Brake Fluid Tester temptation

[Pugglt Auld Jock]

We do a "big" supermarket shop roughly every two weeks. Mostly from Aldi but also get some favourites from Lidl - Filtered milk, peppered salami and sweet chilli rice crackers for starters. As there's "heavy" stuff to lug about - like milk etc - and with Mrs J's bad back I tag along to do the heavy lifting. Of course while she's going around with the trolley it leaves me free to take a good look at the "specials" and on this occasion I was unable to resist temptation! https://offers.kd2.org/en/gb/lidl/pkRQj/

It's a resistive type tool and they don't get a particularly good name for accuracy but they are very convenient to use. Only £7.00? Wonder if I can sneak it into the trolley without Mrs J noticing? Wa hey, it's in the shopping bag!

Ok, so what's this all about? Well, as many on here will know very well, conventional brake fluid is hygroscopic which means it absolutely loves water and absorbs it out of the air at any opportunity it gets. - So don't take the top off brake and, clutch fluid reservoirs unless topping up. Yes there's an air hole but you'll let much more air, and so moisture, in if you take the top off - This is unfortunate because temperatures in braking systems can easily exceed the boiling point of water and when water boils it becomes a gas and gasses are compressible! Brakes work because the brake fluid is not compressible so can transmit the movement of the brake pedal to the calipers/cylinders at the wheels. If there's enough water mixed with the fluid - and it doesn't take much - then when it boils and becomes a gas the brake pedal, with almost no prior warning, can go right to the floor and you'll find the brakes will not now slow the vehicle. For this reason most manufacturers recommend flushing through the braking system with fresh fluid every 2 to 3 years. This problem is a most insidious one as the brakes will operate normally until enough heat is generated - maybe by descending a long steep hill with lots of brake use or doing a couple of consecutive very hard stops from high speed perhaps on a motorway in heavy traffic. Of course water in the brake fluid will cause more rapid corrosion of caliper pistons etc too, so it would be very handy to know if your brake fluid has absorbed a potentially dangerous amount of water wouldn't it? Well you can.

There are currently two main types of tester one type actually applies heat to the fluid until it boils the other puts a small electrical current across a carefully calibrated distance between two electrodes and measures the electrical resistance of the fluid between them. The Lidl one I bought - see above - is of the resistive type and I bought it partly because, if it proves to be accurate, it's going to be very quick and easy to use whenever I'm working on one of the family cars. Trouble is there are some claims that this type is not very accurate but I've been looking into this and I think I know why.

There are different specs of brake fluid! Ok, the obvious one is silicon based fluid - DOT5 - which this tester won't work with at all - indeed you wouldn't want to use it with this type of fluid as it doesn't absorb water in the first place (it has other reasons why I wouldn't use it however) so we can forget about it. "Standard" brake fluids are given a DOT number. DOT3 spec used to be very popular in everyday cars but has now been largely superseded by DOT4 which has a higher boiling point. Some manufacturers - my wee Seat Ibiza being one - now recommend DOT4 PLUS (you'll find it labeled as "super" sometimes) which has a higher boiling point again. Then there's DOT5.1 which is yet higher again and mostly used in very high performance or heavy vehicles. By far the most common you'll encounter is DOT4.

Many years ago I decided to buy the boiling point type because of it's greater accuracy and that I was looking after the "family fleet" so could justify the considerably greater cost. I went for the one made by Liquid Levers, just over the water in Fife, and it's been an excellent purchase:

You connect the leads to the car battery and dunk the probe on the bottom of the tool into the brake fluid reservoir until the wee hole in it's side is submerged. Then you press the red button and the element in the probe boils the fluid whereupon a reading is displayed directly on the screen in degrees centigrade. You simply need to compare that reading to the scale on the chart (of which there's a "quick glance" version on the tool:

Calibration of the tool needs to have an eye kept on it but the process is very simple. All you do is to operate the probe in distilled water when you should see 100 C displayed. If it doesn't show this you return it for calibration. So far it's always checked out so I don't know what they would charge for calibration.

