brake fluid

[m4nesh]

hello all

What is the general consenus on changing your brake fluid? I know that your supposed to change the brake fluid every 2 years but that is according to my VW mechanic mate a money spin off for the VW garages.

After checking my Service book my brake fluid hasn't been changed since 1995.
Does old brake fluid lose its cooling properties over time?
When should you change the brake fluid?
I realise that in the case of leaking or contamination of the brake fluid then bleeding is required.

By the way my brakes work fine!

[Gambit]

think it absorbs moisture which then makes the brake pedal more spongy - though im not sure what DOT fluids this applies to!

[frankerooney]

I think they say to replace the fluid cos it absorbs moisture over time and it can make the brake lines which are only steel rust from the inside out! Bleeding them isn't hard - just just up the car and do the brakes in the right order - i think it's front right, rear left, front left, rear right? Also try and jack the rear of the car quite high or force the load valve under the rear axle upwards to allow free flow. Watch undoing the bleed valves - they can shear off if they're rusty - I found that the trick is to put some pressure on with a spanner and lightly tap round the outside of the valve end until it frees up?? A brake bleed kit makes life loads easier.
 

[TimMK28v]

The DOT level is effectively a quality level.
Most road cars run DOT4 which is a silicone based fluid...this absorbs moisture, hence the spongey pedal found after a while.
DOT 5.1 is an improvement to the above, but it is not silicone based and has a higher boiling temperature. Useful if driving hard!
For more extreme uses you can also get hold of ultra high temperature fluids. Something like Castrol SRF. Aparantly on older seals using 5.1 or higher can lead to fluid weaping from around the seals. But this is not something I have personally had a problem with.  

[golfvr6]

It is recommended to change the fluid every 2 years as it absorbs moisture from the air, this will cause the boiling point of the fluid to lower until it could be potentially dangerous.

[workhorse '90 8v]

a mechanic friend changes his yearly on a '87 Quattro    (verynicemotor)

[mk1]

Found this....

As a DOT3 or DOT4 brake fluid absorbs water, its boiling point decreases. It can absorb water from the air, which is why you should avoid opening your car's brake fluid reservoir. For the same reason, you should always keep containers of brake fluid tightly sealed.
 
DOT5 brake fluid is also known as "silicone" brake fluid
DOT5 fluid does not absorb water. This means the boiling point will remain relatively stable, but it also means that any water that does get into your brake system will tend to form pure water pockets, which could cause brake corrosion.
I would change the fluid any time I was working on the brakes hydraulics, bleeding them always makes them "feel" better .
Use dot 4 and 24 months is ok.
Steve.

[modulater]

the fact it absorbs water makes it "hydroscopic".


Try saying that to the spotty plums at kwik fit.

[m4nesh]

cheers lads for the information it is very informative.....looks like I'll have to change the brake fluid seeing as it hasn't been changed for about 8 years....next service is 8 thousand miles....hope it lasts till then

cheers