Brake fluid change - is flushing the system necessary?

[Jusitne]

Hi everyone,

My fiesta eco boost is getting its first brake fluid change this week.  Timewise the change is after Fords recommended period of 2 years - the car is 3.5 years old.  It’s booked in at the Ford dealership.  Should I expect them to flush the brake system or bleed it only?  Can a flush be done as the fluid reserve serves the brakes and the clutch?

Is there anything else I should ask the garage to check re the brakes / clutch when getting the work done?

[Comares2001]

They wont flush it . They just bleed out and replace fluid ,but only about 75% of it gets replaced.

[isetta]

If the car was 10 years old and never had a fluid change I doubt if there would be any ill effect. I know the theory of why it needs changing but in the real world it does not seem to matter imo

[TomsFocus]

They won't flush it, but all of the fluid should be replaced.  Basically you suck the fluid through until it changes colour (topping up the reservoir all the time).  The lighter coloured fluid is the new stuff so it should all be replaced by that point.  Takes very little time with the modern vacuum bleeders they use now.  

I also don't agree that there's no difference on 10 year old fluid...brakes start to feel very spongy once you've boiled it at the caliper end a few times.  Contaminated fluid is also an MOT fail now btw.

[Jusitne]

At service it was tested and boiled at 320 degrees.  I’m assuming this is Fahrenheit which is 160 Celsius.  At 160C temperature Ive been told it needs changing.  

It boiled at 220C when tested over a year ago.

[isetta]

Do they really take a sample out and test it’s boiling point? Can anyone who works at a garage confirm this? Is it a special purpose made thing? As opposed to a saucepan on hob with thermometer stuck in it

[TomsFocus]

54 minutes ago, isetta said:

Do they really take a sample out and test it’s boiling point? Can anyone who works at a garage confirm this? Is it a special purpose made thing? As opposed to a saucepan on hob with thermometer stuck in it

There is a special tool for this purpose yes.  https://www.lasertools.co.uk/product/6802

 

[Jusitne]

So at 160degrees Celsius is it time to get it changed?

[TomsFocus]

7 minutes ago, Jusitne said:

So at 160degrees Celsius is it time to get it changed?

Yeah, 160c is pretty low tbh, anything under 180c would be considered bad.  I'm surprised it's dropped so much over a year though, I'd check the seal on the reservoir cap tbh!

[Piston Head]

Brake fluid absorps moisture which in turn lowers the boiling point. Boiling water produces steam = vapour in the fluid so hence the spongy pedal

Not ideal

 

[Eric Bloodaxe]

2 hours ago, isetta said:

Do they really take a sample out and test it’s boiling point? 

The local garage where I get the Mrs's car serviced demonstrated this to me last time I was in. They do this at every service and change fluid as they deem necessary rather than at a fixed time/mileage interval, subject to there being no contamination etc.

I think the absolute minimum boiling point to meet the standard of the commonly used DOT 4 fluid is 155C, but they would change it well above that.

[Jusitne]

The time period from dropping from 220 to 160 was 18 months.  It could be that the readings have not been 100% accurate but either way its time to get it changed.  Fluid is 3.5 years old so is probably overdue its change plus (Ford recommend every two years

[Jusitne]

They have 320 degrees on service record - this must be Fahrenheit.  It cant be Celsius.      

[Jusitne]

So I’ve converted 320 degrees from Fahrenheit to Celsius which comes out at 160 degrees.

 

[Eric Bloodaxe]

2 hours ago, Jusitne said:

So I’ve converted 320 degrees from Fahrenheit to Celsius which comes out at 160 degrees.

Surprised that they're using Fahrenheit these days, thought it was only me who did that!😀

This can be a bit of a confusing subject as there are two figures quoted for brake fluid, "dry" and "wet". The "dry" figure is for new unused fluid as sealed in the container. The "wet" figure is for in-service fluid (ie in the reservoir of our cars) that will have picked up a bit of moisture (I think the standard is based on the assumption of something like 3.5% water content) and this figure is a lot lower than the "dry" figure. For the common DOT 4 fluid, the minimum figures are 230 "dry" and 155 "wet", both centigrade.

