I believe all modern cars have an oil filter bypass in case the filter gets clogged. All of mine (prior to the BMWs) have had one, even my 1955 MG TF1500. Very early VWs didn't have one, though. So I assume BMW has the same thing.
And, I am sorry if I sounded like the heavy oil was your only problem, just that I thought it was TOO thick for your current environment ...
I totally agree with you here jclyman. It probably does have a bypass but I still think the oil is way too thick for the temperature outside. The block heater should do the trick and also switching to a thinner witer oil will solve my problem.
Cheers.