Break fluid question

[apl360]

Fucking metric bullshit. I appreciate y’all adding Fahrenheit. Thank U.

metric never made it on the moon. Metric didn’t show Japan the sun (twice) js

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[Evox787]

Fucking metric bullshit. I appreciate y’all adding Fahrenheit. Thank U.

metric never made it on the moon. Metric didn’t show Japan the sun (twice) js

right I don’t even know how much it’s 500 ml but that how the bottle is labeled , OMG I really needed this laugh this morning thank you!

 

[zumbooruk]

I usually replace it every year, but the process on these cars is so different and annoying that it’s been a year and a half, and I’m still running the stock fluid.

Which is why I was looking at fluids with three year change intervals

 

[PNEUMA]

I don’t even know how much it’s 500 ml but that how the bottle is labeled

it is one half liter

 

[Evox787]

Which is why I was looking at fluids with three year change intervals

But to my understanding, brake fluid absorbs water regardless, because of the properties contained in the fluid. I’m probably wrong, but it’s like the oil that claims 10k miles; in reality, no oil is capable of doing that without causing long-term damage. That’s why those cars that sell you the “lifetime” fluid for the transmission or differential are misleading, because oil also loses its properties.

Everyone has their own opinion. One person could say once a year, another could say once every three years, but everyone has their own approach. I do my oil changes every 5k miles, brake fluid every year, coolant every 25k miles, and transmission fluid every 30k miles. I guess that’s normal, but someone will see this and say it’s either too much or too little.

In the end, you are in control of how you take care of your investment. It is good to get information from different people for reference, but ultimately, you decide what is comfortable and correct for your car. There are many knowledgeable people here who can guide you in the right direction, and they do really informative treads, but you take care of the car in your own way don’t take it the wrong way I’m not trying to make it that way.

 

[Evox787]

it is one half liter

Why don’t label it in freedom numbers ! So I don’t need to be converting it.

 

[zumbooruk]

Fucking metric bullshit. I appreciate y’all adding Fahrenheit. Thank U.

metric never made it on the moon. Metric didn’t show Japan the sun (twice) js

I agree, even worse when you grew up in a metric country, and after 45+ years in the US you lost your ability to guesstimate in metric and still have not gained the ability to guesstimate in imperial

on the other hand, at least metric is consistent. 1 ml water is 1 gram and has volume of 1 cubic centimeter, and 1 liter weighs 1kg and fits in a 10cm cube, and I can easily remember 1,000 meters in a KM.

while one US cup is 8 fluid ounces, is not 8oz of weight, it is about 8.34 ounces of water weight and a quart is about 2.1 pounds and I have no idea how many feet in a mile, 5000 something?

very confusing and inconsistent esp to someone with OCD

 

[zumbooruk]

But to my understanding, brake fluid absorbs water regardless, because of the properties contained in the fluid

Correct, hygroscopic by design, but some formulation absorb more water quicker, and some formulations absorb less water and slower.

Water vapor is compressible, not a good thing in brake system, which is why I believe that wet boiling point is an important measure, even if not racing, as it shows performance after exposure to water.

 

[Spart]

Thanks, did not occur to me to check viscosity!

Fuchs Titan DOT 514 LV
Dry Boiling Point: 270°C
Wet Boiling Point: 180°C
Cold viscosity at -40C: 750 mm2/s
Change Interval: 2 years

The numbers you found on Titan DOT 514 LV are actually just the minimum numbers to meet the ISO 4925 Class 7 spec, which is itself a sort of low-viscosity version of the DOT 5.1 spec. Fuchs is weird and doesn't specify the actual numbers, they just say they exceed the spec which is the numbers you have there.

Fuchs also doesn't have a recommended change interval published anywhere that I can find. So that may have been an AI search result leading you astray. Bosch makes a specific claim of three years for ESI6, but the telling thing there is that they also say that ESI6 lasts "50% longer than DOT 4, and 10% longer than DOT 5.1". The obvious implication there is that any DOT 5.1 is going to last longer than a DOT 4 by whatever metric they use to determine longevity.

Generally speaking, most vehicle manufacturers are going to specify a fluid change interval of 2-3 years for DOT 3, and almost universally two years for DOT 4 and DOT 5.1, and their euro equivalents (ISO 4925 Class 4/5-1/6/7.)

I say generally speaking, because there are always standout exceptions with this stuff. For example, Chevrolet recommending five year intervals on certain vehicles.

Every fluid is a little different, but there the big reason a DOT 5.1 has better longevity over DOT 4 is borate ester content.

