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Basic parts store fluids are the lowest grade.....
The "odd" lifespan percents for the Bosch fluid is because they consider it done when it can no longer perform to spec. DOT3 also has a higher acceptable % of water contamination vs anything else so "wet" DOT3 actually has more water in it than DOT4 at both being "wet" or in need of replacement.
DOT3 is such a low spec in all aspects that it lasts insanely long in those applications. There is no reason to use it anymore really, everything else is superior in all ways if you aren't buying no name junk. Modern ABS blocks also outright require LV fluids in newer cars
Failure to service is a maintenance issue, even factory, old, DOT4 cars give you 2 years on each change. Thats plenty of time IMO, not worth it to decrease be ABS, VSC etc effectiveness......plus if you are lazy just use a modern fluid that lasts longer than DOT3 anyway.
I think that in their marketing materials Bosch is comparing the DOT 3 and 4 to the minimum boiling points for DOT 5.1, that's the only way it would make sense. Dry DOT 3 has slightly a higher boiling point than wet DOT 5.1 but would drop below the minimum wet standards for 5.1 long before the much lower standards for wet DOT 3, which is what the data for Prestone Max DOT3 would be for. Where have you read DOT3 is allowed more moisture than DOT4? Everything I've ever seen has standards based only on boiling points. DOT has a longer lifespan because in almost all cases it absorbs moisture more slowly. From the link in previous post:
We can see that after 24 hours of humidification the Bosch DOT5.1 (5.1 E) has absorbed 30% more water than the DOT3 fluid. In the corrosion testing it is comparable in many metals but still exhibits higher rates of corrosion against some metals
These would be the only advantages for it. Performance-wise any DOT4 or 5.1 would be superior, but if someone is more concerned about system longevity without regular brake fluid changes than they are about boiling fluid then DOT3 would be a better option for them. Personally, the only time I've experienced brake fade other than bedding in pads was many years ago driving a 10yo Ford van on its original fluid and towing an unbraked trailer with a 4Runner on it down a mountain pass after a hurricane when the main roads were all out, which is not something I hope to ever do again. My new trailer has brakes, so DOT3 meets my needs at this time.
In the most simple terms of why you have a misconception of the rating it's as follows....
In an actual car system every time you use the brakes you are drawing a small volume of moisture into the system. Doesn't matter what fluid you have in the car this volume remains the same, thus ESI6 having the greater capacity for said moisture exposure will last longer before failing spec.
The reason ESI6 is rated as lasting so dramatically longer is because for it to hit the saturation point where it would act as wet dot3 and for corrosion to fall outside of acceptable spec for that fluid is because DOT3 is such a low requirement. Most DOT3s have a joke of an add package that allows them to start corroding the lines etc internally far sooner at lower water saturation levels. ESI6 is able to absorb so much more before reaching this failure point it's about 2x the lifespan.
Your own provided charts prove that it not only can absorb more water when exposed to a worst case scenario but that even then it still provides comparable protection as DOT3. 30% more ability to absorb water and still hit spec seems substantial to me...
In an actual service environment that is semi-sealed like a cars brake system that means the ESI6 has MASSIVELY more leeway in how much water it can absorb and still outperform DOT3. DOT3 exposed to the same service environment simply has way less capacity for water before it fails it own (already low) spec across the board.
Meanwhile the ESI6 is still holding on when massively more contaminated, proving the claims it has superior formulation and lifespan. This isn't even factoring in low temperature pumpability and compatibility with newer systems that DOT3 outright fails.
If the only time you have boiled fluid is bedding I question your bedding procedures as that would require a bleed afterwords. It also indicates to me you have never really driven a car that hard...
