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[tidla]

things are always improving, knowing what naff fluid can do, i have always used the best standard fluid (dot4?)

read a thread which refered to "yellow fluid"

new product??

[Broomies Mate]

Glycol-based (DOT 3, 4, 5.1)
Silicone-based (DOT 5)

Don't know about this Yellow Fluid.  Possibly Urine? 

[tidla]

Glycol-based (DOT 3, 4, 5.1)
Silicone-based (DOT 5)

Don't know about this Yellow Fluid.  Possibly Urine? 

well they stick it in everywhere else these days so why not!!

[Kevin Wood]

Be very careful with DOT 5 silicone fluid. It is not compatible with mineral fluid and best avoided unless you're filling a brand new system or have flushed it thoroughly and replaced the seals. Even then I wouldn't bother.

DOT 5.1 is an enhanced specification mineral fluid with a higher boiling point which is compatible with DOT 4. For road use, there's probably no reason to change from DOT 4, IMHO.

Kevin

[Broomies Mate]

Be very careful with DOT 5 silicone fluid. It is not compatible with mineral fluid and best avoided unless you're filling a brand new system or have flushed it thoroughly and replaced the seals. Even then I wouldn't bother.

DOT 5.1 is an enhanced specification mineral fluid with a higher boiling point which is compatible with DOT 4. For road use, there's probably no reason to change from DOT 4, IMHO.

Kevin

Completely agree.  Silicone based brake fluid (DOT 5) wont 'combine' with water, so it pushes it all into one place (correct me if I'm wrong Kevin), whereas the Glycol based fluids can cope with water to a degree.

ANY braking system out there which has run with Glycol based fluid has water ingress, it's a fact that we have to deal with, hence replacing fluid every, say, 2 years is important. Even though the Silicone based fluid is better (it wont allow water ingress), it is ONLY applicable to systems which havent had any of the former fluid.

[Kevin Wood]

Completely agree.  Silicone based brake fluid (DOT 5) wont 'combine' with water, so it pushes it all into one place (correct me if I'm wrong Kevin), whereas the Glycol based fluids can cope with water to a degree.

Yep, that's right. I was struggling to remember exactly why. Mineral fluid will absorb a certain amount of water and whilst this results in it losing its properties over time is still basically safe. With silicone, if the system does collect any moisture, it tends to work its' way to the extremities of the system - the slave cylinders, which also get hot. The water vapourises and you've lost your brakes.

Kevin

[tidla]

isnt that the problem with brake fluid, it absorbs water.
the only place this can happen is the vented area (master reservoir)

as long as the seals can cope with the new fluid, isnt that a good thing??

(total fluid change)

[Broomies Mate]

Completely agree.  Silicone based brake fluid (DOT 5) wont 'combine' with water, so it pushes it all into one place (correct me if I'm wrong Kevin), whereas the Glycol based fluids can cope with water to a degree.

Yep, that's right. I was struggling to remember exactly why. Mineral fluid will absorb a certain amount of water and whilst this results in it losing its properties over time is still basically safe. With silicone, if the system does collect any moisture, it tends to work its' way to the extremities of the system - the slave cylinders, which also get hot. The water vapourises and you've lost your brakes.

Kevin

Thanks Kevin.

Just to add to this for anyone without knowledge of brake fluid..............

Water will get into the system.  This is because the rubber hoses are actually permeable.  Small amounts of moisture enter the system and the Glycol (or Mineral) based fluids absorb it.  This then reduces the boiling point of the fluid.  Brakes get extremely hot!!!!! Water boils at 100celcius, DOT 4 boils at 230celcius.  Add water to that, and the boiling point of your bake fluid can reduce to 155celcius.

Boiling brake fluid = extremely poor brakes, or even no brakes.

The new DOT 5.1 mineral fluid boils at 270 celcius, and as Kevin mentioned earlier, for normal road use (assuming proper maintenance procedures are followed) DOT4 is fine (even overkill to be honest).