I never said formal proof was bad. I said it wasn't required, and sometimes isn't possible. And actually a lot of engineering is on "faith". Faith that we understand statistics and can correlate things from non-direct data sources. Correlation is a very "fuzzy" science. We are trusting that things "work as they should". Usually by some spot tests. Accelerated vehicle durability is a route that a car is driven over and over again (sometimes by a robot on the proving ground) that route has some basis in data and reality, but even then it might be "lost to time". However if we pass that test, we feel comfortable that the car has been "through the paces". This is how all DV/PV is done, there are tests. Are we testing everything? No. During production do they test every part? No, they will pull so many a day and run some tests on them, and we have some checks for basic stuff like torques or cameras to take pictures of processes which are known to be troublesome. But that part is still "certified" to be identical to the ones which went through the full DV/PV. You're approaching this from a VERY RIGID test based results driven way.

Not debating the "correct" thing to do. Debating weather its actually needed or if its more of a cover your *** type thing. I don't know if the 3% is the line. I'd say take one of those kits, jam it into the brake cylinder of a 12 year old car that's never had its fluid changed and whatever number that comes out I'd say is acceptable. If you want more than one sample, take 25 random older cars. If the result of that random sample was 10%, then I'd say 10% is fine. I'm a practical guy and if the mean percentage of moisture people are driving around with is 10% then its likely fine.

Germans also FYI are the most **** retentive when it comes to doing the "correct" thing, to a fault. I see this with my family and my colleagues in Europe. That's not a dig at them either, its just they are overly conservative and always want to be absolutely "correct". Japan works slightly differently in that they look for the most efficient/optimized way even if they sacrifice being absolutely "correct", and if anyone is the "most casual" its the US. I assume this has to do not only with cultural things, but also who actually is in charge. In Germany and Japan the engineers have more say, and the business people less (although this is changing in the last 10 years as we poison the world with our business consultants). The US has always been very business driven. To be honest, the best way to get your way in the US is to leverage a cost, legal liability, warranty spend, etc to argue a point. To say "this is the most correct way to do it but costs 2 times as much as this other way" will usually net the response, well "what's the negative of doing it the other way?"

If I were to tell you why it says 3 years in the service manual in the domestic OEMs it would be because that is a "industry standard" and can be argued against in liability cases if you don't follow it. Or at least I would say that is the thinking and reasoning of putting in the owners manual like that. In fact a lot of service recommendations are for that reason. Just as the technician says he'd change it at 3 years regardless due to liability, its in the book for liability.

Europeans, also FYI take their cars on the regular to the dealer for service and follow the service schedule to a T, sometimes because its required by law (you won't get TÜV approval without certian maintenance done). My uncle for example goes twice a year to get his tires swapped, and at one of those they do the yearly service. This is why the European manufacturers also have the most "stringent" maintenance service, cause it WILL be done. At least in Germany.

 

Warranty is a whole different animal. Probably won't become an issue but why chance it?

Cost me $40 to know that I can extend it to 6000 miles on 0W40 Supercar with the way I drive. OLM hacked off 33.33% of it's life and I could have gone 6000 instead of 4500. On the older 5W30, IDK. If I can leave it till spring and test it, I would be able to have a peek at whether the OLM hacking off 8.33% every month was too conservative or not. My car was built around 5W30 Mobil so, if anything, it would be too conservative. Costs me less than $50 to know for sure. For that, I can save that much and 2 hours of wasted time PER unnecessary oil change. If the OLM was right, I lose the testing money. Cost of doing business. When I test the 5W30 oil, I can, WITH SOME DATA, decide if the extra cost of the Supercar oil is worth it. Again, why guess when testing isn't that difficult or expensive?

 

As an aside, I'm doing a highly unscientific survey of my engineering, mechanic, and car guy friends (about 20 people) asking them how often they think people change their brake fluid (and other fluids) and so far the consensus of the group is the following:

1. "No one" follows (one guy attempted to quantify that by saying 70% don't) the maintenance schedule on a lease (unless they have free maintenance) or older car with the exception of semi-regular oil changes.
2. If a median time were to be guessed as to how long it was before people changed brake fluid the number was 5+ (some said can't have a median as too many never change it)
3. This does not apply to anyone who tracks their car or does any sort of performance driving.
4. Most fluids are only changed when a part fails that necessitates the fluid to be changed. So in this instance, no leaks, no caliper seizing or replacement, no new fluid.

