Reusing brake fluid used for bleeding brakes?

Webley1991 · Feb 17, 2019

Every time I have bled brakes on a vehicle I have thought that I have ended up wasting more brake fluid than I needed to.

I did this recently and poured it from the jar back into the bottles and put the caps back on tight. I marked the used bottles of fluid and put them in a box in the corner of the workshop as not to accidentally add them back into the system.

I am aware that it absorbs moisture from the air once the containers are opened.

If it is put back into a sealed container and was then filtered before re-use to remove any possible contamination, why can't it be reused? Wouldn't any moisture evaporate once the brakes had been up to temperature enough times?

Every time I do that job I end up thinking I am throwing good money away.

Disco1BFG · Feb 17, 2019

I'd suggest you change the way you bleed the brakes ... unless you're changing the fluid, you shouldn't need to use "lots"

Whilst some of the water might evaporate from the hot end of the braking system - it's not enough to make it worth re-using dot 4. The cost of calipers (etc) is far greater than the fluid ....

Our local motor factors sells 5 ltrs of Dot 4 for about £10 .... So, IMHO, it's a single use product.

Best thing to do, is to use silicon fluid after a major rebuild. This doesn't absorb water, but it does NOT mix with Dot 4 either, so the system needs to be spotlessly clean and devoid of all other fluids before you can use it ... ( quite a job then

).

However, given the cost of silicon fluid, and the ease of changing the fluid in the first place - i shall be using dot 4, and changing every two years, as per recommendations.

payydg · Feb 17, 2019

To keep things simple I only use fresh Dot 4 and regularly check with a moisture meter. Given that it doesn't cost that much and you don't really waste huge amounts when you bleed the brakes I don't see the point in re-using.

Moron · Feb 17, 2019

Put it like this............would you use second hand brake pads ?

Webley1991 · Feb 17, 2019

The job I did was replacing all four wheel cylinders on my Series 3 SWB.

I ended up going through nearly two litres of fresh fluid trying and ultimately failing to get all of the air out. I could tell when the old (since I did the job last time) stuff was gone from the system as the colour in the bleed pipe changed.

I buy it in 500ml bottles from my local motor factors. They cost about £3.50 each, but they allow returns for a cash refund on any that are unopened. That way I don't have an opened part used 5 litre container sitting around to go to waste.

Dippypud · Feb 17, 2019

Webley1991 said:
The job I did was replacing all four wheel cylinders on my Series 3 SWB.

I ended up going through nearly two litres of fresh fluid trying and ultimately failing to get all of the air out. I could tell when the old (since I did the job last time) stuff was gone from the system as the colour in the bleed pipe changed.

I buy it in 500ml bottles from my local motor factors. They cost about £3.50 each, but they allow returns for a cash refund on any that are unopened. That way I don't have an opened part used 5 litre container sitting around to go to waste.

Unless you have mates and you're both going to use a fair amount doing a major brake service or fluid change ... as most vehicles also use the fluid for clutch too

blue beasty · Feb 17, 2019

Old dot 4 works fine in my set up

Dippypud · Feb 17, 2019

blue beasty said:
Old dot 4 works fine in my set up

View attachment 170185

Have you given up on throwing the dog out the back whilst still on the chain ?

blue beasty · Feb 17, 2019

Dippypud said:
Have you given up on throwing the dog out the back whilst still on the chain ?

He too fat and just rolls along behind.

Besides it nearly woke him up the last time

flat · Feb 17, 2019

I used the remains of an opened, and less than week old, bottle of dot 4 in my clutch to get me out of a bind and home.

Treat it as single use containers and accept you will bin some. It’s not worth the risk on safety critical components.

I was told that the problem isn’t so much the water in the fluid but rather the corrosion and air locks that it will cause in the brake system leading to early failure. Don’t know how true that is but my brakes are very important to me so I use fresh unopened fluid every single time.

Old fluid makes a great paint stripper by the way lol

Al2O3 · Feb 17, 2019

flat said:
I used the remains of an opened, and less than week old, bottle of dot 4 in my clutch to get me out of a bind and home.

