When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The only poetic license I exercised was that it wasn’t one bill.
The described replacements didn’t happen all at once. It took three trips over the course of about 18 months. First was replacing seized rear brake calipers (and of course discs and pads.) Then the clutch went. Then *I* borrowed the vehicle and immediately knew that the brake master was on the way out. Before each of the first two trips my friend called, described the symptoms, and I told him what might be potential causes.
When the brake master was replaced I asked him to see how many brake fluid changes had been done prior to the calipers. And the answer was zero.
He’d always taken this car to the dealer once per year and told them to do the scheduled maintenance. He assumed that he would get what he asked for. After the BMC replacement - I had armed him with knowledge to ask the right questions- they admitted that the brake fluid schedule was two years, that they’d never done it, that it was likely the cause of the recent replacements, and then had the ***** to tell him to pound sand when he wanted some goodwill.
When I write “friend of mine” that is what I mean. Precisely.
Let me guess: you failed remedial reading comprehension class.
I did fail reading lol! I was just joshing at the story because it sounded like a dealer invented story. I didn't mean to offend you. I believe it can happen. It just sounds like a horrible nightmare scenario. I am sorry it happened to a friend. Please accept my appologies!
Not knowing the shelf life of unopened containers myself, and BTW a very good question I decided to reach out to a well known oil & brake fluid manufacturer. The recommendation I received is two year shelf life opened or not from the production date which is (should be stamped ) on the container.
Not knowing the shelf life of unopened containers myself, and BTW a very good question I decided to reach out to a well known oil & brake fluid manufacturer. The recommendation I received is two year shelf life opened or not from the production date which is (should be stamped ) on the container.
So I was buying some brake fluid recently in order to flush a motorcycle clutch and brakes and I was lured into buying a brake fluid moisture tester. I'm wondering if anyone ever uses one of these to monitor their brake fluid performance rather than sticking to the frequent 2 year cycle recommended by Porsche. My 911 brake fluid is about 20 months old and when I tested it the reading was 0 % moisture.
I would not trust a brake fluid tester that register 0% on two-year-old 'installed' brake fluid.
Everything I've ever run across suggests that two-year-old brake fluid should have at least 2% water content.
A couple of years ago I was asked by one of my 928 clients to figure out if there was a DOT4 fluid with a longer recommended service life. I found exactly one: https://www.boschautoparts.com/en/au...i6-brake-fluid
I am also pondering the potential of using some 12 year old ATE DOT4 fluid in an unopened bottle. My research has given me shelf life in quite a range. Some say 2 years. Some say 5. And some say as long as it is in a metal container and unopened there is no shelf life.
There are no date stamps on brake fluid so it is actually impossible to know how old it really is. No one seems to offer any facts on this. So it seems to me that no one really knows for sure and these are all just opinions.
I agree.
Here's my opinion: I'll use brake fluid in unopened containers up to 5-years. I suspect it's still good for a long time after. I'd put it in my cars, but not someone else's.
In the world where expiration dates are a matter of life, death, and liability and thus likely covered by regulation, manufacturers are required to run stability studies. In simple terms, these studies are conducted until either a) periodic testing shows product degradation or b) the pre-determined study end date is met, which ever comes first. I have never heard of a manufacturer that continues a stability study indefinitely so as to determine the *maximum* shelf life of its product.
Why? Well, stability studies consume resources. And at a certain point 'someone' in the decision process says X years is plenty and 'that's all I'm paying for....' One could also think of it as planned obsolesce. Furthermore, how long do you as a manufacturer want to take responsibility for any customer's storage conditions?
Thus, and here's conjecture:
Brake fluid manufactures don't care about shelf stability after two years or whatever number of years the manufacture puts on its bottles or website (if anything) because that's what they decided.
I prefer facts and data versus opinions. If I use my tester on this fluid and it shows 0% moisture, that seems to be a good indicator that the shelf life is not an issue and it can safely be used.
As pointed out above in another post, measurement tools need investigation. Blind trust is not a metrology strategy.
Incidentally I might just change it at 2 years anyway to keep my records up to snuff. Some may wonder why I would even take a chance with 12 year old fluid. Yes it is cheap, but if it is perfectly good, why waste the resources and the albeit small amount of money, and deal with disposal?