I brought up the testing kits in this thread, and the majority of people where amused by them and said "no one" would buy those and test their fluid. I'm still actively getting feedback so some of this might even get more hilarious. I got a lot of laughter when I summarized the expectations here of people changing the fluid every 3 years.

As a double aside most of them told me they themselves don't change the fluid. Some said they have never changed it on any car they've owned. One guy who I'd consider the most diligent, said he does 5 years on his cars.

 

I don't disagree it is sometimes cost prohibitive or really impossible and we have to take a stab at it with the Ouija Board with the worst case scenario but therein is the question. If it isn't cost prohibitive, why not test? You seem to be of the "Test as a last resort" mindset.

THAT'S my point. If you had 20 scientific papers that said 10% is fine, I'd run with that. I haven't seen anything else that says that significant degradation of performance won't occur until 10% so say 8% is fine. If 3% is the magic number, I am already at high 1s to low 2s by 2 years.

In the US, as I understand it, they calculate how much it will end up costing them and decide which way is financially best. If the recall costs 10 million but the cost of not doing it is 3 million including the lawsuits from a couple of dead people, so be it. As to culture, I got no clue. I am much closer to the Japanese culture by birth with nothing in common with Germans besides being bipedal humanoids but I much closer to the German way as you describe them. I can't even think of any true German friends personally.

No argument. Domestic manuals are definitely financially driven. Is that good or bad? Depends. As a shareholder, it is great. If not, perhaps not.

Again, don't know. Perhaps they don't have so much of a "Hot Rod" culture where you and Dad spent the weekend playing with the car and thus not so specific. Perhaps after WW2, they had to stretch things out instead of being so "disposable" with stuff and good maintenance is seen as a very good way to make it last.

 

As a triple aside, I'm asking my other friends who aren't engineers, mechanics, or car guys, how often they themselves change their fluids.

Results so far are ranging from "I need to change that" to "uhh, never."

Obviously not a very scientific survey as the sample is not highly randomized. But honestly if this group isn't doing it, I'm going to guess most people aren't.

 

2 years. Every odd year per MB standard. I have one of THESE with an adapter for a Ford to make it easier and I do it for the UTV and Trike. The UTV (for obvious reasons) hits the 3% mark by 2 years and some change. Yes, I also own THAT. Maybe you should also ask how many of them own a newer German car where they definitely suggest it every 2 years if you take it in for service.

 

My parents own BMWs.

2004 5 series, we did one brake fluid swap around year 10 maybe it was 15. It was like, OK this has been in there long enough. No other fluid swaps. Was bought 1 year old. Sold during the pandemic it was 18 years old I think.
2014 X3, never swapped any fluids. Was bought 4 years old. Just sold earlier this year
2022 X3, no plans to swap the fluids. Was bought 3 years old.

Semi-regular oil changes around. My dad does 2 years unless they put on some miles (they usually don't). He's a retired mechanical engineer. Has always wrenched on his own cars. Can't say if the dealers did any work when it came off lease, based on the CarFax I'd say other than some oil changes (and we don't think yearly) on each we can't say.

 

Update to this. I have an outlier! One of my friends in Florida actually DOES change the brake fluid on his cars every 2-3 years. So far he's the only one.

Of the other people who did it was over 5 years or they gave me a mileage (which I used to estimate over 5 years). But most were never changed a fluid outside of the oil.

 

Since I have owned MBs, back in the 90s, they have had brake fluid changes scheduled for 2 year intervals. When did GM or any domestic manufacturer start recommending flushes? I am thinking maybe the last 10 or so years?

 

I just pulled up some 2016 owners manuals from Ford. They have nothing about changing Brake Fluid in them. My 2016 Corvette does obviously. I pulled the 2004 Malibu owners manual (used to own one) and it says nothing about Brake Fluid changes.

 

Decided to look up the 2014 X3. It says no surprise 2 years for brakes. But surprisingly, also 2 years for oil. Well well...

"Determining the maintenance intervals according
to the actual loads on the vehicle covers
practically every kind of operating situation.
However, even those who drive only short distances,
significantly less than 6,200 miles/
10,000 km annually, should have the engine oil
changed at least every 2 years since oil deteriorates
over time, regardless of use.
Brake fluid is hygroscopic: it absorbs
moisture from the atmosphere over the
course of time. To ensure that the brake system
continues to provide safe and reliable performance,
remember to have the brake fluid
changed at least every two years by a
BMW Sports Activity Vehicle Center, also refer
to the Service and Warranty Information Booklet
for US models or the Warranty and Service
Guide Booklet for Canadian models."