The resistive tool:

Takes a triple A battery and is operated by dunking it's probes:

into the fluid and pressing the red button on the handle:

whereupon a series of lights illuminate against the scale indicating the percentage of water in the sample.

Having only bought it this week I haven't actually tried it yet but it seems very simple to operate. My intention is to check with both the older "boiling point tool and the new resistive one and keep a record of results which I'll compare after I've done checks on several of the family cars. Then we'll be able to see how accurate and reliable the new tool is? Bearing in mind that the different specs of fluid exist I'm interested to see the new tool has DOT4 printed on it. I believe it probably won't be so accurate if used on DOT3 or DOT 5.1 and maybe a little less reliable on DOT4 plus? It's going to be interesting to see.

I think the reputation for erroneous/unreliable results which these resistive tools seem to have may be because people don't realize they are only accurate with one DOT spec of fluid - in this case DOT4. As long as it proves to work well on DOT4 that'll do me fine because everything in the family fleet runs DOT4 except the Ibiza - and even that actually has DOT4 in it just now because I recently found out that the garage that did the flush for me back in the spring keeps their pressure bleeder filled with DOT4! This really shouldn't cause any problems but I'll be flushing it through with DOT4 plus next time I service her.

Once I've compiled my results, if there's anything interesting to comment on, I'll come back to this thread with some comment. Don't hold your breath though, might take me a year to get enough results to be meaningful.

 

[Pugglt Auld Jock]

Maybe should mention, by the way and whilst we are discussing this subject, that a very few vehicles use a mineral fluid in their braking systems. A couple I could mention are certain models produced by Citroen and Rolls Royce which use LHM mineral fluid. I believe the hydraulic system used in these older Rolls cars was actually produced under license to Citroen? Anyway, mineral oil of course can't be tested with these testers - and doesn't need to be as it doesn't absorb moisture in the first place! Often, 'specially on newer cars, you'll find a sticker or other notice on the reservoir as to what fluid to use so you know where you stand. Putting a DOT brake fluid in one of these is a very expensively disastrous thing to do! In fact doing it either way, mineral into a DOT system or 'tother way about is disastrous as it will ruin all the seals, ABS unit, and on the Citroen/Rolls the power pumps and suspension too as it runs on the same fluid!

 

[Pugglt Auld Jock]

Another thought I've just had is that, because I'm working with cars I know well and do the services and most of the maintenance on, i know what DOT brake fluid is in them. Diagnosing when fluid is too contaminated becomes difficult if you don't know what fluid you're dealing with. However, as most now run DOT4 you'll not go far wrong assuming that's what's in the reservoir. You'll be very unlucky to stumble across anything with DOT3 in it now a days? and if it's DOT 5.1 the only thing may be that by condemning it on the DOT 4 figures you will just be changing it earlier than you strictly needed to. Or is my reasoning flawed?

 

[vexorg]

Or just change it when it looks cloudy

 

[Pugglt Auld Jock]

Yes, many do that and/or just renew it every 2 years. However many don't. I'm not sure but I think by the time it becomes cloudy it may be quite well contaminated? I've come across the attitude that "Oh it's all a lot of hogwash, I've not changed my brake fluid in years and I've never had the slightest problem". Well they won't as long as the fluid doesn't exceed the boiling point of water will they? and the really nasty thing is that that's only likely to happen in exactly the sort of circumstance when you really really need the brakes to work and many people will drive for years without needing to do a stop of this type. My recollection from working on the shop floor is that a fair number of the vehicles I worked on had pretty dark looking fluid. I always noted this on the job sheet and I know the reception would try to sell a fluid flush to the customer but very few took it up - Probably a good thing for me because neglected cars like that often had seized nipples which invariably snapped off when you tried to loosen them for bleeding!

