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Dot 4....Dot 5.1 and mineral oil???Oh Why??

RMboy

Monkey
Dec 1, 2006
879
0
England the Great...
SO you have all of the above, i cant seem to find out what the difference is between them... As in what advantages each would have over the other

I know that Mineral oil does not eat you paint and It apparently does not absorb water...?(is this true?) So this must be a bonus over the Dot fluids.... But then there must be a reason to use them...

Also heard that Avid and hope changed to Dot 5.1 this year which has a much hight boiling point....

Pleas help a poor boy understand:busted:
 

davep

Turbo Monkey
Jan 7, 2005
3,279
0
seattle
DOT 3, 4, and 5.1 are glycol based (same as anti-freeze). They are water miscable and thus absorb water out of the atmosphere (if open to the atmosphere). these are all (for the most part) interchangable.

DOT 5 is silicone based and does not absorb moisture.

mineral oil is a petrol based oil. It does not absorb moisture.

The problem with fluids that do not absorb moisture is that any moisture in the system (due to condensation via temp or pressure changes) is not absorbed and left as water droplets within the system. This water not only boils at a MUCH lower temp that the fluid, it can also cause rust/oxidation within the brake system. Water is also heavier than the fluids and thus will migrate to the caliper (the hottest point in the system) increasing the possibility of boiling (and loss of brake force)


It is true that the glycol fluids absorb moisture, and this in-turn lowers the boiling point of the fluid (look at 'wet boiling point')..BUT because the moisture is integrated into the fluid, rust and corrosion is prevented (think coolant/anti freeze in a cast iron block engine). The boiling point is lowered as the % of moisture goes up, but usually the wet boiling point is high enough to prevent boil if you change fluid on a regualr basis (and it is certainly significantly higher than the boiling point of the free water in a non-miscable fluid).
 
Keep in mind that brakes specifically designed for Dot cannot use Mineral oil and visa versa. I have been using brakes with DOT since I started riding but am switching to Shimanos for the year which use Mineral Oil. Aside from bleeding technique, anything different in how they actually work, any specific tricks to make them run well?
 

General Lee

Turbo Monkey
Oct 16, 2003
2,867
0
The 802
just curious, but i always read that DOT fluid can 'ruin your paint.' Having spilled it all over every bike i've owned since 1998 i've never experienced any damage to the paint (or thermoplastic in the case of my Lobo).

obviosly it is--or was--a hazard to some kinds of paint, but i wonder if it's fairly innocuous to modern day paint jobs; the warning being akin to the 'clearcoat safe' label we see on car wax.


i've had different brakes that ran on one or the other with no noticeable difference. Rotors get hot, but not nearly as hot as those on a car or motorcycle. I'm a fan of DOT though, for the simple reason that--it being a staple of every gas station and convenience store--i can find a fresh bottle of it on about every corner. you can be out of luck if you run out of mineral oil or spill it on the ground. last i checked the mineral oil sold a drug stores is thicker than the stuff used in brakes. But, in its defense if you use mineral oil you'll always be prepared in case you need a laxative.
 

Transcend

My Nuts Are Flat
Apr 18, 2002
18,045
0
Towing the party line.
just curious, but i always read that DOT fluid can 'ruin your paint.' Having spilled it all over every bike i've owned since 1998 i've never experienced any damage to the paint (or thermoplastic in the case of my Lobo).

obviosly it is-or was-a hazard to some kinds of paint, but i wonder if it's fairly innocuous to modern day paint jobs; the warning being akin to the 'clearcoat safe' label we see on car wax.
Pretty sure it's the clear protecting your paint. It's much harder than the actual paint itself. On bare paint it does a pretty good job.
 

davep

Turbo Monkey
Jan 7, 2005
3,279
0
seattle
just curious, but i always read that DOT fluid can 'ruin your paint.' Having spilled it all over every bike i've owned since 1998 i've never experienced any damage to the paint (or thermoplastic in the case of my Lobo).

obviosly it is-or was-a hazard to some kinds of paint, but i wonder if it's fairly innocuous to modern day paint jobs; the warning being akin to the 'clearcoat safe' label we see on car wax.
The vast majority of bike frames are not painted...they are powder-coated...essentially plastic powder/dust that is melted onto the frame. I think this is one of the reasons you see little damage from short term exposure to glycol fluids.
 

jvnixon

Turbo Monkey
May 14, 2006
2,325
0
SickLines.com
I think its almost safe to say that we've all seen what dot brake fluid can do to a set of older hayes brake levers. We've all seen it at least once i'm sure.

