Been driving the same daily for eight years, always synthetic oil as the manufacturer requires it. I know my car very well after 135K miles. After the factory stopped my no-charge 5-30w synthetic oil changes, I started using Mobil 1 fully synthetic 0-40. Didn't noticed any difference over the factory synthetic oil. By 100K miles my engine would burn 1 quart of oil per 7000 to 8000 miles. Then I switched to a off brand low grade 5-30w fully synthetic to save money and noticed quickly that engine would burn that 1 quart by 4000-5000 miles. I switched back to Mobil 1 0-40, and I'm back to 7000-8000 miles before I use a quart. Whether the slight weight in the two oils made the difference or the quality, I don't know. If I shop around I can get a 5 qt bottle of Mobil 1 for abt $25, not too bad considering the mileage I get from it.