I change the brake fluid in our cars that see frequent use every year. Why? Because every year those cars get placed on a stand, wheels off for inside and outside cleaning and waxing, cleaning of brake calipers and coating with CorrosionX, oil and filter change, and whatever other service is scheduled. At that point it takes ~30 minutes to flush the brakes.
Originally Posted by Jack F
Please use the 12 year old brake fluid as a test. Test the moisture. Then add a bit of water and retest. See how much water needs to be added to get it to the 3% on the tester. Could be fun. That was my way of saying don’t use it in your car. It’s probably a $10 bottle.
Seems like a reasonable test protocol. I'd probably let the mixture sit for at least a day after mixing-in water before testing. If, with every water addition, the tester produces the expected results then the tester could be deemed reliable. If not, then either the tester or test protocol sucks.
Originally Posted by Mike Murphy
It’s a good point, given how inexpensive and easy a fluid change is and should cost. I say ‘should’ cost.
Exactly. If you DIY it's a one-time cost of a pressure bleeder (~$100) and then 30 minutes and ~$15 per year per car. (Plus paper towels...)
I think another point is, though, is there any difference between 2 years and 12 years?
Yes. The only 'hard' hydraulic parts (e.g. clutch cylinders, brake masters, calipers, etc) that I have to replace on 928s are those that have a spotty (or no) history of brake fluid flushes. On the MY'90+ 928s with the electro-hydraulically controlled limited slip differentials the only times I've had to send those systems to a rebuilder were for those cars with spotty (or no) history of brake fluid replacement.
One such 928 - no history of flushes - when I and the owner flushed it for the first time in his ownership, we were getting rust particles out of the bleeders for the first two quarts of fluid. I warned him to expect problems.
There's the story of my friend above.
My '91 928 (bought in '97) with 110k-miles still has all of its original 'hard' hydraulic components. All function perfectly. And it's never been more than three years between fluid changes. Which brings us to storage:
Is there a difference to how the car is stored (in a climate controlled garage versus on the city streets)?
I'm sure there is. Brake fluid pulls in moisture through the seals. If your car lives in West Texas where 25% humidity is a muggy day then I would expect brake fluid to last longer.
On the other hand, the typical unheated/uncooled garage with an unsealed concrete floor will have humidity swings. Concrete is porous to moisture unless sealed. In my neck of the woods, garages are often poorly sealed and insulated. In some parts of the country (e.g. Houston where 90% humidity is a dry day...) I wouldn't be surprised if the garage temperature transitions through the dew point with regularity.
Bottom line: think about your own personal storage situation before deciding if you can extend brake fluid changes.
I’d say 2 years could be extended if you don’t track the car, and you store in a garage. Maybe another year or two, but that’s as far as I would go.
If you are tracking your car more than once per year you are probably changing your brake fluid at least once per year. The enemy, on track, is the boiling point of the brake fluid.
However, in terms of off-track service life, rust/corrosion is the enemy.
I'm going to write that again:
In terms of off-track service life, rust/corrosion is the enemy.
And it is the moisture in the brake fluid that accelerates rust/corrosion.
If you turn-over your Porsche before it's 10 years old, then you have a choice:
- Screw the next owner by skimping on brake fluid changes. Or
- Be kind to the next owner.
If you are buying a Porsche, new or used, and intend to keep it. Change your brake fluid every 2 - 3 years or face the really big bills when it's 15 to 20 years old.
Then there those cars purchased with an unknown or incomplete picture of what fluids were changed. That was the case on my car when I bought it in 2017. I therefore changed ALL fluids to set the baseline.
Exactly.
DIY fluid maintenance is, in my not completely uninformed opinion, the cheapest insurance you can buy for your prized 'keepers.'
Last edited by worf928; 06-03-2020 at 10:11 PM.
Reason: typos
It just sounds like a horrible nightmare scenario. I am sorry it happened to a friend.
It was. Doubly-so because one could argue that it was the dealer's fault for not following the recommended maintenance schedule.
My friend is brilliant but holds his cars in the same esteem I do my toaster. He does know they require more maintenance than a toaster. He thought he was doing the 'correct' thing by taking it to the dealer and telling them 'do what's on the recommended schedule.' He has learned his lesson.
