Hello All;
Thanks for all your comments.
I suppose my situation is one of the often discussed examples of "my car burns Brand X", but not Brand Y".
In summary, both my BMWs quickly lost 2/3 to 3/4 quart of the Liqui Moly Leiachtlauf HT 5w-40 (both have the same 6.9 quart sump capacity). Using my wife's 328i as the example, this was a 10.9% loss of oil volume in just 128 miles. 100C viscosity increased 9.1% in that same 128 miles (see the VOA and UOA at the beginning of the thread).
It is my belief that the oil consumption using LM was not piston ring blow by, but was rapid oil evaporation caused with the initial heating(s) of the oil. The oil vapors were then drawn into the PCV system and fed into the intake.
Castrol, on the other hand, does not exhibit this behavior. Using Castrol, my 330Ci consumes no oil at all for the entire OCI. After switching out the 328i from LM to Castrol this past weekend, I had to top it off with no more than 1/8 quart after the first 100 miles. This is radically different behavior than I saw with LM, behavior I have more confidence in (confidence in Castrol).
If our BMWs were DI engines (they're not), and I saw both consume 2/3 to 3/4 quart of oil over an OCI using LM, but only 0 to 1/8 quart on Castrol for the same length OCI, I would not recommend LM because of the potential for intake valve deposits. There may also be a risk to the cats as well because the oil is making its way out of the engine via the exhaust.
It seems that, even with the Liqui Moly Leichtlauf HT 5W-40 having all the same approvals as Castrol Edge 0W-40 (in particular BMW LL-01), neither of our BMWs seem to like the Liqui Moly.
And this is the issue I cannot seem to grasp - why two oils with all the same approvals (and viscosity), exhibit such different behavior. I would have expected virtually identical behavior by both of these oil choices.
This tells me that there are real differences in oil brands, even if they have the same approvals. I often see people suggest that it makes no difference which oil is used so long as it has the proper approvals - they're all just as good as each other. In my situation, with both our cars, this is obviously not the case. There is a difference, a big difference.
Once again, thanks to all of you for your time.
Scott