car brake fluid top up

nottingham13

I need to top up my car brake fluid, i have some in the garage opened but i dont know how old it is. Could be 5 years old or even older.

I read my manual and it says that you should only use new fluid to top up

Any ideas whether using old brake fluid is ok?

molerat

Brake fluid absorbs water so an opened container is likely to be contaminated after that amount of time.

colino

Brake fluid is cheap, if you have the slightest hesitation, throw it away. Do you need to top it up? The pistons/cylinders will naturally move out as pads and shoes wear out and the reservoir level will drop. As long as there hasn't been a sudden drop (you've got a leak!) and the level remains above the minimum mark, there isn't a problem. Otherwise, when you move the pistons/cylinders back when you replace the pads/shoes with new ones, you'll either have to draw off the excess from the reservoir, or as a lot of people do, just let it overflow and then wonder why its gone rusty below the reservoir.

AdrianC

Unless it's a brand new bottle, still sealed - don't use it. Bin it.

How long since the fluid in the car was last changed? It should be changed every two years.
Why do you need to top it up? What's leaking?

Strider590

Its more of an advisory, if the fluid has been kept in a sealed container and is still watery in colour, then it should be perfectly ok.

As brake fluid ages and absorbs mousture, its colour changes to appear much darker.

At the end of the day, when its poured into the car its exposed to air, when the fluid cap is closed half the reservoir is filled with air and after 2/3/4/5 years its no different at all to the same fluid kept in a plastic container.

Strider590

colino wrote: »

Brake fluid is cheap, if you have the slightest hesitation, throw it away. Do you need to top it up? The pistons/cylinders will naturally move out as pads and shoes wear out and the reservoir level will drop. As long as there hasn't been a sudden drop (you've got a leak!) and the level remains above the minimum mark, there isn't a problem. Otherwise, when you move the pistons/cylinders back when you replace the pads/shoes with new ones, you'll either have to draw off the excess from the reservoir, or as a lot of people do, just let it overflow and then wonder why its gone rusty below the reservoir.

You'd want to open the bleed nipples when opening out the pistons, pushing fluid back could flip the seals in the master cylinder or in some cases damage the ABS.

Better to open the system and do a full bleed as part of changing the pads/discs.

I suspect a lot of the horror stories come about from people trying skimp on fluid bleeding when changing pads/etc.

facade

Check the brake pads.
"Modern" cars dispensed with the wear sensors in the brakepads and rely on the drop in brake fluid making the warning lamp come on when the pads are nearly worn out.

If they are fine, check for leaks, as the brake fluid doesn't disappear, and if there are none, as Colino says remember that any fluid added because of pad wear will have to come out when new pads are fitted.

arcon5

Strider590 wrote: »

You'd want to open the bleed nipples when opening out the pistons, pushing fluid back could flip the seals in the master cylinder or in some cases damage the ABS.

Better to open the system and do a full bleed as part of changing the pads/discs.

I suspect a lot of the horror stories come about from people trying skimp on fluid bleeding when changing pads/etc.

Yes in theory it's a possibility! In reality though it's very uncommon. You will find 99/100 garages and DIYers alike will just push to piston back and drain if necessary.

colino

I've never flipped the seals on any car, not even the allegedly notorious v/x ones, and have never heard first-hand of anyone who has. It's from the same chapter as ruining ally cylinder heads changing the spark plugs or tearing the centres out of alloy wheels by over-torqueing them. While technically possible, you'd have to have no mechanical sympathy and be incredibly inept to do so.
Generally suggested to the layman to keep them paying techs to do simple jobs on their cars.

AdrianC

colino wrote: »

It's from the same chapter as ruining ally cylinder heads changing the spark plugs

No, that one's real and frequent. If it wasn't, then the helicoil or timesert would be fairly pointless and redundant inventions.

colino

Spark plug threads are wrecked by incompetent gorillas over-tightening them, or the clueless who cross-thread them, but keep on graunching them up, and they'd do so on any material.
The myth with ally heads is that you have to leave them to the end of the service, sprinkle them with holy water and say a prayer to Z.A.D. or the threads will melt.
No fun anymore with better engines, long-life plugs and not having to meddle with old Fiestas!