Test brake fluid with multimeter

[core-aggie]

Curious if anyone in here does this :

You can get a pretty good ballpark of the "moisture content" of the brake fluid in an automobile using a multimeter.
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Open the hood, unscrew the brake fluid fill cap, set the multimeter to DC Volts (12 is fine).
Place the red probe in the fluid, and place the black probe to the master cylinder body - unpainted portion.
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Let the multimeter settle down a few seconds .... if the readout is 0.3V or higher, it's time to flush-n-fill !!!
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Anyone do this with a bike ?
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Explained here ...
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https://autoedu.info/en/auto-mechanic/brakes/hydraulic-braking-system/testing-brake-fluid-1/
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Example video:

 

[Willsmotorcycle]

I'm due for a change, I'll test it before and after.

 

[Larry Fine]

Open the hood, unscrew the brake fluid fill cap, set the multimeter to DC Volts (12 is fine).
Place the red probe in the fluid, and place the black probe to the master cylinder body - unpainted portion.

That makes no sense. Where would the voltage come from?

I could see measuring resistance to determine water content.

 

[Andrew Shadow]

That makes no sense. Where would the voltage come from?

I could see measuring resistance to determine water content.

Fluid turns acidic over time and the chemical reaction generates voltage.

The same test has long been used to determine when antifreeze needs to be flushed.

 

[Larry Fine]

 

[red one]

Never heard of that. But my motorcycle mechanic had this thing with a probe and when he stuck it into the brake reservoir all the leds turned red indicating the fluid was bad.

 

[Mellow]

Never heard of that. But my motorcycle mechanic had this thing with a probe and when he stuck it into the brake reservoir all the leds turned red indicating the fluid was bad.

https://www.amazon.com/‎KINGBOLEN-Indicators-Automotive-Accessories-Diagnostic/dp/B09YRL2HKS/ref=sr_1_1?keywords=brake+fluid+tester&qid=1676629349&refinements=p_89:KINGBOLEN&rnid=2528832011&s=automotive&sr=1-1

 

[klaproth]

I have one of the brake fluid testers like the amazon one. Works very well. On the bikes, I just change it every two years, no need to check it. I do check it on my 4 wheel vehicles.

 

[Mr ed]

this is news to me. I've got to try this on my truck and cars then the 13.

 

[Obo]

Guess there's no need to use the 9v battery lick test then to check it, not that you should be licking brake fluid.

I used to be addicted to drinking brake fluid, but I found I could stop whenever I wanted.

 

[SMSW]

That makes no sense. Where would the voltage come from?
I could see measuring resistance to determine water content.

I agree.

Fluid turns acidic over time and the chemical reaction generates voltage.

The same test has long been used to determine when antifreeze needs to be flushed.

I looked on Amazon and found most of the anti freeze testers work on density (several little balls floating type) or refraction of a sample of the AF. The linked tester, and all the other testers that came up in a quick, non thorough search were resistance types, with 2 electrodes about 6mm or 1/4" apart.

If there is galvanic action generating a voltage between the Anti Freeze and the engine block, you can expect galvanic corrosion. Using the resistance setting on a multi meter and checking the resistance between the fluid and the block is going to be much the same as using a dedicated tester with the mentioned two probes molded into a wand. I would think using the probe would generate more accurate results, especially if you changed the ground point each time you tested.

 

[Andrew Shadow]

Testing the antifreeze with a voltmeter is not to determine its density, or its ability to resist freezing or boiling. A traditional tester is needed for this.

This test is nothing new, it has been around for years. I was taught to do this test by the GM training centre way back in the eighties. I think that anything under .5 volts was acceptable, but that is from memory of a long time ago, so it needs to be verified.

Measuring the voltage is an indication of the condition of the additives used to prevent electrolysis and corrosion due to galvanic chemical reaction. As the additives deteriorate the chemical reactions that they inhibit increase, and so does the voltage produced by those chemical reactions. Because there is a correlation between the level of voltage present and the condition of these inhibitors, the voltage present can be used to determine if the antifreeze needs to be changed because the additives are no longer providing effective protection.

You can find testing antifreeze with a voltmeter all over the internet.

 

[core-aggie]

Okay, I thought I'd get things started off with real world examples. Just walked in from the garage and have a couple readings for two of our cages, with brief history. I'd say the reading pretty much coincide with the "life" of the fluid for each !!

#1... The first photo is of the Jeep Wrangler. I did a complete front brake replacement (rotors, calipers, hoses, pads), and complete flush of fluid, front and rear, just shy of a year ago ... reading 0.121

#2 ... Second photo shows readout for the GLK350 - I did front rotors and pads, and flushed all around just shy of three years ago ... reading 0.265.
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[oude geit]

A potential to ground from a grounded fluid. Its a negative reading meaning the potential is less than zero. You using snake oil in them brakes....

 

[core-aggie]

A potential to ground from a grounded fluid. Its a negative reading meaning the potential is less than zero. You using snake oil in them brakes....

Interesting... I didn't notice that ... I bought that multimeter not long ago and have only used it a couple times previous.

Am I doing something wrong or maybe I have a rwong setting ? It's a fairly recent newfangled automagic meter that doesn't require much "manual" setup.

 

[STFlips]

Most multimeters are notoriously inaccurate at very low voltages in DC auto range, use the millivolt scale.

 

[Willsmotorcycle]

I had to go out on the internet and do some searching on this, searching is not as useful as it use to be, galvanic reaction seems to be what everyone is claiming.

I'm no smart guy, what are the two metals in my plastic brake fluid reservoir?

 

[STFlips]

Good question, I can only assume it is through the fluid back to a caliper that is grounded. Just a guess, somebody smarter clue us in.

 

[Andrew Shadow]

I'm no smart guy, what are the two metals in my plastic brake fluid reservoir?

Because the fluid in the reservoir is not segregated from the fluid in the rest of the system, I don't think that what the reservoir is made of matters. Whatever chemical reactions are happening in the system will eventually make their way to the reservoir as well. The reading is an indication of the condition of the brake fluid in the system, not just the fluid in the reservoir.

 

[core-aggie]

I had to go out on the internet and do some searching on this, searching is not as useful as it use to be, galvanic reaction seems to be what everyone is claiming.

I'm no smart guy, what are the two metals in my plastic brake fluid reservoir?

My post #1 includes a link to the Automotive Edu. site that briefly explains it - might have missed it.