I encourage everyone to read the thread from BITOG as it confirms the superiority of Bosch 5.1 over the other options. I'll provide a screenshot of the relevant section however
Brakes are a sealed system, moisture intrusion is not a given when the brakes are pressed depending on seal conditions. Solid butyl rubber, polypropylene, and even viton will let water vapor pass through over time, so much of it is probably a gradual process. 5.1 does not have 30% more ability to absorb water, it has 30% more propensity to absorb water. All wet specs are based on 3.7% water content. All the Dot 4 and 5.1 tested reached that 3.7 saturation point more quickly than the DOT 3. Moisture causes corrosion, which is why almost all Dot 4 & 5.1 exhibited greater propensity for corrosion against almost all metals tested. They make up for this by having a higher boiling point throughout the curve, which is why I said if someone is more concerned about system longevity without regular brake fluid changes than they are about boiling fluid then DOT3 would be a better option for them, and vice versa. OP said he "drives like an old lady" and is worried about actuator lifespan, so he likely falls in the first category, as do I.
Originally Posted by Striker223
If the only time you have boiled fluid is bedding I question your bedding procedures as that would require a bleed afterwords. It also indicates to me you have never really driven a car that hard...
I'm not interested in getting into a dick swinging contest about who drives cars harder. I know how I drive relative to everyone I know and everyone I pass, but I don't drive track and my driving style doesn't involve slamming on the brakes repeatedly to the point of boiling fluid. If someone is regularly boiling fluid on the street, especially without towing, then they probably need to start looking a little further down the road. Brake fade is friction loss from hot pads and is pretty common when bedding in midrange pads, following the pad manufacturers directions to the letter. In these cases, even with the brakes starting to smell and fade and getting extremely hot I don't believe I've ever boiled fluid, which is my point. Bosch seems like a great fluid for anything that gets tracked or needs that viscosity spec. I'm not knocking yours or anyone's choice to use it. Everything in life had tradeoffs and brake fluid is not an exception, and it's not one size fits all.
Brakes are a sealed system, moisture intrusion is not a given when the brakes are pressed depending on seal conditions. Solid butyl rubber, polypropylene, and even viton will let water vapor pass through over time, so much of it is probably a gradual process. 5.1 does not have 30% more ability to absorb water, it has 30% more propensity to absorb water. All wet specs are based on 3.7% water content. All the Dot 4 and 5.1 tested reached that 3.7 saturation point more quickly than the DOT 3. Moisture causes corrosion, which is why almost all Dot 4 & 5.1 exhibited greater propensity for corrosion against almost all metals tested. They make up for this by having a higher boiling point throughout the curve, which is why I said if someone is more concerned about system longevity without regular brake fluid changes than they are about boiling fluid then DOT3 would be a better option for them, and vice versa. OP said he "drives like an old lady" and is worried about actuator lifespan, so he likely falls in the first category, as do I.
I'm not interested in getting into a dick swinging contest about who drives cars harder. I know how I drive relative to everyone I know and everyone I pass, but I don't drive track and my driving style doesn't involve slamming on the brakes repeatedly to the point of boiling fluid. If someone is regularly boiling fluid on the street, especially without towing, then they probably need to start looking a little further down the road. Brake fade is friction loss from hot pads and is pretty common when bedding in midrange pads, following the pad manufacturers directions to the letter. In these cases, even with the brakes starting to smell and fade and getting extremely hot I don't believe I've ever boiled fluid, which is my point. Bosch seems like a great fluid for anything that gets tracked or needs that viscosity spec. I'm not knocking yours or anyone's choice to use it. Everything in life had tradeoffs and brake fluid is not an exception, and it's not one size fits all.
Curious as to what brake brands you bedded that had you overheat them as part of bedding, I've yet to encounter a brand that advocates intentionally overheating till pad fade. Link them if you would, most pads and brands don't even explicitly outline instructions on bedding and brands that do never result in overheating.
Brakes are not a sealed system, the res cap is not airtight at all. Almost all moisture enters though this area, you expose the same amount of water to the fluids and they will both absorb it....one simply does so without as severe of a penalty.
Read what I wrote again, you are failing to understand. Also read the linked threads. Higher spec fluid, and ESI6 in particular lasts longer and has less corrosion risk.
