Unlike transmission, power steering and brake fluid, engine oil has the added responsibility of removing soot and dirt from inside the engine. A transmission is a closed system, meaning it does not have any way for dirt and debris to enter its interior. An engine, on the other hand, is relatively wide open to dust, dirt, pollen, water and of course, engine exhaust. While gaskets and piston rings do a diligent job keeping the engine cycles independent of each other, exhaust, soot and outside dirt inevitably finds its way past the pistons and into your engine's crank case.
Because cleaning is one of the principal duties it takes on every time the engine fires, engine oil has a life cycle. Have you ever looked at used engine oil and wondered why it's black? The simple answer is soot and dirt. Engine oil contains additives and detergents within in its ingredients that effectively carry away all that grime. Think of oil along the same lines as blood in the human body. While blood carries oxygen throughout the body to all the different organs, oil cools, lubricates and carries away dirt. The black color that you see is actually all that grime trapped in the oil. While some synthetic oils can still function while they're relatively dirty -- thus the extended time between synthetic oil changes -- there's a limit to its cleaning capacity. It's for these reasons that lifetime engine oil is simply not practical.
Heat is another factor. Engines can reach temperatures well in excess of 275 degrees Fahrenheit (135 degrees Celsius). Those high temperatures tend to change the chemical composition of oil. Synthetic oils handle heat better, but conventional mineral engine oils break down at high temperatures and lose their original chemical composition after repeated use. Traditional thinking always said you should change your engine oil every 3,000 miles (4,828 kilometers). With synthetic oil, you can go much longer between oil changes. For instance, BMW recommends an oil change every 15,000 miles (24,140 kilometers) for the MINI Cooper.
For now, the closest you will probably get to lifetime engine oil is by using synthetic oil. Synthetic oil differs from mineral or refined natural oil in many areas -- including cost. Expect to pay three to four times more for synthetic oil. But remember, manmade oil will extend the period between oil changes. Pure Power Inc. sells a lifetime, washable oil filter for about $199, or roughly the cost of 40 disposable filters; however, that only solves the filter portion of the equation. The bottom line is that you must still change your oil on a regular basis -- at least for now, anyway. Oil is the lifeline of your vehicle's engine. Be sure to manage it as such.
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