One of the FAQs on Royal Purple's website... http://www.royalpurple.com/faqs-motor-oil.html How often should I change Royal Purple in my passenger car? Royal Purple recommends following the manufacturer’s maintenance intervals while the vehicle is under factory warranty. In clean engines that are no longer under warranty, oil change intervals may be extended up to every 12,000 miles or annually, whichever comes first. Oil filter changes should be done as recommended by the filter’s manufacturer and oil should be topped off as needed. In dirty engines, Royal Purple recommends the standard 3,000 to 5,000 mile oil and filter change interval until the engine oiling system is clean and free of deposits left by lower quality oils and / or poor maintenance or mechanical problems. This will allow time to gradually remove existing deposits without overloading the oiling system. Mechanical problems such as fuel dilution, coolant leaks into the crankcase, poor air filtration and / or failure to maintain proper oil level are all detrimental factors to the service life of any engine oil. Any one of these factors can significantly shorten the useful service life of any oil. My questions are... Are there low quality oils out there on the market that are so bad that it wouldnt be recommended?