Hello,

             With the first scheduled service a couple of months away for my 2023 Fiesta when booking I am sure the dealer will ask me if I want a brake fluid change.  Certainly don't mind paying for it as an extra if required but didn't need it the last time I took a car for a scheduled year 2 service.  But, is it essential for the Ford warranty ? And have other Fiesta mk8 / mk8.5  owners had theirs done at this interval regardless of warranty ? Thanks.

If it does affect warranty, it would only be with brake system faults.  For example, they can't get out of paying for a failed wetbelt because the brake fluid wasn't changed.

15 minutes ago, TomsFocus said:

If it does affect warranty, it would only be with brake system faults.  For example, they can't get out of paying for a failed wetbelt because the brake fluid wasn't changed.

I wouldn't put it past a manufacturer to try and do that though. 😉 

@MCF It is worth noting in case you're not aware, brake fluid is hydroscopic - it absorbs moisture from the air.  So changing it every couple of years is recommended, the same as coolant.  Most folk don't bother though.

Ford coolant is rated for 10 years.  That's generally done with the timing belt & waterpump.

Never bothered with this and my brakes have always been rock solid. Maybe if you drive 30,000 miles a year up and down the Andes on your commute things might be different. 

So I reckon I've saved 50p per week, which is nothing, given the costs of buying/leasing/changing/fuelling a car.

...or £1000 over 40 years, which is something! 

Warranty? Maybe ask Ford...

I change my brake fluid when it reaches 3% water content. which for me works out to about 4 years. 

Thanks everyone for answers so far.  On a side note does anybody use those testers with the prongs on to test for water content?. Something I was thinking of adding to my kit.

7 hours ago, cjay1 said:

I change my brake fluid when it reaches 3% water content.

I find the whole notion of the hydraulic brake system absorbing water, perhaps a little exaggerated.

Now I fully understand and accept that brake fluid is hygroscopic and left exposed to the open air it will given enough time absorb water from the atmosphere.

The problem is that in order for any brake system to work it has to be a sealed system. Any hydraulic leak no matter how small would degrade the braking efficiency and eventually lead to a failure of parts of the system. So if we accept that a good working system is in fact sealed then the only possible point of contact with the air would be through the tiny vent hole in reservoir filler cap.

If the entire hydraulic brake system holds for the sake of calculations, 1000ml and of that volume there is on average 200ml held in the reservoir, then only that brake fluid could be exposed to the atmosphere. Of course any moisture could then slowly dissipate through the entire system. However only the surface of the fluid held in the reservoir is in contact with the air, which would mean the process to get the entire capacity of 1000ml to absorb 30ml (3%) of water would take many, many years, probably a decade or more.

Finally there is the question of where is does the extra volume of water fit ?

Interested to see what others thoughts on the matter are.

 

1 hour ago, unofix said:

I find the whole notion of the hydraulic brake system slowly absorbing water a little difficult to grasp.

Now I fully understand and accept that brake fluid is hygroscopic and left exposed to the open air it will given enough time absorb water from the atmosphere.

The problem is that in order for any brake system to work it has to be a sealed system. Any hydraulic leak no matter how small would degrade the braking efficiency and eventually lead to a failure of parts of the system. So if we accept that a good working system is in fact sealed then the only possible point of contact with the air would be through the tiny vent hole in reservoir filler cap.

If the entire hydraulic brake system holds for the sake of calculations, 1000ml and of that volume there is on average 200ml held in the reservoir, then only that brake fluid could be exposed to the atmosphere. Of course any moisture could then slowly dissipate through the entire system. However only the surface of the fluid held in the reservoir is in contact with the air, which would mean the process to get the entire capacity of 1000ml to absorb 30ml (3%) of water would take many, many years, probably a decade or more.

Finally there is the question of where is does the extra volume of water fit ?

Interested to see what others thoughts on the matter are.

 

Here are my thoughts and experience. 

As you say the Cap is not sealed, I don't know how quickly osmosis allows moisture to spread throughout the system.

I did once have a Brake Pedal to the floor situation because the Fluid boiled. One of the Rear Brakes was binding and it was an old car that probably never had its DOT 3 Fluid ever changed. And it was boiling because I let things cool down and was able to drive home, so since then I change my Fluid at least once every two years.

The other thing that worries me is that not only is the Master Cylinder near the Reservoir, but so is the very expensive ABS Pump. I don't think water would do either of these things any good.

 

Some great responses here. In 2 years the cap on mine has never been off and that area gets a dry clean regularly. No actual water comes in to contact with the cap with maybe the exception of a bit of damp on a chilly morning I would expect but would surely take such a long time to absorb upto 30ml as Unofix said.

I have never changed the brake fluid in any car that I have owned. The oldest one was sold when it was 10 years old. I have also never had a problem with brakes that could in any way be related to the fluid.

I've also never changed brake fluid as part of regular maintenance and never had any issues with it.

Generally a caliper or drum cylinder will fail eventually and the fluid will get changed at that point.

With regards to wetting the reservoir though, there's plenty of water vapour in the air, so liquid water doesn't actually need to go near the reservoir.  Same issue with engine oil, it gets contaminated with moisture from the air if the engine isn't run frequently and thoroughly warmed through each time.

1 hour ago, TomsFocus said:

Generally a caliper or drum cylinder will fail eventually and the fluid will get changed at that point.

And that's where problems can occur. The system will probably not be fully bled so the fluid with the worst contamination may end up nicely spread inside the Master Cylinder and ABS unit and corrode things or maybe near the Calliper where it can get hot and boil as per my first post.

