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Originally Posted by nrgetic99
With all due respect, changing a premium synthetic oil more often is not going to have a major impact on the mechanism for this particular potential mode of failure. However, I am happy to hear a reasonable technical argument that relates to the lubricant that may support this theory. Checking the separator and hoses often is a better option.
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I agree with the above. We don't know that the engines that failed all had premium synthetic oil. I would use a good synthetic, and if I was getting signs of emulsion sludge I would change the oil more frequently to flush it. Without getting into the lubricity questions (my tribology courses were 27 years ago) I would just focus on the visible signs of condensation. I go back to my point that this starts with short trips that don't boil off the condensation. The engine simply needs to get good and hot every now and then. We get posts such as "I only drove to the store" and "I left it idling for 30 minutes with no load in the cold and it got a hydraulic lock" and I think that those driving habits are the biggest contributor.
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In essence, one of the bye products of combustion is water and how it is dealt with is the major issue...if the engine is allowed to warm throughly, the water is driven off or evaporates and will not collect or freeze at local cold spots. Short trips in cold climes do not drive off/evaporate the water.
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Bingo. We have raging agreement!
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As you rightly state, driving habits are the biggest casual factor combined with a design oversight, weakness or fault depending on your perspective.
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I think that is fair, there are multiple perspectives. I do think that it would be better for BMW, and BMW owners, if the original design didn't allow this to ever happen. Having said that, proper maintenance (including the use of quality synthetic oils), not idling for extended periods in cold weather, getting the engine properly warmed up, all greatly reduce the odds. If a vehicle is 4 or 5 years old, cleaning out the crankcase vent lines seems like a very reasonable preventative maintenance step. I think BMW should put that in their Inspection II, rather than moving to heated vent lines. Most owners never have this problem. Some do, and it is unfortunate, but let's keep it in perspective. It is much more likely to not happen than to happen.
We could debate the performance of Group III oils, but I suspect we wouldn't get anywhere, too much of it is anecdotal. Besides, you would leave me in the dust.
Your 20 years is in oil formulation; my 25 years since mechanical engineering school focuses on engines and service issues more than specific lubrication questions. I don't think this is a lubrication problem.
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One final note, the algorithm that BMW use in determining oil change interval uses, along with other factors, includes the number of key on, key off cycles so a consumer that does a lot of short trips where the vehicle gets started and stopped a lot and sits idle SHOULD have the oil change interval light illuminate sooner.
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I haven't seen that effect. I believe that the algorithm simply counts the litres of fuel consumed, and doesn't consider short trips vs highway. The different km/miles to an oil change is because of the relative fuel efficiency in those two extremes of highway vs city, not because the engine knows how it is being driven. You can see the measure of litres to the next oil change on the hidden menus in the OBC. There is no count of starts/stops to my knowledge.
Good discussion, as engineers are wont to have. One last question: Do you have any indication that the original stumbling was caused by this problem?
Jeff