 

[chris3234]

Yes, many do that and/or just renew it every 2 years. However many don't. I'm not sure but I think by the time it becomes cloudy it may be quite well contaminated? I've come across the attitude that "Oh it's all a lot of hogwash, I've not changed my brake fluid in years and I've never had the slightest problem". Well they won't as long as the fluid doesn't exceed the boiling point of water will they? and the really nasty thing is that that's only likely to happen in exactly the sort of circumstance when you really really need the brakes to work and many people will drive for years without needing to do a stop of this type. My recollection from working on the shop floor is that a fair number of the vehicles I worked on had pretty dark looking fluid. I always noted this on the job sheet and I know the reception would try to sell a fluid flush to the customer but very few took it up - Probably a good thing for me because neglected cars like that often had seized nipples which invariably snapped off when you tried to loosen them for bleeding!

I'd go as far as saying over half the cars in the road never get the fluid changed unless they have has new calipers or brake lines fitted

 

[theoneandonly]

Another mineral fluid user was Audi (100 but not A6) With self leveling suspension it took 5l plus @£10l
As to using the cheap tester Both my UP (68) and Ducato (18) still show ok but skoda (10) says change which i will do.
Will also change the ducato after cam belt as a 4 tonne MH down hill prefer brakes not to have problems.

 

[Pugglt Auld Jock]

Another mineral fluid user was Audi (100 but not A6) With self leveling suspension it took 5l plus @£10l

I meant to say I didn't know that, despite having worked on VAG "stuff" and having several examples in the family. However it's usually been the more budget type vehicles - Fabia, my old Cordoba and the Ibiza. Interesting to know about it so thanks.

 

[portland_bill]

I meant to say I didn't know that, despite having worked on VAG "stuff" and having several examples in the family. However it's usually been the more budget type vehicles - Fabia, my old Cordoba and the Ibiza. Interesting to know about it so thanks.

Have you tested your new toy yet?
I was thinking, put a small amount into an eggcup or similar, from a fresh container, and test it.
Leave it for a few days, and test again.
If possible, leave it outside, under cover, but where it can absorb moisture, and try again.
(Then find it fallen over, and start again)
Maybe add a few drops of water, mix, and test.
Anything else you can think of.

Or ignore this silliness as you have better things to do.

 

[Pugglt Auld Jock]

Have you tested your new toy yet?
I was thinking, put a small amount into an eggcup or similar, from a fresh container, and test it.
Leave it for a few days, and test again.
If possible, leave it outside, under cover, but where it can absorb moisture, and try again.
(Then find it fallen over, and start again)
Maybe add a few drops of water, mix, and test.
Anything else you can think of.

Or ignore this silliness as you have better things to do.

Morning PB. I like the idea of doing that. So far I've only got round to taking it out of it's packaging, inserting the included battery - tested it's voltage first just to be sure - and pressed the button whereupon all the lights lighted in a self test, then extinguish leaving just the green battery light illuminated which I presume means battery is Ok. so all would seem to be working.

I'm in the middle of a small nightmare with my younger boy's builder just now who having, very satisfactorily completed 99% of the extension - bit of "snagging" still to be done - has fallen off his ladder whilst constructing a bespoke staircase on another project. His fall was broken by "bouncing" off some floor joists half way down before completing the fall all the way down into a concrete floored basement! The poor chap has broken his leg in 2 places and done serious damage to his arm too, probably lucky he didn't kill himself. Although the standard of his work has been very good and we are generally more than pleased with what he's built for us, his paperwork is abysmal and this injury is now exacerbating the problem in that Building Control want us to supply certificates for gas, plumbing, fire alarms etc before they will issue a completion certificate and the clock is counting down before we have to restart the application procedure which will involve more site visits etc. I'm trying to contact the electricians and plumbers directly and so far discovered the electrician is away on a project up in Aberdeen and the plumber is not answering his 'phone or emails - Aaaargh!

Maybe a little "workshop therapy" would have a calming effect on me? I've an opened bottle of brake fluid which was used back in the early summer, so seal broken less than 6 months ago, when I was doing yearly service work on the cars, the lid of which was only removed during topping up. I'll try both testers on it. I'm reluctant to buy a new bottle just to do this test though. I'll try the same test on the cars but maybe not today as it's promising heavy rain and it's just "spitting" right now.