With the third failure, it seemed highly likely that lack of fluid changes was the culprit. I was surprised but, not shocked, that the dealer had never changed the brake fluid.
In the Porsche World, it seems that dealers like to 'over-maintain' (and thus profit), whereas in the realm of 'more mundane automotive margues' it seems as if under-maintaining is the norm.
This brings up the last point: Trust but verify.
Please accept my appologies!
Accepted. I don't make $h1+ up. When I do it's either obvious or I write "I'm making this up." I try to ensure that the origin of what I write is clear whether it's first-hand, opinion, guessing, rumor, or conjecture. If it's a story from a friend's niece's brother's mistress's lesbian lover, you'll know it.
I have a fluid tester too, but testing in the reservoir is not where the fluid will fail.
The fluid is stressed in the caliper. The piston seal is where the moisture gets into the system. So even when the fluid tests perfect, I would at least bleed the brakes to get the old fluid out of the calipers. Add fresh fluid to the reservoir. Good to go for a couple more years of daily driving. If tracking, I'd flush brake fluid way more often.
In the old days when mid 60s corvettes had disc brakes with aluminum calipers and pistons. They would corrode due to moisture. So the calipers had to be upgraded with stainless piston sleeves and new pistons. That helped the problem, but you still had to change fluid as now just the pistons get pitted from water intrusion.
I have a fluid tester too, but testing in the reservoir is not where the fluid will fail.
The fluid is stressed in the caliper. The piston seal is where the moisture gets into the system. So even when the fluid tests perfect, I would at least bleed the brakes to get the old fluid out of the calipers. Add fresh fluid to the reservoir. Good to go for a couple more years of daily driving. If tracking, I'd flush brake fluid way more often.
In the old days when mid 60s corvettes had disc brakes with aluminum calipers and pistons. They would corrode due to moisture. So the calipers had to be upgraded with stainless piston sleeves and new pistons. That helped the problem, but you still had to change fluid as now just the pistons get pitted from water intrusion.
I would have thought that the reservoir is the place where moisture is most likely to infuse into the brake fluid. After all, while some moisture might make it past the caliper seals, there is definitely a vent to atmosphere in the reservoir to allow fluid to drhain into the master cylinder as needed.
Also, how much does the humidity in the ambient air affect this change interval. Here in Colorado, relative humidity is typically under 20 percent year-round. I suspect that makes for direr brake fluid than in the deep South.
Here is what I found in the technical data sheet for the popular Ate brand TYP 200 brake fluid (yes, containers have dates on them). Five years sealed container see blue text below. Years ago the containers were not clearly marked but now they are. See photos of backside of container Paragraph 5 and date on front side at bottom 04.2022.
"This product data sheet describes the properties of the ATE DOT 4 TYP 200 brake fluid intended for use as hydraulic fluids in brake and clutch systems of motor vehicles.
This brake fluid for hydraulic brake and clutch systems of motor vehicles exhibits the best capability for water absorption and the highest boiling point reserve of all ATE brake fluids. The composition is governed by the water-binding polyethylene glycol ether boric acid esters and additives specially developed for this high-performance fluid. The wet boiling point has been maximized at approx. 200°C in order to permit long intervals between brake fluid changes and to minimize the risk of vapor lock caused by used, watered brake fluid in heated-up brake calipers after extremely severe braking.
ATE DOT 4 TYP 200 brake fluid meets and even exceeds the requirements of brake fluid standards including FMVSS No. 116 – DOT 4, SAE J1704 and ISO 4925, Class 4.
Shelf life at storage temperatures of –20° C/–4° F to 40° C/104° F: Up to 5 years in the original, factory-sealed packaging.
Product properties:
Condition Homogenous, transparent
Color yellow
Boiling point min. 280° C/536° F
Wet boiling point min. 198° C/388,4° F
Viscosity at –40° C/–40° F max. 1,400 mm²/s
Viscosity at +100° C/212° F 2.2 to 2.8 mm²/s
Water content max. 0.20%
Brake fluid must be replaced regularly. The replacement intervals specified by the vehicle manufacturer must be complied with. The instructions of the vehicle manufacturer with respect to the brake fluid specification must be observed.
A Safety Data Sheet as well as additional information regarding this topic are available under www.ate.de"
Last edited by enthusiast; 01-16-2021 at 03:02 PM.
