I am the one that has serviced the car for the most part while it has been in the family since 1984. It is an '81 380SL. And yes, the fluid does absorb water as easily as alcohol has such affinity. I posted my experience for those that like to learn from others' experiences and to learn about the nature of automotive systems. If you don't care to listen, I certainly don't care if you don't.

BTW, I have done quite a bit of work on the car in my own garage. I removed the engine and transmission years ago and installed the double row cam chain to bring it up to date. That was probably 10 - 12 years ago. Not my first rodeo with autos.

 

I won't argue with that statement. Propylene glycol is extremely hygroscopic. I just think there's a little too much "fake news" here that's being propagated by some that's probably not worth being considered as gospel by all.

All this is essentially irrelevant as you're not the OP (original poster). I'd like to commend you on your ability to do your own wrenching, but you otherwise present nothing useful to the subject. In fact you're boasting working on a vehicle from a different manufacturer and from a completely different era. I understand that my attitude is abrasive, but what exactly is your point (rhetorical question). The fact that you own a sports car doesn't somehow make the laws of physics different.

As I alluded to previously, I've owned two GM vehicles and one VAG (Volkswagen / Audi) that I've purchased new or second owner that had original brake fluid that survived > 10 years or 245k miles and never had a hydraulic issue. In fact, the Volkswagen still had the original brake fluid in it at 506k miles when the booster seal failed and subsequently destroyed the master cylinder seal.

If you want to change your brake fluid regularly I'm not discouraging that, only pointing out that it's utterly and completely unnecessary.

FWIW

 

For the sake of others on this forum that are unfamiliar with the subject I would suggest your statement maybe should not be taken for an educated assessment. just sayin'.

 

Many track day organizers require fluid to be less than 6 months old. I've boiled 6 months old fluid on track and haven't boiled fresh fluid.
If you're planning to take your car on a racetrack , please flush your brakes. Your mileage probably won't vary.

 

I'm not following your logic here Grinder. You don't change the fuel filter because it's filtering better than new and not restricting flow? How is that different than oil, transmission, and air?

 

I agree with this statement completely. Road racing puts an entirely different level of stress on just about every component of the vehicle. I would also recommend a premium DOT4 such as Pentosin or something with a dry boiling point > 500f. But the OP didn't mention racing. If you primarily use your car to "get groceries" and only occasionally need some heavy braking entering a curve on a windy two-lane, I stand by my initial statement(s). There aren't many public thoroughfares that will cause one to boil even the wettest old brake fluid unless they're driving at ridiculously irresponsible speeds. I will openly admit I drive like an asshat more than I should, but even the autobahn has traffic.

Curious, is there some kind of test for this requirement? If so, that would be a fantastic indicator (i.e. a measure of absorbed moisture content) for when to change your fluid.

 

Here is only one of many types to test for moisture in brake system.

Phoenix Systems BrakeStrip Brake Fluid Test Strips 3001-B

 

With an oil filter, if it is plugged badly enough, the bypass feeds unfiltered oil to the engine. Better than no oil, but terrible compared to a new, proper oil filter. Most of us change oil regularly, say every 2,000-5,000 miles. I think it's foolish to start out with the filter holding 1/2-3/4 quart of dirty oil. So I always change it, and thats probably why the rest of us do, also. The fuel filter has no bypass. It either flows enough fuel, or it doesn't. But it's clean fuel. Since I have no issues with fuel delivery, and no clogged injector issues, the filter is doing its job, as good as, or better than, a new one. The trans filters are better than the old, plain screen type, but if it clogs sufficiently, trans clutches will suffer from not enough pressure. The trans filter lives in a high heat, constantly deteriorating fluid environment. On the air filter, power will suffer, and so will fuel mileage. With the trans, oil, and air filters, they are all always in a contaminated environment. As the trans and oil filter age, the ATF and engine oil deteriorate from the moment you start the engine. Same with the air filter, with some areas having much cleaner air than others. But all areas have dust and dirt particles that slowly clog the filter to a degree. Fuel is pumped from modern pumps that usually incorporate pump filters. So fuel entering the tank is (theoretically!) always clean. With around 132,000 miles on my 2000 fuel filter, it either passes enough clean fuel, or it doesn't. A 427 will quickly put a partially clogged filter front and center. My engine runs as good as I could possibly expect. Also, the fuel must be clean, as the engine has never had injector problems. If the filter was damaging the engine or trans, I'd change it. Often. But the other filters you mentioned can cause serious damage if they are dirty. A dirty fuel filter won't damage anything. When it starts clogging, it will show with the engine not receiving an adequate fuel supply. Most of us know what an engine running out of fuel, or not getting enough fuel, sounds/behaves like, and then we can change the filter with no harm done. I hope this explains why I've never changed an EFI fuel filter, in over 1 million miles of driving EFI cars.......