Fluid can pick up moisture remarkably quickly if exposed to air, eg if a cap is left loose, there is a tiny leak somewhere, or through natural permeability of flexible brake/clutch hoses and other seals. So a good idea to have it checked regularly.

[Jusitne]

Update - i took car back to Ford dealership and they re-tested boiling point - still 320 degrees Fahrenheit.  I asked if this means i need it changed - tbh they were useless saying it depended upon the water content and I could only find this out by getting it tested at a chemist.  This from a Ford trained technician.  He then said if the nipples break i would need new cylinders costing £100 each!

 

So at 3.5 years old, no brake fluid change as yet, and boiling at 320 degrees Fahrenheit / 160 degrees Celsius do i need this changed?

[Bobr]

I'm not really bothered about the boiling points etc. although it is interesting.   I get my brake fluid changed every two years regardless.   For what it costs, is it worth not having good brakes when you really need them?

[Tizer]

Years ago I suffered a Brake Pedal to the Floor incident in an old car because one of my brakes was binding and the heat boiled the fluid (that probably had never been changed) and caused an airlock.

It was a frightening experience and needless to say I have changed my Brake Fluid every since then. 

[Eric Bloodaxe]

6 hours ago, Jusitne said:

So at 3.5 years old, no brake fluid change as yet, and boiling at 320 degrees Fahrenheit / 160 degrees Celsius do i need this changed?

As above - 160C is almost at the limit, so yes.

[isetta]

but then if the bleed nipples snap you will be kicking yourself and possibly wish you had not done it. soaking bleed nipples in something like wd40 a few times on the days leading up to them being undone might help.  hopefully on a car that age they won't be corroded too badly but the fact they mentioned it makes me wonder if they know from experience it is a problem on cars of that age.

"I asked if this means i need it changed - tbh they were useless saying it depended upon the water content and I could only find this out by getting it tested at a chemist". this does sound a daft comment. the boiling point is lowered due to the water content so testing the boiling point is a measure of how much water there is in it. the higher the water content, the lower the boiling point.

I can honestly say that if it was my car I would not do it. But I can not possibly recommend that to any one else. I am not giving you advice I am just saying honestly what I would do. If I drive normally the parts of my braking system that have the fluid in are never going to get anywhere near 160 degrees centigrade. If I was using the car for racing it would be a different matter.   As I say - I am not giving you advice, this is just my thoughts on my own car. 

 

[isetta]

if I did have it done I would be tempted to test boil some of the brake fluid now and afterwards to see what the difference is. need a small metal container on my gas hob with a thermometer in it. I know it would not be all that easy to do.

[AndyDC]

I agree, and after decades of working on classic cars etc I finally found a need to do a complete flush.

I had the displeasure of working on a neighbour's 18yr old Nissan recently, probably never had a change of fluid. We had to remove and strip a caliper, so lost a fair bit of fluid (a caiiper's worth), so it had new added. What came out looked like the colour of used cooking oil in a fish shop. We topped up, and had a problematic 3 months subsequently where the system kept generating air (no fluid gets out, air forms but increases the fluid level in the reservoir) and finally solved it when we did a complete flush including a vacuum bleeder. So, the old fluid was probably nowhere near as high as 160 deg boiling point but we'd have never known that unless he did a long journey at high speed (he normally does c5miles at up to 30mph) and actaully heated the brakes a lot more than normal.

 

So, once on a car where the fluid is probably c18yr old. perhaps flush at 10 years then to be safe. 

 

[Jusitne]

thank you for the replies.  The brakes do seem ok and I drive fairly lightly no the brakes - 10 miles to work each day through country roads.

Has anyone had a problem with bleed nipples snapping during brake fluid change on a 3.5 year old car?

[Eric Bloodaxe]

52 minutes ago, Jusitne said:

Has anyone had a problem with bleed nipples snapping during brake fluid change on a 3.5 year old car?

Not once in nearly 50 years, either at a garage or when doing the job myself on cars much older than that.

 

[Tizer]

1 hour ago, Jusitne said:

Has anyone had a problem with bleed nipples snapping during brake fluid change on a 3.5 year old car?

No, they are more likely to get mangled if cheap spanners are used on them, but that should not happen on a young car like your one.