More than a quarter of cars in the UK could be using ineffective brake fluid, increasing the likelihood of an accident

Research has suggested that more than a quarter of all the cars in the UK have defective brake fluid.

Now you, like us, might raise an eyebrow at that statement. The research, carried out for Cosan Lubricants’ Mobil Car Care range, however, bears some consideration.

Brake fluid is hygroscopic, meaning that it absorbs water from the atmosphere. Over time this reduces its effectiveness by lowering its boiling point.

When the fluid boils, vapour is produced – which is compressible – resulting in a soft brake pedal and a decreased, or non-existent, braking effort.

Cosan says that brake fluid, which has a typical boiling point of between 230-260 degrees C when new, becomes all but useless once it boils below 180deg.

Brake fluid expert Alba Diagnostic concurs, suggesting that brake fluid should be changed when its boiling point is down to 200deg C — and it’s below this figure that the research suggests more than a quarter of all cars will boil their fluid.

After all, how many of us are particularly attentive as to what goes into our brake fluid reservoirs? We may intermittently check the levels, but few of us are likely to go any further.

Many of us use whatever brake fluid tends to be handy — which might be a contaminated bottle that’s been on the shelf for a while. That’s assuming, of course, that the fluid has even been changed in recent history.

Mike Bewsey, of Cosan Lubricants, said: "Many drivers mistakenly believe that if their car has passed its MOT, all of the lubricants and chemicals within it are up to scratch.

"The only way to check the quality of brake fluid is to test its boiling point temperature. As that is not part of the MOT, the onus is clearly on motorists to ensure that their car is safe."

So if you’ve only been intermittently checking your brake fluid’s levels, or don’t know when it was last refreshed, perhaps it’s time to consider a change. After all, for £100 including labour, it’s cheap insurance.

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20 August 2014
I suspect that very very few accidents are the result of cars boiling their brake fluid. This is only likely to occur during repeated heavy use of the brakes, or during long hill descents - and Britain isn't a very mountainous country. If there was evidence that this was happening, I'm sure that a brake fluid test would be introduced as part of the MOT.
I suspect that the bigger problem may be caused by sticking brake caliper pistons as a result of corrosion, which would be picked up during the annual test. Another issue is that while many motorists pay dealers for brake fluid replacement during routine servicing, there is no easy way to check that the job has been done.

20 August 2014
why would this be particularly "dangerous", bar the most extreme of cases:

The brake fluid's job is to transmit the pedal effort to the disk via the calliper. Surely, in the event of a potential crash (or where maximal braking effort is required), if you can still generate enough force through the pedal / fluid to activate the ABS, then the brake fluid has done its job and isn't the "weak link" in the chain - tyre grip is.

I suppose the caveat here is on a long decent where a car with "bad" fluid is more likely to have less effective brakes, but as I'd wager the vast majority of motoring is either city driving of motorway based, I think this has probably been overblown a little.

That said I've ordered a fluid testing kit now as I've got a new car and want to check it!

20 August 2014
It could almost be that with all the companies mentioned, and the subject matter so flimsy, that this is a covert advert for the brakefluid servicing companies and suppliers? Or maybe I'm far too cynical.

20 August 2014
Of all the cars I've owned over the past 30 years, only TWO have had a brake fluid change, neither of them requested by me. The Merc had it changed as it was part of a fixed price service (the cheapest quote for it's 2nd service was an eye watering £580 - a fluid change for the brakes and a change of underpants for me £580 for a 1.8 C-Class!). The other change was part of replacing a faulty ABS sensor on my Golf. As I drove out the garage I felt the brakes a little spongy but thought nothing much of it. Several miles later and my brakes failed - luckily there were no other vehicles around at the time. The garage hadn't bleed the brakes properly which I guess is another downside of car maintenance - "if it ain't broke..." Not saying I'd never have a brake fluid change, but every 2 years is simply ridiculous. If it was dangerous, then it would be part of MOT and manufacturers would insist on it rather than recommend it. By the way, in all those 30 years of owning a car I have NEVER heard of anyone having an accident because their brake fluid wasn't up to the job.

20 August 2014
I note that the "research" has been carried out by a company with a vested interest in selling us more brake fluid.


I'm a disillusioned former Citroëniste.

20 August 2014
The issue with water contaminated brake fluid is it rusts out the ABS pump. Few in the UK will overheat their brakes unless they are an utter headcase, or driving a 44 ton truck.

The number of cars I see with mismatched part worns on (With 2mm on one side and 7 mm on the other on an axle!)= a real danger when it rains or snows.

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