 

"Curious, is there some kind of test for this requirement? If so, that would be a fantastic indicator (i.e. a measure of absorbed moisture content) for when to change your fluid."

Yes there are a number of brake fluid moisture analyzers available, here is one:

Whether any of them are reliable or accurate, you have to read the reviews.

 

28 replies, and so far, nobody has been able to answer my original question........

 

Welcome to the interweb! To answer your question, I extract the fluid that I can from the reservoir and then fill with fresh fluid before flushing. I run a liter of fresh fluid through a couple of times a season so figure even a little residual fluid will dilute.

 

I think the lack of answer tells me you are too worried over an ounce of dirty fluid.

 

I like to be thorough..........

 

$75.00 for 100 strips......Summit must think you'll test your brake fluid 10 times/year for the next 10 years!! I could see 5 guys going in on this for $15/20 strips each. But 100 strips is one Helluva lot of strips!!! Thank you for posting a source, though, and HAPPY NEW YEAR ALL...

 

Just push more fluid through until you're confident the old stuff you couldn't suck out has been pushed through the bleeders. I have a syringe with a vacuum line hooked up and even that won't get in that front section to suck it dry. Take solace in the fact that the front of the reservoir is for the rear brakes.

As for those that seem to love old brake fluid, well, more power to you. You're probably the same as the ones who never ever flush power steering, diffs, transmissions, or anything else other than oil. Just because it keeps working with that old garbage fluid doesn't mean it's the right thing to do, and judging it by the fact that, by dumb luck, you haven't experienced a failure again isn't proof that it's the right thing to do. If you truly believe that, I challenge you to start neglecting engine oil changes and let me know how that works out.

 

Your Master cylinder shouldn't have dirty Oil in i EVER! it should be clear Maybe a Little Golden BUT defiantly not dark or Black If it is you should replace the master cylinder.
You can buy a New Master with a new reservoir fairly cheap. OR if your smart enough Master cylinders are fairly easy to rebuild then clean your reservoir before Bench bleeding.

I never drain mine if they are dark I replace it, With new or rebuilt unit after bench bleeding install it. Then continue to bleed all Calipers in order till each runs clear fluid out of it.

 

Understand your point, but in today's cars, with ABS systems, replacing the m/c is the EASY part of the job. PROPERLY AND COMPLETELY bleeding the system, can be the tricky part....

 

Engine oil changes are a totally different thing. Please see my post above. BTW, I have changed my own trans fluid (ATF). I have changed my own diff fluid (gear lube). I've changed, and built my own engines. Fuel is changed more often than I'd like , and always replaced with clean fuel, which doesn't deteriorate unless car is stored. So not all of us ignore everything, though some probably do. Brake fluid (nope). Original master cylinder, too. Car stops just fine, and I take car out in the rain, maybe once a month, to "exercise" the ABS. 23 year old ABS unit, still works as new. So, not all is wrong in the braking department. Still stops hard from 130+mph down to 30mph. When you're doing 130-135mph, and have 1,000 ft until the pavement ends, it damn well better. If some people want to change brake fluid 1, 2, or 3 times each year, go for it....

EDIT: Forgot about the power steering. In the 3 cars, and nearly 1 million miles I posted about earlier, I've never bled/changed that, either. I have added fluid to the C5s power steering reservoir when I've changed cams, and lost some due to the rack being removed. But car still steers fine, and easy, with no leaks or hydraulic "moaning." So did the other 2, 400,000 mile Buick, 360,000 Jeep GC.

 

The more you explain your reasoning the more logical inconsistencies come up.
Based on your posts filters get more efficient as they collect impurities and you never change fuel filters. But air & transmission filters get changed even though they get more efficient as they become clogged. And unfiltered things like rear end, brakes, and power steering don't get changed because... reasons.
As someone reading your posts I'm not able to apply your advice to other situations since they don't seem to make sense.

 

I forget. What was the question?