brake fluid tester. are they accurate and how to

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i bought one of the brake fluid testers off of AMAZON. I tested the crv and sub which has under one year fluid. tested the bmw that has not been changed for 10. on the sub and crv they show 1% . odd to me seeing the fluid in both was under a year. maybe because they live outside might be a factor in the 1%.

what was also odd is the bmw also showed 1% but its been garaged all of it life

also what is the correct way to use it. some say just need to immerse the probes in the fluid.some say it must be immersed till it touche the plastic end . doing one or the other gets diffenrt results

https://www.amazon.com/KINGBOLEN-Brake-L...#productDetails
 
Originally Posted By: Trav
Mix a small amount of water with some brake fluid in a jar, shake it and test.

I you could also do the same with a multimeter. See the change in resistance while adding a certain % of water (distilled, not to increase conductivity with dissolved solids). Compare results.
 
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Originally Posted By: Trav
Mix a small amount of water with some brake fluid in a jar, shake it and test.



LOL, just don't shake any brake fluid you intent to use in the car! shaken fluid has air bubbles!
 
been checking quite a few cars and have not found a 4% yet. 1-2 % . i put the probes in straight water and it lighted up all the lights.
 
Interesting post. Maybe none of the tested fluids had more than minimal amts of water?

Ford, some years ago, tested brake fluid in junked cars at salvage yards and found little water in the fluid. Perhaps your instrument is trying to tell you that?
 
Originally Posted By: Dyusik
Originally Posted By: Trav
Mix a small amount of water with some brake fluid in a jar, shake it and test.

I you could also do the same with a multimeter. See the change in resistance while adding a certain % of water (distilled, not to increase conductivity with dissolved solids). Compare results.


I'm not sure I really understand this story.

What you say seems reasonable, if your meter is sensitive enough, but other sources found on the nyet often refer to testing the conductivity of the fluid (the inverse of the resistance, so still reasonable), but then go on to measure voltage, which isn't a directly related unit.

The procedure generally seems to involve measuring a potential difference (voltage) between the fluid in the reservoir and the vehicle earth, so perhaps its actually measuring galvanic corrosion which conductivity of the fluid allows. IIRC 0.3V is the suggested maximum.

There seem to be a lot of uncertainties in this procedure, including the metallic makeup of the car and your immersed meter electrode, and it seems it couldn't be used to test fluid in the bottle since in that situation there are no different metals involved.
 
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I have tested the same fluid with both a brake fluid tester and multi meter many times - I've never seen fluid with 300mv pass on the fluid tester...and fluid that passes read low on the multi meter. It works...you can do your own tests of course. I don't test new fluid in the bottle of course, as you say we are looking at electrolisis, galvanic action, what ever you want to call it, but corrosion involves electricity.
 
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Originally Posted By: Silk
I have tested the same fluid with both a brake fluid tester and multi meter many times - I've never seen fluid with 300mv pass on the fluid tester...and fluid that passes read low on the multi meter. It works...you can do your own tests of course. I don't test new fluid in the bottle of course, as you say we are looking at electrolisis, galvanic action, what ever you want to call it, but corrosion involves electricity.


OK, if that's your experience, that's useful and relevent info, BUT that isn't the same procedure as the post I was responding to, which talks about measuring the conductivity/resistance of the fluid.

If THAT procedure works (I havn't tried either, though I have tried a voltage check for coolant) then it seems to have some advantages.

It seems to have fewer variables, it should be possible to test in a bottle/tube rather than just on the car, and it should be possible to calibrate it by adding water, which you probably wouldn't want to do on the car.
 
I think the resistance thing is just someone getting it wrong. I haven't tried it, but I think just adding water isn't going to give an accurate result either, like condensation in oil, just adding water to engine oil isn't going to create acids, it needs heat and some time to get working. Same with brake fluid, the damaging stuff takes time in the system to get working. You can do the same with coolant...it's time in the system that gives voltage.
 
I don't know about that tester but if I test brake fluid in the bottle that has had the cap loose for a long time it shows a percentage of moisture.
The fluid was never in a brake system just the original plastic bottle. time for an experiment eh.
 
Originally Posted By: Silk
I think the resistance thing is just someone getting it wrong. I haven't tried it, but I think just adding water isn't going to give an accurate result either, like condensation in oil, just adding water to engine oil isn't going to create acids, it needs heat and some time to get working. Same with brake fluid, the damaging stuff takes time in the system to get working. You can do the same with coolant...it's time in the system that gives voltage.


That was my best guess, but it'd be good to be wrong on this one.
 
Originally Posted By: Silk
I have tested the same fluid with both a brake fluid tester and multi meter many times - I've never seen fluid with 300mv pass on the fluid tester...and fluid that passes read low on the multi meter. It works...you can do your own tests of course. I don't test new fluid in the bottle of course, as you say we are looking at electrolisis, galvanic action, what ever you want to call it, but corrosion involves electricity.


I'm a little confused what you are measuring with the multimeter. Is it measuring fluid conductivity resulting from copper leaching out of brake lines into the brake fluid (increasing its conductivity), or water content?
 
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