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ENV6 Brake Fluid

GrahamR

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Hi all,

Has anyone used Bosch ENV6 brake fluid in their 'Cruisers?
A little light googling seems suggest that it replaces pretty much everything (DOT 3, 4, & 5.1) and out performs them all.

ENV6
Wet: 185 °C
Dry: 270 °C
Viscosity: 670 mm²/s

DOT 5.1
Wet: 180 °C
Dry: 260 °C
Viscosity: 900 mm²/s

I've got to have the ABS motor overhauled so will need the whole ABS unit out, might replace a few dodgy looking lines as well and I want to flush everything through after the motor is back.
It's got DOT 4 in it now which I'm keen to get rid of as there seems to be a fair number of comments about it being bad for seals or something.

Just thought I'd check with you wise folk before I go do something daft!

Thanks,
G
 

uHu

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I would go with Toyota 5.1. Guaranteed compatible with all seals and other brake components.
If you go ENV6 - I'll check with you in 2-3 years, and then maybe switch next time.
 

Beastrider

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Hello Graham,
DOT 3/4/5.1 refers to sets of minimum performance standards laid down by the DOT (US Department of Transportation). They are all based on similar chemistry and can be mixed. The increasing number indicates progressively higher standards - most importantly the wet boiling points.
As far as can see, ENV6 is nothing special - it exceeds the minimum standards, yes, but every other manufacturer does as well - they have to in order to sell it.
In my view, stick to what DOT standard the manual says, choose a good brand of fluid and change it every 2 years. (I have a 90 series which says DOT 3, I expect your manual probably says 3 or 4). If the manual says DOT 3 or4, it won’t harm your seals - they were designed for it.
If you expect your brakes to be heavily used and get very hot (eg. Long descents, heavy loads, riding the brakes), then just change the fluid more often so that it’s less degraded towards the wet boiling point.
Absolutely avoid DOT 5 (which is a completely different chemistry to the others).
 

GrahamR

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Thanks for info and feedback, much appreciated, handbook says DOT 3. I'll run with DOT 5.1. Good advice on regular changes, no heavy use (well, apart from a smoking hot descent of Porlock Hill last year!). I gather from various sources that Dot 5.1 requires earlier replacement than Dot 4 which requires earlier replacment than Dot 3.
 

Beastrider

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Hi - I wouldn’t agree with the earlier replacement comment - if anything, it’s the opposite way around.
The higher number fluids have been specifically developed to improve their initial properties and maintain them for longer. But all these fluids degrade as they absorb moisture over time, so require periodic replacement - 2 years is fine, but sooner is always better, whichever fluid you choose.
DOT5.1 will be fine - make sure it’s 5.1 and not 5
The best fluid is new fluid.
 

Towpack

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I pit Dot 5 in a bike years ago and had the pre flush the system, much easier on a bike obviously, as it was silicone based and would not mix with anything else. The benefits were much higher boiling point, not hydroscopic and lasts virtually forever.
 
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GrahamR

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It was my understanding that the higher the DOT number, the more hygroscopic, thus would absorb water faster necessitating more frequent changes. Is this not the case? The DOT 5.1 performance starts high, but would drop faster with age than DOT 3. Will aim for 2 year max replacement regardless,I'm just curious if I'm getting my facts wrong!

Will indeed avoid silicone based DOT 5!
 

Beastrider

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No, it’s not the case. DOT 5.1 starts with a higher dry boiling point than 4 and 3 and degrades more slowly than 4 and 3, so its wet boiling point remains higher too - much higher than 3. I use 4 because it’s perfectly adequate for these vehicles in normal conditions and I change it regularly. But 5.1 is fine.

DOT 5 is silicone based, as you say, and is incompatible with the ‘normal’ brake fluids. It has the advantages that Towpack mentioned plus won’t damage paintwork if you’re careless and splash some. However, it’s more compressible (spongey pedal), not good in ABS systems and can affect seal function. Ask yourself why virtually no OEMs use it - it’s not just because of cost - it’s because it’s simply not as good.

Strange as it may sound, being hygroscopic is an advantage for a brake system fluid because the performance of the fluid degrades slowly and predictably. When water gets into non-hygroscopic fluids, it remains as a separate bead of water. If that water finds it’s way to the caliper, when the caliper gets hot, you have a fluid boiling point of exactly 100degC - which is worse than any of the proper brake fluids, even when they are severely degraded. This isn’t just theory. I have witnessed it during an investigation into a road traffic collision where a backhoe loader (with a mineral oil brake fluid - non-hygroscopic) collided with a passenger car. Water was found in the brake line at the wheel cylinder and it had boiled following a hill descent, resulting in loss of braking function.
I’ll get off my soapbox now but it is a serious subject. I’ll stick with DOT 3/4/5.1 brake fluids.
 

Beastrider

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Just after writing my rant, I noticed a 2010 thread “Brake fluid explained”. Says much the same as I did. Have a read there too.
 

GrahamR

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Thank you for setting the record straight, much appreciated!
 
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