Quote:
Originally Posted by ants_oz
While not disputing some of the claims made here, I do find it interesting (some might say amusing) that other complex hydraulic mechanisms (in such things as excavators, hydrostatic drive units) have no such claims to "lifetime fluid". Our excavators - we would NEVER dream of running the hydraulic drive oil for more than a few hundred hours at most. Our large mowers - same thing. The hydraulic fluid is lifeblood to these machines, and we're not talking a few grand worth of transmission - we're talking tens of thousands of dollars worth of repairs if you have a hydraulic issue that contaminates the system.
I suppose though, since the X5 really is aimed at the general consumer market, they (BMW) can make the assumption that for the vast majority of purchasers there will never be an issue in the "lifetime" (ie economical repair life) of the vehicle, so the claim can be argued as valid.
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My career background was in heavy equipment service (yellow machines from Peoria). I think there is a fair bit of difference between an automotive transmission and a hydraulic circuit on a tracked excavator, for example. We used to look for metal particles by connecting up particle counters on the return lines, and extending/retracting boom and stick cylinders, till we found the spike. The metal came from the cylinders fairly often. Not a failure mode that transmissions see. We don't see metal particles, we see burnt fluid from overheating, when that does happen.
It is an economic, life cycle cost calculation, at the end of the day. And that refers to the transmission life. I believe that the transmission will more likely fail from some other cause, whether electronic sensor or wiring harness or whatever, before it fails due to fluid degradation. Not always, but frequently enough that replacing fluid is a questionable economic investment. If the fluid was overheated due to some other problem, sure. But now that we have lock up torque converters, and ECMs that back off the power during shifts, and have sufficient transmission cooling to tow 7700 lbs on 12% grades without additional coolers, the transmission is pretty much set. BMW is even warming the trans fluid on a cold start to reduce wear. None of these things existed in the days of 3 speed slush boxes that burnt their fluid every 30,000 miles.
There is lots of discussion on the risks of failure post-fluid-change. I contend that it is a real risk, albeit a relatively small one. It is just that I don't see the upside, the statistics on how replacing fluid has extended transmission life. No data whatsoever. But we do get reports of failures, apart from those where the wrong fluid or filter was used, or where there was already a problem. In the past decade, maintenance planning has moved into the science category, while some are still doing things and spending money just because they feel good. I'm all for feeling good, and if it feels good do it, but don't pretend that it is going to extend the transmission life unless there is some rationale other than "that's the way we always did it".
Fun topic. Even with sunny, who is still singing about old wives and urban myths. Same as last time around.
