Originally Posted by Patriot Services
Oil is not changed because it is dirty. Either the additive package is depleted or it failing from thermal breakdown.
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Exactly. If your oil is truly getting "dirty" you actually have other problems. Synthetic is much less likely to break down prematurely due to the heat, and with air cooled engines this is a very real problem.
Extended oil changes in cars is real, but you have to be cautious about them. In relaity you can, but you really need to get your oil tested, an oil analysis, to be SURE that it's still working. In a car or light truck it's not really that cost effective when you are talking about 5 or 6 quarts of oil. And MOST newer vehicles do NOT need the oil changed every 3 months or 3,000 miles like has been ingrained in everyones heads for decades. Even with conventional oil most manufacturers are calling for 4 to 7 thousand miles between changes. Look at the recommendations from your vehicle mfg. before assuming.
Semis and big engines like that can really benifit from extend oil change intervals, but they are also using bypass filtration systems and oil analysis. MANY are going a million miles on the same oil with just topping off periodically. It's true...