Posted on 29/11/2019 16:05
My Ford Mondeo has a service interval of every 2 years or at 18,000 miles whichever is the sooner. I have been told that Ford now recommend a change of brake fluid every two years - ie at every service in my case. This seems to be a new recommendation. Is it common with other makes of cars or is it just another main dealer rip off?
Posted on 29/11/2019 16:55 byIn my opinion the fluid is more likely to deteriorate on a low mileage car than a high as it becomes prone to collecting condensation,
Not disagreeing but it seems strange. A brake system is bled of air and is largely a contained system filled with brake fluid. The condensation comes from water vapour in the air. How does that enter the system? The only air fluid interface might be thought to be the breather hole in the reservoir. Any water vapour entering will be a very small amount and the water is lighter than the brake fluid.
Posted on 29/11/2019 20:43
As has been correctly pointed out earlier most, automotive use brake fluids, are "hygroscopic", they can absorb water, into solution.
This brings two ramifications, one potentially safety critical, the other a cause for incipient corrosion.
The big danger is the water in solution can boil, at quite a bit lower temperature blowing out the vital liquid so next time you plant your foot you have no braking. Without the water the system design should never reach the boiling point of the fluid.
The obvious second issue is water supports corrosion so overtime there will be brake failure arising from that.
Some systems don't have an air vent and are sealed from this issue by an air to fluid diaphragm.
Fluid change time is an estimate, a challenging one to make as there are many variables, where used, frequency of use, humidity and probably many more.
I suspect the vehicle makers cover the worst possible combination recommending a change time that they feel presents no risk, whilst not overly adding to user costs.( they must do this as many fleet users pay great attention to through life ownership costs)
Me I am a three year change on brakes, 6 on clutches, not that I recommened you do anything other than what the maker suggests.
Posted on 01/12/2019 12:14
I agree with those who say the fluid is hydroscopic. It does absorb water from the atmosphere. Many years age a chap I worked with whose job was to examine vehicles involved in road collisions was issued with a new bit of kit to test brake fluid for water content and deterioration.
So out of interest I tested my own vehicle which was about 5 years old and had never had a change of fluid. The fluid was contaminated badly with water and not up to the job it was designed to do so I had it changed immediately.
Water in brake fluid when over heated by braking will boil and they will not work, this is called brake fade.. You cannot compress a fluid but you can compress a gas or vapour.
My own vehicle brake fluid is changed every two years. I recommend you err on the side of safety.
Posted on 01/12/2019 14:45
I have the fluid in our cars changed every two years regardless of whether specified or not. Its hygroscopic nature means that there is a risk of it accumulating water which will corrode the bores of calipers. Like lots of things with cars, if one is going to keep them it's worth doing preventative maintenance
JohnM20
Caravanner from Derbyshire