You've got to ask yourself why every manufacturer recommends that the Fluid is changed at least every two years and I must remember not to buy a used car from some of you guys😅 

I've just had my motorbike MOT'd today (yes, it did pass). While taking it to get tested I was thinking that I've never even considered changing the brake fluid in it. I also noted that the reservoirs (two, one front and one back) are both fully sealed with no vent hole.

The bike garage MOT tester said changing the brake fluid was not something they were asked to do regularly, and it mostly only happened if brake callipers were replaced.

53 minutes ago, Tizer said:

And that's where problems can occur. The system will probably not be fully bled so the fluid with the worst contamination may end up nicely spread inside the Master Cylinder and ABS unit and corrode things or maybe near the Calliper where it can get hot and boil as per my first post.

You've got to ask yourself why every manufacturer recommends that the Fluid is changed at least every two years and I must remember not to buy a used car from some of you guys😅 

I tend to do it every 4 years (if I remember) and if the fluid has changed from a olive oil yellow to a darker apple juice it's definitely due, and if it has turned green (yes I know you can get dot 4 in green but in general it shouldn't be green) then you have left it too long and you have started corroding something in your braking system (usually caliper pistons and drum slaves).

11 hours ago, Tizer said:

And that's where problems can occur. The system will probably not be fully bled so the fluid with the worst contamination may end up nicely spread inside the Master Cylinder and ABS unit and corrode things or maybe near the Calliper where it can get hot and boil as per my first post.

You've got to ask yourself why every manufacturer recommends that the Fluid is changed at least every two years and I must remember not to buy a used car from some of you guys😅 

I've never boiled brake fluid or had any loss of brake force at all.

I did have a couple of dodgy moments locking up in my very first car without ABS on wet/loose ground - that was enough for me to make ABS a requirement on all cars I bought after that.

If I'd had the same experience as you with boiling brake fluid then I probably would change it more regularly, but I haven't.

Also, if I was going to do any track driving, with heavy brake usage, I'd change it regularly.  But for light road use I just haven't found it necessary at all.

Manufacturers also make other servicing recommendations that I haven't found to be necessary from light road use.

I had my previous Fiesta changed at 3 years, and I'm doing the same with this. My usual dealer tests  for moisture content and discoloration at every service anyway, as does the independent where we have my wife's car serviced.

On the original point - I've never had it raised as a warranty issue, either at Ford or any other franchise.

 

 

The 2 yearly brake fluid interval is essentially an save fords ***** if a crash was to be attributed to brake failure (the same as all other manufacturers) it's only actually necessary if you either: a, live in a hot humid country aka Amazon rainforest or tropic similar in temperature and humidity, or b, you consistently get your brakes very hot. I'm talking discs glowing red like for instance you drive it hard round a track a lot.

1 hour ago, Neb_engineer said:

it's only actually necessary if you either: a, live in a hot humid country aka Amazon rainforest or tropic similar in temperature and humidity, or b, you consistently get your brakes very hot. I'm talking discs glowing red like for instance you drive it hard round a track a lot.

Or if your Brakes are binding like what happened to me many years ago. What happened to me was real not theoretical.

From what I see, the cap has a rubber diaphragm under it so even that is sealed against any moisture getting into the system?
With earlier (DOT3?) fluids when bled, it came out much darker at the calipers at first, indicating (to me) that it was being degraded by heat.
Since DOT 4 I haven't noticed this.
We (MBH and myself) do flush through with 500 ml at 2-3 year intervals just to try and keep to Ford's  "orders" as we don't intend to (ever at the moment) get rid of it.
It does have the good effect of ensuring that the nipples can be loosened in case any work is needed on the braking system (this year, fitted stainless steel ones)
But, as mentioned, no one else we know has ever done or mentioned this job.

Don't know the cost but it must be a nice little earner?

13 minutes ago, Shearers said:

From what I see, the cap has a rubber diaphragm under it so even that is sealed against any moisture getting into the system?
With earlier (DOT3?) fluids when bled, it came out much darker at the calipers at first, indicating (to me) that it was being degraded by heat.
Since DOT 4 I haven't noticed this.
We (MBH and myself) do flush through with 500 ml at 2-3 year intervals just to try and keep to Ford's  "orders" as we don't intend to (ever at the moment) get rid of it.
It does have the good effect of ensuring that the nipples can be loosened in case any work is needed on the braking system (this year, fitted stainless steel ones)
But, as mentioned, no one else we know has ever done or mentioned this job.

Don't know the cost but it must be a nice little earner?

It can't be sealed, if it was  then things would not work because there would be a vacuum created as Pads wore down.

When changing Pipes on cars without the Float attached to the Cap I would screw the Cap on with a polythene bag under it to form a seal and there would be no Fluid loss. If I just left the Cap on there would be a Fluid loss.

I fully agree with everything else that you said though.

Just to that query on dealer pricing it is roughly £65 if added to service.

That's probably not too bad a cost, considering usual dealer labour rates.

22 hours ago, Shearers said:

From what I see, the cap has a rubber diaphragm under it so even that is sealed against any moisture getting into the system?
With earlier (DOT3?) fluids when bled, it came out much darker at the calipers at first, indicating (to me) that it was being degraded by heat.
Since DOT 4 I haven't noticed this.
We (MBH and myself) do flush through with 500 ml at 2-3 year intervals just to try and keep to Ford's  "orders" as we don't intend to (ever at the moment) get rid of it.
It does have the good effect of ensuring that the nipples can be loosened in case any work is needed on the braking system (this year, fitted stainless steel ones)
But, as mentioned, no one else we know has ever done or mentioned this job.

Don't know the cost but it must be a nice little earner?

Dot 3 broke down far faster and absorbed moisture faster than dot 4

On 7/4/2025 at 3:44 PM, Tizer said:

It can't be sealed,

As far as I can see it is a thin, flexible diaphragm that can move as the fluid level changes: