Quote:
Originally Posted by ard
So lets take this conversation to the extreme-
Lets say, for the sake of argument, that we agree that the conditions that are outlined in the ZF document are never achieved in our use. So never high temps, never towing, etc, etc....
The logical conclusion per the document is that the fluid will last FOREVER... how is this possible? It is flat out nonsense. I dont care if it it 100k miles, or 10 years, or 20 years or 50 years.... it is NOT POSSIBLE for oil to last forever. And for BMW and ZF to 'pretend' this is true is disingenuous.
Now, that brings us to the 'space' betwee 'forever' and '8 years or 80k KM'... I believe that degradation and damage to molecules is cumulative, and os not a binary event- it is illogical to imagine that as long as you do not hit those stated conditions that fluid will therefore remain unchanged....
One thing we can agree on is this: vanishingly few of those reading these posts today will own the car when issues with ATF come home to roost. (They will fail for other reasons, or owners will just move on.)
Finally, I am 100% convinced that the "system manufacturer" does NOT have OUR best interests at heart, and is not driven by the primary design control input of 'longest transmission life'. (IMO, they are driven by 'lowest overall ownership cost to first retail purchaser', 'lowest maintenance cost to BMW', 'lowest repair rates to BMW'...etc.)
Say, haven't we been here before? 
A |
Disagree that they are saying forever, they are saying the service life of the transmission. If the E70 isn't going to last forever, why would the transmission need to?
Let's analyze the statement "oil can't last forever". Why not? Oil never stops being slippery, in the life spans under discussion. It gets contaminated, the additives lose their effectiveness, and I would agree with you that the viscosity can change. However, viscosity change is probably the last one I would worry about. It just isn't a very demanding lubrication requirement. The viscosity spec is quite wide. And, the transmission adapts to viscosity changes by monitoring shift times, etc. The oil doesn't have to remain unchanged, it just has to remain within the service spec for the service life duration. If they can't design sensors and wiring harnesses installed within the transmission to last 20 years, why would they need to design a fluid to do so? There was surprise expressed above about it not even being a fully synthetic fluid. My point is that given the low demands on it, it doesn't need to be fully synthetic. (It does cost like it, though. Funny how that works).
BMW and ZF care so little about replacing the fluid that the service instructions tell the dealers to drain the fluid, and put the same fluid back in, when repairing the valve body or minor components in the transmission. That takes time and $$ for the dealer, it is a hassle. But BMW would rather the transmission not have to adapt to new fluid. It isn't done to save money on fluid.
And as with previous debates, we both agree that while this is all technically interesting, it comes down to a discussion of how much it matters. There are other places on the vehicle that I would over-maintain, instead of the transmission, for the same investment.
I agree with some of your comments about what is important to BMW. To your points about lowest cost to various stakeholders, which I agree with, I would add protection of the brand name. That is more important to them than service costs, in my opinion. It is why they called and just gave me a new high pressure fuel pump on my 535i, even though the one they installed two years ago (when the original failed) was working great. It would have been cheaper for them to wait for it to fail, but less convenient for me. I don't think that longest transmission life is on their list of criteria, and properly so. I suspect it is 'sufficient' average transmission life. I have worked on Rolls Royce vehicles, years back, and they had many components designed for 'longest possible life'. It cost a lot, in design and manufacturing, and service. I don't think most consumers want to pay that up front when they purchase a vehicle these days.
Yeah, I remember being here before