JW911

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. According to the instructions, anything less than 3% indicates no need for a flush at this time. So by the time 24 months arrives I will check it again but it will most likely still read 0% or perhaps 1-2%. Just looking for opinions and curious if anyone else uses one of these meters to monitor their brake fluid. Incidentally, I tested the 3+ year old brake fluid in my bike and it was in the 1-2% range.

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 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. From what I have read, moisture and chemical degradation caused by moisture are the potential shelf life issues. So I postulate that without moisture, there is no chemical degradation and thus the fluid is perfectly fine to use. Anyone with some knowledge on this topic care to weigh in?

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?

Mike Murphy

Does brake fluid and water mix together and disperse (diffuse) throughout the entire system?

Or does water stay localized like at the bottom of the gasoline tank, since water and gas don’t mix?

spdracerut

brake fluid absorbs water like a sponge. So technically, you shouldn't use fluid from a previously opened bottle.

polobai

I think using testing strips are the best advice.

Bob Z.

If you only drive on the street there is no need to flush your brakes every 2 years. Think about how many people never change the brake fluid in their daily drivers, or maybe every 5 or 6 years when a dealer tells them they really should do it. I hate to waste ANYTHING but I am not sure I would chance a 12 year old can but maybe you can open it up, test it and see if you can determine it is still good? Not sure how though but Googling might help. But if there is any doubt whatsoever dispose of it properly!

bkrantz

Even opened bottles have a useful shelf life (unless left without the cap on in the shower). A bottle on the shelf is at least as well sealed as the brake fluid reservoir on a car.

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.

JW911

I will definitely test it. A fun little experiment. I suspect it will test at 0%. But we shall see. I am curious...if it tests at 0%, why do you suggest it should not be used?

991.1 Guy

For normal street driving I agree with not changing it unless it tests for moisture. I know DOT 3 absorbs moisture more slowly than DOT 4 which is why most street, non performance vehicles use DOT 3. My truck has had the same DOT 3 in it for 20 years and I bled the brakes recently when I changed the pads and the fluid looked perfect. I have heard that corrosion can be a problem with moisture in the system, so that would be a reason to check and replace, Otherwise I'm not sure you're really gaining anything. At some race tracks they will test your brake fluid for moisture as a safety precaution, so it must be a valid indicator.

koala

I was admonished for using a fluid tester on my Porsche. However, I think measuring the moisture content at the reservoir is a "good enough" indication for a street driven car as to when to potentially change the fluid.

worf928

And then get a $4000 bill because they need a new brake master cylinder, clutch master, slave, and a couple of brake calipers.

Just happened to a non-Porsche friend of mine. No brake fluid flush for 12 years.

Mike Murphy

It’s a good point, given how inexpensive and easy a fluid change is and should cost. I say ‘should’ cost.

I think another point is, though, is there any difference between 2 years and 12 years? Is there a difference to how the car is stored (in a climate controlled garage versus on the city streets)?

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.

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.

991.1 Guy

Let me guess, your bother-in-law's friend's cousin's son? I've never heard of it happening like that but I'm sure there are some dealers that would tell you it did. LOL!

OliverK68

https://www.albadiagnostics.com/shop...20bulletin.pdf

worf928

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.