Does Water In Brake Fluid Cause Rust Or Damage?

Note: I will update this page as the experiment goes forward.

Many times we hear how important it is to change the brake fluid often because it is hygroscopic (absorbs water). Then the marketing materials continue about rust forming, exploding brake lines, destroyed rubbers, boiling water and fluid needing to be changed regularly.

The brake fluid is cheap, but it is one of those things which has environmental impact and also monetary cost increase if you keep changing many fluids unnecessarily. Plus, there are literally billions of vehicles use it. Imagine the yearly liquid amount which should be recycled.

Businesses constantly scare people so they keep up with the regular payments. Considering there are over billion vehicles in use. Can you imagine the regular revenue stream from regular purchases of a product like brake fluid. There is no business like fluid business.

Should we be scared of boiling water, rust and corrosion? But we can't see the rust inside the pipes. Is there rust really? or is it a convenient way for companies to scare us? Will the brake pipes burst if we do not change the brake fluid often enough?

Reasoning:

As we all know forming rust requires oxygen. Therefore it should not happen inside brake pipes (because we do not have air in the brake pipes!). Somebody may say, water carries dissolved oxygen what about that? The absorbed water by the brake fluid will not contain oxygen. Because oxygen molecules will not be absorbed by brake fluid.

What about disintegrating rubbers? Brake fluid attacks many things by itself. But having water inside will not cause it to destroy rubbers. Totally made up.

So there remains boiling water. Yes, the brake pad temperatures can reach 200C or higher. But the heat transferred to caliper and the brake fluid is less and locally isolated (the only hot part is around the caliper where piston touches the pad) The absorbed water decreases the boiling temperature of the brake fluid. For dot 5.1 the wet (3.7% water) boiling temperature goes down from 270C to 190C. So it may be possible that a very small amount of brake fluid may boil. But all things considered, it won't cause catastrophic brake failure all of a sudden.

Experiment:

It is simple, I have created a 10% water mixture with brake fluid and dropped copper/steel materials into it.

Preperation:

Used 2 washers, 2 galvanized steel nuts and 2 copper nuts. First I put them into vinegar to artificially rust away the galvanization layer. Since it would just make the rust appear slower.

In the picture above, untouched washer and nut can be seen on the left lower side. Also a set of nuts and washer are in the glass. The other 3 goes to the other glass.

I fill one of the glass with brake fluid which had about 10% water and the other glass is filled with water. I used tap water and it may effect the results compared to brake fluid absorbing water from air directly. However I didn't want to wait for that to happen and I could control the amount of water inside brake fluid better if I put it there myself.

Below is 2cl brake fluid ready to be mixed with  2.5ml water.

Tested the solution using brake fluid tester

Now that the brake fluid tester is proven to be functioning. I have mixed the brake fluid/water in the glass also.

You can see the glass with water on the left also.

Then had to cover the tops with cling wrap to avoid contamination. However I made a 3rd glass where was pure brake fluid with holes on its cling wrap. That is there for following the absorption of water from air (a side experiment)

I may open the cling wrap once in a while and air the fluids, but it should be even better to keep the fluids covered. Because brake fluid system itself is a closed system and keeping the cling wrap will help to emulate it better.

Day 1 (28-Dec-2018):

After few hours of waiting the items in the water glass were covered with bubbles. Then they developed some rust. There was also water condensation on the cling wrap.

I realized that I forgot to wipe the rust from vinegar inside the washer which is in brake fluid. But that is not important. Otherwise there is nothing happening to the items in the brake fluid right now. Also there is no condentation on the cling wrap.

Day 2 (29-Dec-2018):

Actually, it has been less than 24 hours but there is significant progress in the water cup compared to the brake fluid cup. There is no change on materials inside the brake fluid.

Day 8 (05-Jan-2019):

Not much difference visually. The copper nut seem to have lost its copper plating in water. The water seem to have much more particles floating at the bottom. No difference to parts in brake fluid.

Day 17 (14-Jan-2019):

No difference to parts in brake fluid. It is nearly impossible to see the parts inside the water. I will  replace the water with clean water before continuing. Otherwise it will be impossible to see anything there soon.

Day 122 ( 29-Apr-2019):

Still, no difference for parts in brake fluid. The parts inside the water are totally gone under rust pieces.

Conclusion:

At this point I am stopping the experiment as it has been nearly half a year and there is definitely degradation with parts in water but nothing visible with parts in oil.

After rinsing the parts which were under water.  I can see some degradation

However they still seem perfectly fine otherwise!

Also checked the brake fluid glass with air holes on top. It have collected about 3% water in this time. So yes, brake fluid absorbs water.

But overall, it is clear that we do NOT have to worry about water in brake fluid causing rust in the brake system. It seems to be impossible.