Hopefully I'll be back with some results from the opened bottle this afternoon.

 

[theoneandonly]

Perfect candidate for test , perhaps someone with a 20-30year old part used tin and a tester could add in some values.

And then tell us all old stuff ought to be binned and buy a new tin.
Go and clear the shed of anything 10-20-30yrs old. Pick a number or xxx has an unlimited shelf life.

 

[Pugglt Auld Jock]

Ok, just finished "playing" in the garage and I really enjoyed doing that and I'm now nicely destressed!

I found the bottle of Napa DOT4 brake fluid and it's still two thirds full with it's top nice and tightly screwed down I poured some out into the wee container supplied with the Liquid Levers kit (see pictures in my original post at the top of the page) and tried the restive (Lidl Parkside brand) first. To make it work you press the red button and it briefly illuminates all the LEDs then settles back to just illuminating the green bottom "battery ok" LED:

This means it's "on" and ready to go (It'll "auto off" after a wee while if you don't use it or you can switch it off by pressing the red button again). So, with it now on, you immerse the probes in the fluid and right away it illuminated the first light only:

Which the scale lists as ok (below 1% water content). Two LEDs lit would indicate 2%, 3 gives 3% and 4 gives 4% Above 2 and you need to think about changing.

Then I repeated the test with the Liquid Levers boiling point tester. which has a very handy "how to" guide on the back:

so you really can't go wrong with this simple to use tester. The most important thing to remember is not to press the actuator (red) button when the tip is not immersed in fluid or you risk frying the heating element!

First you connect the power leads to the battery - this turns it on, there's no switch - I don't think they are "protected" so be careful to connect Pos to Pos and Neg to Neg. Having done that the tool tells you it's ready to go:

Next you dunk the probe in and out of the fluid a few times to get a representative fluid sample into it and to stabilize the sensor temperature. Then, making sure the probe is immersed above the level of the bleed holes you press the big red button for a few seconds. The machine is operating - heating the element - when the display starts displaying random shapes:



You can release the "big red button" once it starts to do this. the random flashing slows down and when it's "happy" it displays a steady reading:

The manufacturer recommends taking at least two readings for maximum accuracy so I usually take 3 and find the first reading is often marginally low. In this case the second and third attempts produced:

and I find this difference representative of other readings I've taken so not really significant.

The minimum reading for DOT4 is 155 degrees C so this fluid is in excellent usable condition - Visually it looks nice and clear too.

So far the below 1% and the boiling point reading of 243C seems to be consistent - great! Just for reference the max reading the tool can give is quoted to be 272C but I've never seen it getting near that.

So, emboldened by this outcome, and as it's not raining yet, even the slight drizzle has stopped, I thought I'd check the cars.

Becky the Panda first. She was bled out with the same Napa fluid I've just been testing around Easter time? when the rear brake cylinders were renewed. The fronts were not bled at that time but the fluid in the reservoir, master cylinder and rear system will all be new at that time. Possibly some cross contamination from the old fluid in the front may have occurred so the outcome will be interesting (note to self, must bleed the calipers before long.)

Very pleasing to see the resistive tester returned a less than 1% result with the boiling point tester showing 213C:



I think this is probably the expected comparative result? 213 degrees is still a lot above the 155 degrees boiling point at which renewal is recommended for this DOT4 fluid so I'm happy with this outcome both in terms of how the fluid is aging and in terms of the expected reading on the resistive tester.

Then I thought, Ok, go for it boy, let's check Twinkle (the Ibiza). Her fluid was not changed by me. Back around March of this year I let our local VAG indy do a cam belt on her and service the aircon. So while she was in I asked for the brake fluid to be flushed through with new fluid too. so it's probably not NAPA fluid but I know it's DOT4 because I asked. Which disappointed me slightly because it should have been DOT4 plus, but it'll be OK and I'll bleed it through with the "proper" stuff next big service. The good thing, for the purposes of this investigation, is that I know it's DOT4 in the system right now.

