Brake fluid change criteria?

[MikeM46]

One of the FB Superb forums had a “discussion” about brake fluid changing. Seemed all over the shop … is there anything authoritatively available?

[numskull]

Manufacturers dealers will say every two years as brake fluid draws-in moisture from the air, lowering its boiling point and thereby its effectiveness. Now, this makes complete sense doesn’t it, with it being a product in a completely sealed system and with an air pocket it it’s top. 30-odd years ago, no one “changed” their brake fluid, it was just topped-up when brakes were bled when needed or possibly changed when a master cylinder failed. Now obviously this “oversight” led to huge numbers of accidents all over the world, as owners unknowingly drove round with water slopping around in their brake fluid boiled-away, and left them without effective brakes or, indeed, no brakes at all and components and pipework rotted from the inside-out.
Nah, never happened; its another way to take your hard-earned, but what do I know. So if you feel you must on “safety grounds”, then every five years would seem to be more reasonable than the £70-100 they kerchang every two years.

[Legion]

No.

 

It depends on the fluid your using and how much water its absorbing from the atmosphere, how much work the brakes are doing and what is the performance expectation.

 

As a general rule its normally done at 2 year intervals as part of routine maintenance. The fluid isn't expensive.

 

How and when to change your brake fluid | Haynes Manuals

 

BRAKE FLUID CHANGE | CASTROL UK & IRELAND

 

 

 

[Bap33]

Skoda recommends a brake fluid change after 3 years and then every 2 years. 

 

If you need a how to guide, just have a look here:

 

[310golfr]

ii just test the moisture level with a tester and if it says no moisture, then it does'nt need changed 

 

[ApertureS]

Qualified mechanic here -

 

Skoda and other maindealers set a time limit on brake fluid and probably dont even own a hygroscopic tester.

 

The brake fluid manufacturers state that between 0-1% water concentration is perfectly fine.

Between 1-2% there is a slight loss of hydraulic efficiency when the fluid heats up.

Anything over the 2% is when they class the fluid as a significant lower efficiency.

 

The efficiency goes down when the fluid heats up causing cavitation in the lines and reducing the effectiveness of the brakes.

 

 

Now from a prospective of working on cars and my own and not a sales man - Have it tested ideally at the reservoir and also at the caliper as these will be points of ingress. Chances are it will be in the orange/green zone. Dont change it. But that being said the longest id leave it before changing is 4/5 years depending on driving style. 

[SurreyJohn]

2 hours ago, Bap33 said:

Skoda recommends a brake fluid change after 3 years and then every 2 years. 

 

And this is one of the unexplained oddities why the brake fluid they use in the factory is good for 3 years, but the same brake fluid used by Skoda dealers is only good for 2 years when located in same place in same vehicle !
 

I would suggest 4-5 years unless you are the kind of person who gets the brakes very hot by regularly descending mountain passes, or hauling unbraked trailers regularly 

 

 

[J.R.]

And as someone that does I can tell you that you dont need a service shedule or an electronic tester (which I have) to know when you have excess H20 in the calipers.

 

It has only ever once happened and was nothing to do with absorbtion from the atmosphere or through the flexible hoses (another myth based on a theoretical but unmeasurable science) it was on a Galaxy that had a recall because rain running down from the scuttle was falling directly onto the master cylinder cap which had an upturned U section where the float switch could swivel in it, the water went straight in and displaced the brake fluid (less dense) then travelled down and settled in the front brake calipers, they were full of rusty water and zero fluid, the concentric clutch slave cylinder failed also later on.

 

That braking system running on pretty much water (the perfect hydraulic fluid but for one small detail!) worked perfectly until abused under very extreme circumstances.

 

My MK1 Octavia had the fluid checked every year using the most expensive and regularly calibrated tester during the Télé-thon at the Lycée Pro where I volunteered, I also checked it with my own tester, it never showed any measurable contamination and was scrapped at 17 years old and 325000 miles with the original fluid in perfect condition.

[Bap33]

What may be good for a car might not for another one.

I've change brake fluid on my mom's Citroën C3 MY2010 (please don't laugh 😁)... after 10 years. The brake pedal behavior was like night & day after brake fluid change!

If you have a look to my how to guide, you can notice that a 3 year old brake fluid starts getting dark. Brake fluid property may not be drastically affected (I mean not to an extent your can feell it easily under your foot) but... I assume it may start increasing braking distance. 1 meter more, maybe a meter too much / too late...

 

I'm not lecturing anyone. Just sharing a point of view.  

[J.R.]

The old Citroens that used mineral hydraulic fluid in the fancy brake systems certainly benefitted from a change of fluid.

 

Discoloured brake fluid will not add to your braking distance, for the amount of heat generated in normal braking you would get equal brake performance and stopping distance were you to use tap water, its in extremis that any significant water content can make its presence felt, when carrying or towing overloaded & repeatedly braking from high speed, mountain descents, track days etc, any involved driver would know all about it through the change in pedal feel.

 

There is a danger that a carefull suburban driver could be unaware having never put the brakes to the test until an emergency stop involving some or all of the other contributory factors. I regularly deglaze my brake pads & make sure the ABS kicks in as most of the time the brakes get very little and very gentle use.

[numskull]

7 hours ago, ApertureS said:

Qualified mechanic here -

…… the longest id leave it before changing is 4/5 years depending on driving style. 

What he said….

[Bap33]

5 hours ago, J.R. said:

The old Citroens that used mineral hydraulic fluid in the fancy brake systems certainly benefitted from a change of fluid.

 

A MY2010 C3 is definitely not one of these.  

[bigjohn]

I err on the safe side so I stick to manufacturer intervals (3 then 2 years thereafter).

 

I used to restore many cars and the hydraulic fluid I've drained from many a car has been frankly awful be it dark brown / milky etc. I also remember doing the brake fluid on my Dad's 1986 Volvo estate in the early 90's - it looked like the master cylinder reservoir was black but it  changed colour as the new fluid was bled through. There were also signs of rust in the extracted fluid. The dual circuit light was upset for a few weeks afterwards. Saying that it was an amazing system - each front calliper had two separate circuits!

 

In conclusion 2 years might be a bit OTT but in my experience 6 years is Houston. As it doesn't cost much really I'll stick  to OTT.

Edited 23 April, 2022 by bigjohn

[Superbio]

I just had mine changed in my 2017 Superb 2 days ago. Probably the first time it's been done in its life. They still felt fine but it didn't seem wise to leave it much longer

[Danoid]

I would have thought you’d need something like VCDS to purge the ABS.

 

Is that not the case or just something not necessary?

[Bap33]

On 24/04/2022 at 14:03, Danoid said:

I would have thought you’d need something like VCDS to purge the ABS.

Nothing like that mentioned in the Skoda workshop manual.

[StevesTruck]

Not unless you let the fluid level drop too low. Yeah, there might be a tiny drop of old fluid left at the abs pump, but by no means anything to worry about. 

 

 

[MikeM46]

Lol ... thanks for all the input ... still at "all over the shop"!

Anyway, being replaced Friday, along with re-gassing the aircon ... another great discussion topic!