Treat it as single use containers and accept you will bin some. It’s not worth the risk on safety critical components.

I was told that the problem isn’t so much the star in the fluid but rather the corrosion that it will cause in the brake system leading to early failure. Don’t know how true that is but my takes are very important to me so I use fresh unopened fluid every single time.

Old fluid makes a great paint stripper by the way lol

Are you on your phone there, matey? Looks like pre-emptive text has changed a couple of key words there. iPhone or iPad I’m guessing

blue beasty said:
Old dot 4 works fine in my set up

View attachment 170185

Generating a bit of heat there, BB

Oh and your lovely pooch wouldn’t be that round if you weren’t over feeding him

brian47 · Feb 17, 2019

Webley1991 said:
I am aware that it absorbs moisture from the air once the containers are opened. Wouldn't any moisture evaporate once the brakes had been up to temperature enough times?

Disco1BFG said:
Whilst some of the water might evaporate from the hot end of the braking system - it's not enough to make it worth re-using dot 4. The cost of calipers (etc) is far greater than the fluid .....

For any moisture to evaporate off, it must have somewhere to evaporate to.
In the braking system the moisture is sealed in and as the brakes warm up, yes the heat will cause the moisture to form water vapour, but it has nowhere to go. So it just forms little bubbles in the fluid. Bubbles which can lead to brake fade, sponginess and possible total failure.

flat · Feb 17, 2019

Al2O3 said:
Are you on your phone there, matey? Looks like pre-emptive text has changed a couple of key words there. iPhone or iPad I’m guessing

Generating a bit of heat there, BB
Oh and your lovely pooch wouldn’t be that round if you weren’t over feeding him

Err yeah on a phone lol!!

Al2O3 · Feb 17, 2019

flat said:
Err yeah on a phone lol!!

Guessing you didn’t mean to say ‘the star’ and ‘my takes’.

flat · Feb 18, 2019

Al2O3 said:
Guessing you didn’t mean to say ‘the star’ and ‘my takes’.

Yeah edited it now lol

Al2O3 · Feb 18, 2019

flat said:
Yeah edited it now lol

No need really, cos you could see what you meant.
Anyway, you didn't say if it was an iPhone. I'm only curious, cos it bugs me how apple think they know what you mean better than you do. There's something subtly worse about their system.

flat · Feb 18, 2019

Al2O3 said:
No need really, cos you could see what you meant.
Anyway, you didn't say if it was an iPhone. I'm only curious, cos it bugs me how apple think they know what you mean better than you do. There's something subtly worse about their system.

Yes iPhone, and autocorrect irritates the sh1t out of me tbh. Half the typos are because the keyboard is ‘touch’ on the screen. I have the same issue with my work android tbh.

Maybe it’s fat thumbs :/

Al2O3 · Feb 18, 2019

flat said:
Yes iPhone, and autocorrect irritates the sh1t out of me tbh. Half the typos are because the keyboard is ‘touch’ on the screen. I have the same issue with my work android tbh.

Maybe it’s fat thumbs :/

Aye, might be fat thumbs

I find Android pre-emptive text far less domineering.

Disco1BFG · Feb 18, 2019

Al2O3 said:
I find Android pre-emptive text far less domineering.

Agreed - Daughter and I sometimes play a game where we send each other texts of the predicted words - she's on crapple, I'm on android .....

Some of the stuff we send each other is proper weird, often funny, but the crapple texts are more bonkers

headintheclouds · Feb 19, 2019

Moron said:
Put it like this............would you use second hand brake pads ?

Plenty of us have. When we buy a second hand car. I had a nearly lethal experience many rears as a result. I bought a classic car that had been standing on grass for a few years. Welded up the underside, freed up the seized bits and took it for a spin and all was well. Some weeks later I was driving along and hit the brakes. Pedal straight to the floor. Pumped pedal and to massive relief I got brakes on about 4th pump.

Long & short was that water had got between friction material and back of pad. Either rust or ice had expanded and severed the friction material from backing. Friction material exits stage left + trousers in need of urgent laundry.

Learn from this, people!

Reusing brake fluid used for bleeding brakes?

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