I won't go through it "blow by blow" because the procedure is the same as for Becky. The results were:



but the resistive tester still showed just one LED lit - so less than 1% water.

I'm slightly suspicious of this resistive reading. The lowest acceptable reading for DOT4 is 155C and for DOT4 Plus (or Super some call it) is 180C so at 188C I'd have thought it would be on the cusp of illuminating the second LED? But then this resistive tester is calibrated for DOT4 so it's presumably going to fail it at around a reading of 155C. which I'm guessing will be the third LED (of the four possible indicating LEDs) what I don't know is what temperatures the various LEDs illuminate at.

Anyway, interesting results? Looks like the fluid in the bottle is bearing up well and can be safely used for top ups. Becky, who had her fluid renewed as I detailed above so I know it's been thoroughly flushed through the reservoir, master cyl and rear system is showing results you would expect. However I'm a wee bit suspicious as to just how thorough a job the garage did on Twinkle. Even accepting they used DOT4, when it should have been DOT4 plus, I would have expected the readings to have been a wee bit better. Also the fluid is darker looking than Becky's and there is a very small sign of black deposit in the filter insert of the master cylinder reservoir - where you top it up. I'm not so sure they did a very comprehensive flush through so I'll be doing it again myself soon. I want to replace the DOT4 with 4 plus anyway.

By the way, I tested each system and the bottle sample with the resistive tester first just in case the local boiling of the fluid caused by the Liquid Levers tester reduced the water content in the sample. Also I powered it from my large jump start battery which I know is in very good order and showing 12.6 volts open circuit at this time so there could be no variable introduced due to differing voltage levels in the vehicle batteries. Although actually I don't think this is a factor as all it has to do is heat the coil up 'till the sample boils.

One point from the Liquid Levers instruction sheet is that they warn against the possibility that top up fluid may have been added recently to the reservoir of which you may not be aware. Of course this would give a far better result than is actually the case because the tool will be measuring the new fluid which was recently added. They recommend that if there is any suspicion that this may be the case then to take a fluid sample from a front caliper so you are definitely testing a representative sample. Another reason why doing your own maintenance is a bonus, as you'll know if you've added fluid!

So there you are, food for thought? I'll be continuing to use both testers on the "family fleet" when possible to build up a results data base. I'm feeling much more trusting of the Liquid Levers tester at this time, but then I am used to using it. I'd like to see at what point the resistive tester starts illuminating it's "Fail" LEDs and I'm only going to get this by using it on a range of vehicles which I'm also testing with the boiling point tester. So far so good though?

 

[portland_bill]

Thanks Jock. Interesting, and good to see that the Lidl tester seems adequate.

 

[Pugglt Auld Jock]

Thanks Jock. Interesting, and good to see that the Lidl tester seems adequate.

Thanks PB. Yes it's looking promising. It's pretty obvious it's going to be a much less "definitive" tool but probably we don't need the exactitude of the boiling point tool for everyday use where vehicle service history is known? It's big drawback is that I suspect it's outcomes are only really reliable when used with DOT4 fluid, which is fine if you can be absolutely sure it's DOT4 you are testing. So fine for the sort of thing I'm using it for and probably for a lot of driveway greasemonkeys who are doing their own maintenance. Question is, could this type be relied on in a general service workshop?

 

[theoneandonly]

Thanks jock ,
now the next test as per portland bills idea test samples after day ,week of being open to air

 

[eeeno]

Lidls have that same brake fluid tester here too but I was hasty and ordered one for two coins and half from Aliexpress.

Sure it only looks good, but for my surprise IT IS NOT CALIBRATED properly. It says water's water, all leds illuminate when even testing a small drop of water. One could think it works, but NO. Six years old used flushed DOT4 fluid only lights up one (battery ok) led and when testing from the brake liquid reservoir on a car the result is same - only one led lights up. I wonder why chinese can get away with a fraud like this. So I speculate that they're selling items that failed quality checks on Aliexpress.

