stubblejumper wrote:
Oil does not go bad it has been underground for millions of years! additives deteriorate and contaminants get into it. Oil can and has been recycled for years by being filtered and having new additives added.
If the rings on your pistons are not loose or worn allowing blow back, you should not get "soot" in your oil. Most contaminant in oil results from heat burning additives and residuals from engine wear and dust. At Husky we used to sell recycled oil at a lower price. Oil and antifreeze are recycled in Alberta, picked up regularly from service centers by recyclers.
Tests done in 2004 showed new engines have shown 6 to 7% soot content in the oil in 12K miles as a result of EGR.