Maybe it would help to clarify something I said earlier...
On certain industry standard engine tests, you can show that oil loss is crudely proportional to Noack. Now these tests are run on brand new engines with the engine running flat out and with the oil kept at an artificially high temperature. Unsurprisingly most of the oil loss is via the PCV/intake system and should be considered as evaporative loss. These engines, which might run for just over four days continuous before being junked, do not suffer from problems with worn valve seals or old leaky gaskets. Also, even when a relative large amount of oil is routed back to the cylinders to be burnt, it is rare that you will stick an oil control ring. As with most sticking situations, you need quiet time for the glue to set solid. You just don't get that on a four day continuous thrash test.
In reality engines run at far lower oil temperatures so evaporative loss is a much slower process but it should still be crudely proportional to Noack.
However, older engines can develop problems with worn valve stem seals and oil can get sucked directly into cylinders and burnt. This type of oil loss will NOT be proportional to Noack.
If you have a lot of cumulative evaporative oil loss or valve seal oil loss, the sticky deposits you get from attempting to burn oil can work their way down the sides of the cylinder. The compression ring and scraper ring are both, to a degree, self-cleaning as they both splay, invert and rotate. Unfortunately, the oil control ring is not self-cleaning. Excessive oil loss can lead to a stuck oil ring and when this happens, oil consumption tends to skyrocket. Once it starts, this form of oil loss is again NOT proportional to Noack.
My advice is always look for a low Noack oil, or in the absence of a Noack result, choose an oil grade that is likely to have a low Noack. This will minimise evaporative oil loss, which is important but the bigger and far more important reason is that it minimises the risk of developing a stuck oil control ring late in the life of the engine.
Hope this helps...
