I found this post from one of the oil gurus at Clubb5.com which is the VW Passat site. The Passat's generally have the VW/Audi turbo 1.8 engines so this person maybe speaking to the 1.8 engine. Regardless, I thought I'd get some of your thoughts on this:
-------------------------------------------------------------------------------- I am going to get very technical here. Reynolds' equation is used to relate the thickness of the oil film required to support a load to the minimum viscosity required to maintain the film. From Reynolds, one can propose a film thickness and calculate the minimum viscosity. This must take into account the average surface roughness of the materials as the film height must include the maximum dimensional tolerances. This will give the minimum viscosity required to maintain a hydrodynamic lubricant film. To reduce the minimum film thickness required to support a load, the other two regimes of lubrication must be called into play. These are boundary and Extreme Pressure. Both are dependent on an active oxide layer on the metal surface. If the oxide is abraded or worn off, these lubricants ("additives") will not be very effective. The role of an anti-wear agent (the beloved ZDDP) is to replace the oxide film with a more tenacious and reactive layer and render the boundary and EP additives functional in a high wear situation. What the Dr. is describing is what happens when the viscosity of the oil is too thin to support the film thickness required to maintain a hydrodynamic film and the additives are insufficient to prevent catastrophic wear. No motor oil has sufficient additisation to prevent catastrophic wear under sub-par film conditions. In the high-speed environment of an engine, there is little reason to run at the ragged edge of viscosity. You are playing with your car here. TBH, newer synthetic stocks are available which have massive VIs and can meet the 0W40 specs with very little VI improver. If you are complaining about the price of Mobil1, don't even ask how much these oils cost. Since 0W oils inherently lack film strength at certain temperatures due to reduced viscosty, I strongly recommend against them for normal use. The drive to 0W oils comes from fuel economy standards. As the engines becomes trobologically optimised, the principal contributor to reducible friction is the internal friction (viscosity) of the oil. Since this can be reduced, that is what is going on with the demands by the engine builder for 0W. Supposedly the reduction in internal friction makes a measureable contribution to fuel economy. With the demands of the CAFE standards, any little bit helps.