Quote:
Originally Posted by jpcoop
Agree. Lots of armchair quarterbacking from non-experts on this stuff. Makes no sense to me; seems unlikely that any of the people debating around in the forums know more than the engineers that designed the thing.
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not always, sometimes the engineers get it wrong:
The BMW M3/M5 models have had an ongoing problem with rod bearing failures for a number of years now. The M3’s S65 V-8 engine was derived from the M5’s S85 V-10 engine. They share the same basic architecture and aluminum construction. After going through all that, it turned out that the root cause of all those failures was that BMW had designed/built the engines with insufficient rod bearing clearance (barely large enough for 5W30 motor oil and WAY too tight for super thick oil), insufficient connecting rod side clearance, and they called for insanely thick 10W60 motor oil, which is WAY too thick for acceptable oil flow/lubrication/cooling. It was a perfect storm of doing multiple things completely wrong to actually “cause” rod bearing failures.
It was noted that along the way since all this began, that BMW has increased the rod bearing clearance a little, and now also allows the use of thinner oil (though many owners still seem to think they should use super thick oil for protection). But, there was no mention of them increasing the rod side clearance, which needs to be correct in order for oil to properly flow through and out of the rod bearings to provide the critical lubrication and cooling they need to survive.
Note: the above was taken from the 540 Rat oil blog.