No, it's not OK to test at the reservoir. You are deluding yourself that reservoir fluif is the same as the fluid im the calipers and ABS block. Will your cheapie tester tell you anything about loss of corrosion inhibitor, copper content, viscosity, particulates?

 

You could always bleed some fluid out at a wheel bleed nipple to test that.
Don't forget to top up after with fresh fluid for whatever volume you bled out to test!

 

What is a good home DIY brake fluid tester?

Seeing EV's don't actually need regular dealership service. I would prefer to take it to change brake fluid only when needed. Every 2 years is way too often.

Is a cheapo pen tester like this one reliable enough?

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If I know the brake fluid has never been topped up, is it okay to test at reservoir?

Brake fluid circulates very slowly around the circuit but the laws of physics still apply and diffusion still occurs, as well as a bit of turbulent mixing. It does this on a much smaller timescale than water absorption does. So there is a theoretical possibility that it's worse in the calipers but the reality is that water vapour tends to enter via the reservoir, so where would you think it's worse?

Test it at the reservoir, it's fine. But I would advise cleaning out and servicing your rear brakes every couple of years anyway to stop them corroding to failure. They get less use than they are designed for on a bev.

 

Not true!

 

Please state what you consider untrue and your experience or evidence for traversing my opinion.

 

What's the driving force for diffusion from say right rear caliper to the master cylinder. Brownian motion????. Numbers please seeing that physics has been invoked. Does this cover transport of wear particulates. Please add a note how / of theory matches reality. Otherwise stop the delusion.

 

How do you think wear particulates at the bottom of the caliper get pushed out of the top of the caliper when the hose with fresh fluid goes in the top?

Unless you pop the piston out, you're never going to get at particulates that aren't in suspension.

As I said before on this subject, I changed the rear calipers on my Espace and the whole of the reservoir was filled with fresh from reservoir to rear. The bleed broke on the front so I did not flush those. Within 1,000 miles the reservoir had gone dirty with fluid from the front calipers.

Tell me how this could happen and I will answer your questions.

 

....... so...... is the cheapo test pen good okay?

Are other changes in brake fluid (loss of corrosion inhibitor, copper content, viscosity, particulates ) as serious as water contamination? I thought water contamination is usually the first sign of brake fluid needing to be changed.

 

The other changes all affect the longevity and reliability of the very expensive ABS block and the functionality of the ESP and ABS systems which requires clean in spec viscosity to function correctly. This is no the same as vehicles from 20 years ago.

There is a certain poster on this forum who a.n. recommends sloppy maintenance:, take those recommendations with care.

 

Personally I don't test the brake fluid at all. I just change it every two years. It's not a difficult task. Takes about an hour and a tenners worth of brake fluid. If I couldn't do it myself I would pay a garage to do it. What price do you put on peace of mind?

 

No need to have the main dealer change brake fluid, this is not part of the EV system so provided your local mechanic doesn't panic at EV'S coming in its not a problem.

 

If you have a Renault Zoe then the cost replacing the brake fluid ( every 4 years) is not cheap and costs around £250 as the Battery under the car has to be locked out so it can be worked on.
but this method seems to only apply to the Renault Zoe.

 

3 years is adequate and basically changing to compensate for moisture absorbtion. On my bikes, where the reservoir is visible whenever you ride, the change in colour from pale straw to brown is obvious as the fluid gets older and soaks up the water. The fluid is cheap and it's an easy DIY job (especially if you have kids available to pump the pedal).

 

VW say first change at 3 years, then every 2 years. It is cheaper and easier to change fluid than ABS unit!!

 

What is the official way to replace the fluid? I.e. how would a garage do it? Do you open up each calliper bleed in turn and pump through a certain amount of fluid? How much?

I have been bleeding through an amount every time I have the wheel off for brake pad checking. But maybe I have not done the rear wheels for a while.

I have one of those pens and it is telling me my fluid is too damp even though it looks perfectly good/clean in colour. Whether it's accurate I couldn't say.

PS The pen is quite a good way to detect damp walls even though it does not have the sharp points of the proper one to spike the wall.

 

The official way (at least for the Ampera\Volt) is via a dealer, who uses a computer to plug in and actuate the valves in the ABS to ensure all the fluid is replaced.

 

Some things baffle me.
It's a few quid every couple of years. Why wouldn't you just swap it?
This is like walking more slowly to save wear on shoes or sleeping for an hour less each night to save on mattress use.
Rather than chasing after testers, testing it (which also unseals the system while you're doing it allowing moisture to be absorbed) and still having to swap it at some point anyway, why not spend the extra hour at work every couple of years and just get it done?
Long term it's far less stress and you know the bits in the braking system you can't see are looked after as well as possible. Is that not worth the difference of £5-£10 a year?

 

Some things baffle me.
It's a few quid every couple of years. Why wouldn't you just swap it?
This is like walking more slowly to save wear on shoes or sleeping for an hour less each night to save on mattress use.
Rather than chasing after testers, testing it (which also unseals the system while you're doing it allowing moisture to be absorbed) and still having to swap it at some point anyway, why not spend the extra hour at work every couple of years and just get it done?
Long term it's far less stress and you know the bits in the braking system you can't see are looked after as well as possible. Is that not worth the difference of £5-£10 a year?

Why generate waste unnecessarily?

Every car wears differently, every brake fluid will have different contamination at 2 years point. Manufacturer recommendation tend to be very cautious, because it costs them nothing while gets dealerships more profit.

Having said that, I think I'll get it changed during every other MOT.
I originally thought testing just involves taking the cap off the brake reservoir and poke the tester pen in. Quick minute job while topping up windscreen fluid.

 

I never understood why DOT 5 silicon fluid didn't become standard. It doesn't absorb water so should never need to be changed.

The cynic in me thinks it would remove another regular task for the garages to charge for...

 

I never understood why DOT 5 silicon fluid didn't become standard. It doesn't absorb water so should never need to be changed.

The cynic in me thinks it would remove another regular task for the garages to charge for...

It was impossible to service. All that happened was that water settled to the lower parts of the system and could not be extracted.
By water diffusing into the fluid, it was then easy to get out .. just swap the fluid out ...

There is no 'good' or 'bad', there is a spectrum of boiling temperatures which is very gradually lowered as water builds in the system.

If you don't drive like a looney then it's unlikely you'd even notice you had 100% water in there!!! Especially with an EV with less mechanical braking forces.