Join Date: Dec 2007
Location: Chicago, USA
Car Year: 2005
Car Model: Forester X
Feedback Score: 1 reviews
Yeah, all engines use some oil. It gets by the metal to metal seal between the piston rings and cylinder walls. Oil also squeaks past the rubber valve stem seals, and then past the metal on metal valve stems and cylinder head guides.
How much oil consumed can be directly related to the age of the engine. All the gaps between seals increase due to friction and wearing down the parts over time. Oil consumption is also related to how tightly the engine is built and how tight the original tolerances are.
Sometimes it's good to use a thicker oil as an engine ages. This can be beneficial to the engine because it keeps the oil where it's needed longer, and less oil will get burnt. As the gaps between parts (such as main bearings, rod bearings, piston rings, etc) increases thinner oil is pushed out faster and has less chance to lubricate. A slightly thicker oil can be considered such as 10w40, or even 20w50 on really old engines. Also, it wasn't until recently that engine tolerances were even made tight enough for 5w30 oil... 5w30 really needs tight tolerance between parts otherwise it will burn more quickly.
Very new engines will also burn more oil because when the cylinders are first honed the walls have a rough surface (as seen under a microscope). This surface allows oil to seep past the rings and into the combustion changer as the piston is pulled down the cylinder. When the piston strokes back up, the rings act like a squeegee and actually push this thin layer of oil lining the cylinder wall into the combustion chamber. Usually after about 600 miles the piston rings sand down the cylinder walls making a better seal.
I use whichever synthetic is on sale when I change my oil and I go one year or 20,000 miles between changes. I also notice that the amount of consumption varies and it seems that in hot weather more oil gets used. I burn a quart between about 1,500 and 5,000 miles depending on whatever and I have just under 70,000 miles in the engine.