Altough the chassis was bad.
I have convert mine to a 900SS Verllichi chromo competition chassis, together with an aluminum box section Verllichi rear swingarm and a Marzochi M1R 42mm front fork.....!!

 

[fingers99]

One I really lust after is the Supermono. I only ever saw one (broke lap record at Mallory Park, finished 2nd after a bad start and the race stopped early after an accident). Gorgeous little bike, and, although Bordi and Domenicali designed it, it's said that Taglioni was wandering about the shop, saw a rough sketch, and suggested the counterbalancing conrod. (But this may just have been a kindness.)

I feel the need for another Duke, so may go after a 748 -- they're fairly cheap now -- when I sell the house. Plenty fast enough for someone eligible for a free bus pass...........

 

[Peter Pick-Up]

OK, that one will us DOT 4 for sure...!!
I only like Bevel twins, and specially the Hailwood versions, that's why I build my own MHR, based on a Mille engine, back in 1988.

(The only non Bevel I like is the '85 F1.....!!Saw ( and heard..!!) it raced by Luccinelli in Assen in the Eighties, made a huge impression on me).

But the must impressed I was by the NCR Bevel Twin endurance Ducati's raced by Victor Palomo &co. at the 8 hours of Assen, early 80's, the sound and looks were unbelievable....!!
Than I decided I had to have one of those, one time....!!