Quote:
Originally Posted by Penguin
When it cones to wear and things oil impacts, I see a lot. Has BMW gone away from plain bearings? Are tolerances and clearances bigger or smaller in newer engines? Are newer engines more or less susceptible to oil viscosity changes?
Newer engines are more demanding of oil than older engines. The justification for longer oil change intervals has much more to do with engine oil changes than with engine design changes.
While I must admit I am not an "engine man," I also have a Mechanical Engineering degree and a bit of a mechanic background.
So you may be quite correct, but since I do my own oil changes, I personally prefer to err of the conservative side and not go for the extended oil change intervals. As a former Product Planner for Ford, I do remember being in a couple of meetings between marketing and the engineering people arguing about service intervals, with the Marketing people pushing hard to extend the intervals, to get a sales advantage, and the engineers arguing against extending them. It was more like an adversarial negotiation than discussion of facts.
I imagine even BMW internally has similar "meetings."
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Metalurgy has changed over the past few decades. Tolerances are generally tighter, and surface finishes better, meaning that the engine is smoother-running and has fewer corners to be knocked off (resulting in less of a requirement for an early first oil change). Tighter tolerances doesn't imply to me that the oil passages are smaller, rather that there is less wear metal to clog them.
I am not sure if engines are more or less susceptible to viscosity changes, I would be guessing. But I do know that modern oils (eg API SL, SM) are much less susceptible to changing viscosity. I would say that oils have improved many times more than the demands on them have over the past few decades.
I think that the biggest difference is that we are now running many LEV and ULEV engines. Decades ago, oils were largely degraded by byproducts of combustion in years past. Take away that built-in contamination source, and oils stay clean much longer. We are talking orders of magnitude in the scale of the reduction in contaminants.
I am absolutely sure that there are debates at the manufacturers on service intervals. My dad worked at Ford, I work with another large engine manufacturer. What would be very telling to me is if I saw a modern engine fail from following the manufacturer's service intervals. I haven't. They have safety factors built in. If you are in an extreme service application, you should definitely change oil more often. However, for the vast majority of owners, with normal duty cycles, the manufacturer's recommendation is pretty sound. Changing oil every 3000-5000 miles because we all used to do that in the '70s is, to me, like watching a Betamax on a 26" CRT, defending the picture quality, and claiming that Blu-Ray is a plot by the manufacturers to sell DVDs and LCDs which are no better than VHS tapes. Technology has moved on, on many fronts.
I am not out to change anyone's oil change habits. We will all do what we want to do. I change oil myself (as you do) because I like the experience, it is honest work, it feels good. I just don't think that new owners should be led to believe that they have to change oil more frequently because of a supposed plot by the manufacturers. There is no connection with free maintenance and extended service intervals in BMW's case (very few countries get pre-paid maintenance, while all got the extended service intervals).
I agree with others that there isn't a resolution to this eternal debate (until we see a deluge of failed engines from following the manufacturer's recommendations) but at least it is entertaining.