Testing brake fluid with multimeter

There's a site instructing to use a multimeter for brake fluid test to measure the strength of the chemical reaction in the brake system. So the multimeter is set to measure DC voltage - red probe to the reservoir and push black one to the side of the master cylinder firmly. The value of 0.3V would indicate 3% water content and immediate need to change the fluid. My result on 3 years old DOT4 was 0,04V which means that the liquid still OK. I understand that this measurement needs to be repeated after a year for a comparison for it to be useful at all.

One thing to note is that DOT4 corrodes plastics, so don't immerse the plastic parts of the multimeter probes or testers into the liquid. The chinese ones have disintegrated after few tests according to the feedback the seller's received. Now the seller asks me to give five star praise for them and they refund the few coins.

I think five years service interval to be good for brake liquid and many new cars don't get that done at all and are fine even after ten years with old DOT4. Sure it'd be better to change it more frequently...

 

[Pugglt Auld Jock]

Ok. After eeeno's comments above - about a completely different brand of tester - I'm going to try what has been suggested above by "theoneandonly" and, I think someone else?

Going to put a sample of fluid in an open topped container and place it just inside the garage door where it'll be in the draught from outside. Without a top on I expect it'll absorb moisture much more quickly than it would in a typical master cylinder so it'll be interesting to see how fast it degrades. I'll be testing it with both tools. The Boiling Point tool I know works so it'll be interesting to keep comparing it's readings to the resistive tool and see just how accurate (or not) it really is.

I'm expecting this to take some time before meaningful results are obtained but I'll repost in this thread when I've something meaningful.

PS eeeno, interesting to read about the plastic disintegrating. The Lidl instructions advise washing the end of the tool in water after every use and, with brake fluid being hygroscopic, I'd guess this removes all traces. I've done it with mine and it certainly looks very clean. From now on though I think I'm going to only submerge the actual probes in the fluid

 

[portland_bill]

Ok. After eeeno's comments above - about a completely different brand of tester - I'm going to try what has been suggested above by "theoneandonly" and, I think someone else?

Going to put a sample of fluid in an open topped container and place it just inside the garage door where it'll be in the draught from outside. Without a top on I expect it'll absorb moisture much more quickly than it would in a typical master cylinder so it'll be interesting to see how fast it degrades. I'll be testing it with both tools. The Boiling Point tool I know works so it'll be interesting to keep comparing it's readings to the resistive tool and see just how accurate (or not) it really is.

I'm expecting this to take some time before meaningful results are obtained but I'll repost in this thread when I've something meaningful.

PS eeeno, interesting to read about the plastic disintegrating. The Lidl instructions advise washing the end of the tool in water after every use and, with brake fluid being hygroscopic, I'd guess this removes all traces. I've done it with mine and it certainly looks very clean. From now on though I think I'm going to only submerge the actual probes in the fluid

Brake fluid is often sold in plastic containers, and of course most reservoirs are plastic, so some grades of plastic must be ok.
I've often wondered why brake fluid reservoirs are always so opaque, for what is a light coloured liquid, when coolant tanks, under pressure, are seemingly made of lighter grade stuff. Perhaps the corrosive qualities of the brake fluid are significant.

 

[theoneandonly]

I didn't get instructions with my cheap ebay tester. After use I just put the cap back on and it welded itself on. Washing after use is a good idea

 

[Pugglt Auld Jock]

Brake fluid is often sold in plastic containers, and of course most reservoirs are plastic, so some grades of plastic must be ok.
I've often wondered why brake fluid reservoirs are always so opaque, for what is a light coloured liquid, when coolant tanks, under pressure, are seemingly made of lighter grade stuff. Perhaps the corrosive qualities of the brake fluid are significant.

I meant to say the NAPA container is plastic, indistinguishable from a one litre engine or gearbox oil container.