Davep i think covered a lot of the reasons why its not so prevalent on your frame.
 

General Lee

Turbo Monkey
Oct 16, 2003
2,867
0
The 802
mineral oil is a lot less toxic too. lick the DOT off your fingers and you can get sick, lick the mineral oil off and you just poop.:biggrin:
 

RaID

Turbo Monkey
Keep in mind that brakes specifically designed for Dot cannot use Mineral oil and visa versa.
Officially that is the case

However mineral oil wont destroy seals because it is less toxic/reactive (whatever you want to call it) than DOT fluids.
I have seen mineral oil been used successfully in a DOT system for an extended period of time without any problems

Definately DONT run DOT fluid in a Mineral Oil System

I have been using brakes with DOT since I started riding but am switching to Shimanos for the year which use Mineral Oil. Aside from bleeding technique, anything different in how they actually work, any specific tricks to make them run well?
The fluid type doesnt have anything to do with the difference in bleeding technique and setup of the brakes. That is governed by the design of the brake system itself.

Shimano brake systems are bled like car systems ie from the reservoir (ie your brake lever) to the caliper. You put fluid in the reservoir, pressurise the system by pumping the lever then release the bleed valve in the caliper.

unlike Hayes for example which are bled from caliper to reservoir ie you put fluid in calliper and push it up through the system to the reservoir in the lever.
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,288
874
My own world inside my head
just curious, but i always read that DOT fluid can 'ruin your paint.' Having spilled it all over every bike i've owned since 1998 i've never experienced any damage to the paint .
Clear coat is protecting the paint, or with Powder coating its just tough enough not to eat up right away, It was the older style laquers and acryllics that would get eaten up when brake fluid would get on them
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,288
874
My own world inside my head
Not on older paints, it was like paint stripper, took about one minute and your paint was done, newer paints yet, just was it down and your good to go, and with glycol fluids, just hit it with some running water. No need for alcohol
 

RMboy

Monkey
Dec 1, 2006
879
0
England the Great...
DOT 3, 4, and 5.1 are glycol based (same as anti-freeze). They are water miscable and thus absorb water out of the atmosphere (if open to the atmosphere). these are all (for the most part) interchangable.

DOT 5 is silicone based and does not absorb moisture.

mineral oil is a petrol based oil. It does not absorb moisture.

The problem with fluids that do not absorb moisture is that any moisture in the system (due to condensation via temp or pressure changes) is not absorbed and left as water droplets within the system. This water not only boils at a MUCH lower temp that the fluid, it can also cause rust/oxidation within the brake system. Water is also heavier than the fluids and thus will migrate to the caliper (the hottest point in the system) increasing the possibility of boiling (and loss of brake force)


It is true that the glycol fluids absorb moisture, and this in-turn lowers the boiling point of the fluid (look at 'wet boiling point')..BUT because the moisture is integrated into the fluid, rust and corrosion is prevented (think coolant/anti freeze in a cast iron block engine). The boiling point is lowered as the % of moisture goes up, but usually the wet boiling point is high enough to prevent boil if you change fluid on a regualr basis (and it is certainly significantly higher than the boiling point of the free water in a non-miscable fluid).
Cool that was a informative post...so there is no real advantage over each system?
 

Rover Nick

Monkey
Oct 17, 2006
280
0
mineral oil is a lot less toxic too. lick the DOT off your fingers and you can get sick, lick the mineral oil off and you just poop.:biggrin:
Ideally you shouldn't be licking any kind of brake fluid off your fingers.
But I will say that I have gotten DOT fluid on my tounge and it tingled really badly. Not very fun