BTZ461 said:
However the items you refer to have both drain and fill plugs
Diffs on the standard Z4s lost the drain plug around 2007 IIRC (I have a 2006 that still has one and went to check before I bought oil.)
Lifetime oil is an interesting thing. I hadn't realised that BMW had gone to a free maintenance model which does explain the outbreak of them. However, realisitically, diffs and manual gearboxes aren't particularly hard on oil in passenger cars. To a fair degree they'd run for a long time if they were just filled with jam so the idea of an oil that's left alone for 20 years isn't particularly hard to swallow. At the end of the day it's just a bunch of gears sat in a bowl of oil.
I changed the diff and gearbox oils in my 2.5 recently at 95k and 16 years. There was nothing particularly nasty about the old stuff and new oil might have made the gearchange a bit sweeter but it's pretty marginal and, crucially, Jo Soap owner number 4/5/6 wouldn't neither know nor care. Once cars become cheap maintenance goes out the window and, bar the small bucket of enthusiasts, few would bother even if mechanics suggested it.
I have been lambasted left and right on here about the high mileages of my other cars (
) and the one thing that's going to kill my 275k 320d isn't old diff oil (although I did change it at 160k) but rust (going a bit crispy), sudden failure of turbo (original) or finally wearing thru the clutch (also original) on a car that's worth less than the contents of its fuel tank (poor thing.)
Autoboxes are almost little different but they are harder on their oils. I changed the X5 oil at 150k'ish (and, to reiterate, 15 years old, long after the point at which it's just a few grand of 2nd hand car) and it wasn't horrendous. Presumably the additives were still working and nothing had chemically broken down as it wasn't a stew of burnt clutch plates. However, the one important thing is that there is a filter that does collect these bits of material and not changing that is A Bad Idea. Fresh oil in an auto can only be a good thing too so that is something that ought to go back on the schedule.
One final point, in industry changing oil is done by time because of static engines, etc, and, by comparison, cars run for nowhere near as long, maybe 500 hours a year. Cranes and other things doing a damn sight harder job probably have a gearbox schedule of 2500 hours. That'd be 5 years for a car but, as said, it's just not stressed enough so, realistically, it would be many times this. Long after the rest of it is iron oxide again....
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