What do those cryptic number-and-letter combos on the oil container mean? Does it matter whether you use 10W-30 or 5W-20? Can your car really tell the difference between conventional oil and synthetic oil? I mean, c'mon, it's engine oil not Cabernet Sauvignon. Fact is: It does matter. Not only can it affect the amount of wear and tear on your engine, if you use oil not recommended by the manufacturer and a problem results, your warranty may be voided. Follow the link below for advice on ensuring your vehicle run like the well-oiled machine it should be.