OV9

Posted: **Fri Jul 04, 2025 1:43 pm**

I bought a brake fluid tester recently, one of those pen type devices that tells you how much water is in the brake fluid. I tested the Jaguar and it was 1.1% so well within spec.

But then I got to thinking, brake fluid isn't cycled around the system, it's just there. So although there may be only 1% in the reservoir does that mean at the caliper end it could be wildly different? Why would it be? Where does the water come from?

Should I throw it all away and start again and other existential questions.

Posted: **Fri Jul 04, 2025 1:50 pm**

£20 for race fluid plus £20 for a pressure bleeder and an hour spent will change it yourself. Its not worth fucking about with.

Posted: **Fri Jul 04, 2025 2:12 pm**

Good reddit post about the topic. I understand that water content levels at the calipers are likely to be higher than those measured at the master cylinder / resevoir, but I've not seen anything that explains why that would be.....

Posted: **Fri Jul 04, 2025 2:22 pm**

I would have thought there would be more water at the reservoir end because there’s usually a tiny bleed hole to stop the reservoir pressurising, so would be exposed to the atmosphere.

Then again, you always top up at the reservoir so that’s where the freshest fluid is going to be.

I always loosen the bleed nipple if I have to retract the calliper for any reason anyway. Many mechanics don’t or say it’s not necessary but in my head it’s good practise because the bleed nipple is less likely to seize is opens once in a while, you push out some of the oldest most heat cycled fluid and your putting less stress the wrong way on the various seals in the system.

Posted: **Fri Jul 04, 2025 3:07 pm**

scotta wrote: Fri Jul 04, 2025 1:50 pm £20 for race fluid plus £20 for a pressure bleeder and an hour spent will change it yourself. Its not worth fucking about with.

This.

Although a decent bleeder seems to be about £50, but I may just do this. I was curious about the mechanics of hydroscopics tho

Posted: **Fri Jul 04, 2025 3:31 pm**

integrale_evo wrote: Fri Jul 04, 2025 2:22 pm I would have thought there would be more water at the reservoir end because there’s usually a tiny bleed hole to stop the reservoir pressurising, so would be exposed to the atmosphere.

Then again, you always top up at the reservoir so that’s where the freshest fluid is going to be.

I always loosen the bleed nipple if I have to retract the calliper for any reason anyway. Many mechanics don’t or say it’s not necessary but in my head it’s good practise because the bleed nipple is less likely to seize is opens once in a while, you push out some of the oldest most heat cycled fluid and your putting less stress the wrong way on the various seals in the system.

This is what mechanics do when they’ve had to drill out their own bleed nipples or had a master cylinder spill it’s guys during a brake job.

Stuff sitting and never being moved is what causes most problems.

As for where the water sits, I always understood it that the water settles in the bottom of the system. Which is why you can get rusty marks on the inside of your pistons and calipers.

Dave!

Posted: **Fri Jul 04, 2025 3:40 pm**

tim wrote: Fri Jul 04, 2025 3:07 pm
scotta wrote: Fri Jul 04, 2025 1:50 pm £20 for race fluid plus £20 for a pressure bleeder and an hour spent will change it yourself. Its not worth fucking about with.
This.

Although a decent bleeder seems to be about £50, but I may just do this. I was curious about the mechanics of hydroscopics tho

@scotta has the Sealey VS820 pressure unit, and also the VS0212 collector bottle. (We used it on Elise & Evora before Anglesey last year).

I was impressed (so much so that I may just get one myself next time), and initially thought the collector bottle was a bit of an extravagance when I always used a jam jar back in the day, buuuut - it is of course graduated so you can see read exactly how much fluid you've pushed through each time - so it was actually an extremely useful element - particularly when you have multi-pot calipers and want to ensure both sides are sorted

(I therefore had to eat my hat

).

