Buster,
For oil of a given SAE grade, there is a very strong correlation between Noack volatility and oil consumption in actual service. If you have an engine in good condition, most of the oil consumption is simply from oil that evaporates. These oil vapors are then recycled through the PCV system and burned in the engine. That is why the API and ACEA continually strive to impose more stringent Noack limits every time a new oil spec comes out. One of the main reasons for the 1000 ppm Phosphorus limit on API licensed oils was due to the high evaporation rate of 5w-30 petroleum based oils that are the current standard for most gas engines. The thought was that burning this much P was not good for oxygen sensors or catalysts ....
If you are talking about oil consumption in very high mileage engines, different mechanisms may be taking place. In these cases oil may be leaking past the valve stem seals or oil control rings directly into the combustion chamber. Going to a significantly heavier oil is about the only way to reduce oil consumption under these conditions.
Watch what happens to oil consumption when "3MP" starts running the Amsoil 5w-30 in the LS-1 engine. I predict a reduction in oil consumption of 30% to 50%, mainly due to the much lower evaporation rate (4.9% vs 9.2%) of the Amsoil 5w-30 vs the M1, 5w-30.
You can always find a few exceptions to any rule, but I think the data in this case is very convincing.
TooSlick
[ June 05, 2003, 03:00 AM: Message edited by: TooSlick ]