Generally speaking, DOT 4 is majority glycol ether and minority borate ester, and DOT 5.1 is majority borate ester and minority glycol ether. The exact blend depends on the manufacturer and isn't specified by the standard, but the higher borate ester in a 5.1 blend has two big effects: higher moisture tolerance (better boiling point) and slower degradation when wet, slowing down corrosion.

Those two effects mean that in practice, DOT 5.1 has better longevity than DOT 4 despite the fact that it generally absorbs moisture faster. Hence Bosch's claims about ESI6 and DOT 4/5.1 that I linked to above.

If what you are looking for is a fluid that will last the longest in your application, what you actually need is a reliable way to test the fluid. You can get cheap pen testers that measure conductivity of the fluid and infer moisture content from that measurement, but they can't be fully trusted unless you can either somehow calibrate them, or come to an understanding of how they represent moisture in your specific fluid.

For more on this, see here: https://bobistheoilguy.com/forums/threads/testing-an-inexpensive-brake-fluid-tester-iteq-10.354739/

The general rule of thumb is that 0-3% moisture content is the "OK" range and 3%+ is the "replace" range, however I would note that if you're using a DOT 5.1, waiting for the moisture content to hit 4% isn't a crazy thing to do. It's a different fluid that reacts differently to moisture contamination than DOT 3, and the 3% rule of thumb comes from the DOT 3 days.

For more on this, if you want to really dive deep on this topic, check out the military's brake fluid test results: https://apps.dtic.mil/sti/pdfs/AD1091780.pdf

Another good thing you can do is get test strips, which won't tell you the moisture content, but will tell you the copper content that's indicative of exhausted anti-corrosion additives. This can be a better indication of fluid life than purely relying on a moisture content rule-of-thumb: https://www.amazon.com/Phoenix-Systems-3001-B-Strips-BrakeStrip/dp/B000JFJMGO

Longevity with brake fluid is age, use, and environment dependent rather than strictly mileage dependent, but how things age varies quite a bit depending on the environment and what harsh situations the fluid has been exposed to, and how the fluid stands up to that. Tracking the car, living in a humid climate, parking the car outside overnight rather than garaging - these all degrade brake fluid faster.

There is almost no end to this rabbit hole. My basic advice to people who aren't tracking their cars is to either use a really good DOT 3 if their application calls for it and they don't drive in the mountains or tow (ACDelco DOT 3 and Prestone DOT 3 are good ones) or skip DOT 4 and switch to a good low viscosity DOT 5.1. Fuchs and Bosch are good in that area for daily-driver duty, with Fuchs being more economical and Bosch being a bit more expensive but more readily available.

 

[apl360]

Why don’t label it in freedom numbers ! So I don’t need to be converting it.

Exactly!

 

[apl360]

I agree, even worse when you grew up in a metric country, and after 45+ years in the US you lost your ability to guesstimate in metric and still have not gained the ability to guesstimate in imperial

on the other hand, at least metric is consistent. 1 ml water is 1 gram and has volume of 1 cubic centimeter, and 1 liter weighs 1kg and fits in a 10cm cube, and I can easily remember 1,000 meters in a KM.

while one US cup is 8 fluid ounces, is not 8oz of weight, it is about 8.34 ounces of water weight and a quart is about 2.1 pounds and I have no idea how many feet in a mile, 5000 something?

very confusing and inconsistent esp to someone with OCD

Idgaf whomever has the strongest navy should call what system we should be using dammit

 

[zumbooruk]

Idgaf whomever has the strongest navy should call what system we should be using dammit

As far as I recall, it was indeed British privateers that captured the ship carrying the Metric prototypes from France to Jefferson who was an advocate of the decimal system...

 

[apl360]

As far as I recall, it was indeed British privateers that captured the ship carrying the Metric prototypes from France to Jefferson who was an advocate of the decimal system...

We need to deploy the 5th fleet

 

[tacthecat]

For what it's worth, this is from my research when I was looking for brake fluid.

I evaluated based on dry/web boiling point and hygroscopicity (if that's even a word) judged by manufacturer's recommended change interval, looking for change interval of more than 2 years which is the standard for DOT 5.1)...

FWIW - Honda cautions against using DOT 5
"Brake fluid marked DOT 5 is not compatible with your vehicle's braking system and can cause extensive damage."
May or may not have to deal with sharing a common reservoir with the clutch system

 

[TypeRD]

Alright. Y’all are missing the BIGGEST issue here. Op is asking about “break” fluid. DO NOT confuse this with “brake” fluid. True story : A friend took his car to Firestone once. This was 30 years ago. We were in college. They used break fluid and he ended up in the ditch!

OK, actually I don’t know what they used. But he was on the highway and found he had no brakes. He had to drive his car into the ditch to stop! He got a new car out of it, but his folks decided not to sue since no one was injured or anything. Crazy. Don’t use break fluid.

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