Posted: **Fri Jul 04, 2025 3:53 pm**

That was the one I was looking at

Posted: **Fri Jul 04, 2025 3:58 pm**

I have the same bleeder. The kit comes with one cap and I don’t recall which cars it works with. They sell additional caps for other manufacturers for a silly price though.

Posted: **Fri Jul 04, 2025 4:21 pm**

I’ve had an ez-bleed which uses a spare tyre for pressure for about 25 years, it came with a load of adapters but the standard cap it comes with has fitted every car I’ve tried to use it on so I’d assume they are fairly well standardised.

Posted: **Fri Jul 04, 2025 4:24 pm**

integrale_evo wrote: Fri Jul 04, 2025 4:21 pm I’ve had an ez-bleed which uses a spare tyre for pressure for about 25 years, it came with a load of adapters but the standard cap it comes with has fitted every car I’ve tried to use it on so I’d assume they are fairly well standardised.

Well, if the cap fits......

Posted: **Fri Jul 04, 2025 4:34 pm**

integrale_evo wrote: Fri Jul 04, 2025 4:21 pm I’ve had an ez-bleed which uses a spare tyre for pressure for about 25 years, it came with a load of adapters but the standard cap it comes with has fitted every car I’ve tried to use it on so I’d assume they are fairly well standardised.

Harry & I are twins.

Posted: **Sat Jul 05, 2025 7:28 am**

I tested my gf’s lad’s 2015 Fiesta last night. 4% lol. Probably never been changed.

Will add brake fluid to the list of service jobs we need to do in the coming week and get one of those sealey jobbies ordered.

Posted: **Sat Jul 05, 2025 8:18 am**

So I can't find any reliable info on what the brake fluid capacity is of a 2015 Mk7 Fiesta. Haynes manual doesn't mention it either. Would a typical 500ml bottle be enough do we reckon for a full flush? Feels like not but it's been a long time since I've done this myself.

Posted: **Sat Jul 05, 2025 8:21 am**

Id be more tempted to get a litre and flush 200ml ish through each corner as it’s probably not been done in a while

Posted: **Mon Jul 07, 2025 9:24 am**

So it appears Ford use a non-standard brake fluid reservoir cap so that Sealey jobbie isn't likely to work without additional faffery.

I'm wondering if I can use the suction pump I bought to suck the oil out of my jag and pull the fluid through via the bleed nipples tho? Seems like it would be ok as long as the fluid level doesn't dip too far.

Posted: **Mon Jul 07, 2025 10:09 am**

Yes, should be fine. You can buy suction bleeders. Like you say, just go slowly and make sure the reservoir is kept brimmed.

I’d be tempted to just use enough pressure to pull a small stream of fluid and slowly press and release the pedal at the same time to help push it through the system and allow you to keep an eye on the level.

Posted: **Mon Jul 07, 2025 11:41 pm**

Sundayjumper wrote: Fri Jul 04, 2025 4:34 pm
integrale_evo wrote: Fri Jul 04, 2025 4:21 pm I’ve had an ez-bleed which uses a spare tyre for pressure for about 25 years, it came with a load of adapters but the standard cap it comes with has fitted every car I’ve tried to use it on so I’d assume they are fairly well standardised.
Harry & I are twins.

This is the £20 option I was talking about. I also have one of these in addition to the more expensive one with the pump that Mik mentioned.

You can buy a universal thing for them that connects to the resovoiur with a chain for non standard bottles. I used that on a Honda CRV.

https://ebay.us/m/LrCr0A

Posted: **Sat Aug 16, 2025 2:39 pm**

Mito Man wrote: Fri Jul 04, 2025 3:58 pm I have the same bleeder. The kit comes with one cap and I don’t recall which cars it works with. They sell additional caps for other manufacturers for a silly price though.

Doesn’t work with ‘E’ prefix BMWs either

Posted: **Sat Aug 16, 2025 6:18 pm**

Works fine on e30, e36, e46 and e53

OV9

Testing Brake Fluid

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