Reason: photos and more details
I bought one of those $10 meters off Amazon and stuck it in the MC of my '17 C2 today. I believe the reading is 3%.
Is this a "drop everything" and get the fluid changed situation? Or can I go a few more months until it's convenient to get it done? As far as I know, the brake fluid was last changed April of '19, almost two years ago. Does 3% for two year old fluid sound about right?
I did the front pads and rotors a couple weeks ago, and just pushed the pads into the calipers until I could get them on the new rotors, which was basically as far as they would go. So the old fluid got pushed up the lines, possibly into the MC, which I am not thrilled with, obviously. Time was I'd do a simple fluid exchange myself like on my bimmers, but I sold all my maintenance gear, including my Motive Bleeder (we moved into a condo at the time, no place to work on cars. ). I may just let the dealer do this one, since I have a 30K service coming up and it will be in the shop anyway for the plugs.
Last edited by Rich_Jenkins; 02-28-2021 at 07:54 PM.
I wonder if opening the MC and performing a test ends up adding more moisture in an attempt to test the fluid so that you might not need to change it?
Well, I guess that could be...but I always had the impression (valid or not) that brake MCs had a vented cap to allow for the fluid to expand/contract in the master cylinder as the pads wore down. Whether the 991.2 MC is sealed to the atmosphere or not, or has a diaphram isolating the fluid, I'd defer to the experts (I'm not one)...at any rate, I do plan to have the fluid changed at next opportunity.
I bought one of those $10 meters off Amazon and stuck it in the MC of my '17 C2 today. I believe the reading is 3%.
Is this a "drop everything" and get the fluid changed situation? Or can I go a few more months until it's convenient to get it done? As far as I know, the brake fluid was last changed April of '19, almost two years ago. Does 3% for two year old fluid sound about right?
I did the front pads and rotors a couple weeks ago, and just pushed the pads into the calipers until I could get them on the new rotors, which was basically as far as they would go. So the old fluid got pushed up the lines, possibly into the MC, which I am not thrilled with, obviously. Time was I'd do a simple fluid exchange myself like on my bimmers, but I sold all my maintenance gear, including my Motive Bleeder (we moved into a condo at the time, no place to work on cars. ). I may just let the dealer do this one, since I have a 30K service coming up and it will be in the shop anyway for the plugs.
If it's reading 3% in the reservoir I'd want to change that fluid ASAP as chances are the water content in the lines closer to the brake calipers is higher.
Well, I guess that could be...but I always had the impression (valid or not) that brake MCs had a vented cap to allow for the fluid to expand/contract in the master cylinder as the pads wore down. Whether the 991.2 MC is sealed to the atmosphere or not, or has a diaphram isolating the fluid, I'd defer to the experts (I'm not one)...at any rate, I do plan to have the fluid changed at next opportunity.
Reasonable to change for sure. When you get new fluid can you test to see the moisture level. Many would be curious to see what it reads.
Well, I guess that could be...but I always had the impression (valid or not) that brake MCs had a vented cap to allow for the fluid to expand/contract in the master cylinder as the pads wore down. Whether the 991.2 MC is sealed to the atmosphere or not, or has a diaphram isolating the fluid, I'd defer to the experts (I'm not one)...at any rate, I do plan to have the fluid changed at next opportunity.
Your location says Florida so I thinks its safe to assume that your high humidity is a major contributor to the 3%. As already stated you should do a change ASAP. Its a sure bet you would quickly boil your fluid on the track and maybe with aggressive braking on the road. The moisture also causes long term corrosion.
It would be a good scientific experiment to test the moisture content at the calipers and the MC. Until someone does this its just a debate whether opening the MC contributes to the moisture content in a measurable way or microscopic leaks around caliper seals and brake hoses and where the moisture content is higher.
Maybe someone who tracks and changes brake fluid more frequently will do the experiment.
I have a 2016 MB GLC300 that is just off warranty. I plan on checking the moisture content with a tester but probably replace at 1% or worst case 2%.
While most manufacturers still recommend 2 years there are a few that have extended that time frame with moisture testing.
06-03-2020, 05:53 PM
). I may just let the dealer do this one, since I have a 30K service coming up and it will be in the shop anyway for the plugs.
