Hi,
Dennis - My Boxster was on M1 0W-40 from new. When I purchased it I "modified" it to run a little warmer than stock and felt that I needed a slightly higher HTHS vis. This is probably overkill as the coolant/oil interface never goes beyond 105C anyway
I live in the Tropics (a cold winter's start is around 15C, a cold summer start is around 24C - a normal winter's day is around 24C and a summer's day to around >40C) and I do a lot of long distance trips
I've run Delvac 1 5W-40 in every "modern" Porsche I've owned - and HDEOs in most of my engines since the 1960s. My last stock of Delvac 1 5W-40 is almost gone too!!!
The Boxster will be getting M1 0W-40 at its next OC - my Benz will stay on it. It is a true "Premium" lubricant with a very very long and successful history!
I don't believe a SAE50 lubricant - even M1 5W-50 which is also an excellent lubricant - is warranted in these engines in typical use!
I also believe that a Non Approved lubricant (except for some HDEOs like I use) can be counterproductive in some Porsche engines - this has to do with viscosity retention and foaming
Many Porsche engines have more than one oil pump, a "dry" sump of some configuration or other (as in the M96) and quite complex valve actuation - typically with buckets - so superior flow characteristics are warranted at all temperatures
I hope this explains the reasons
