My sister lives in Mooresville, NC and her next door neighbor is a mechanical engineer for Hendrick's Motorsport. I ask him about auto maintenance.
First and foremost go with the owner's manual. The factory know what is required for maintenance. Never take any mechanic or garage advice as to how to service your vehicle. If there is a normal and severe schedule, use the severe schedule if you are not sure.
As for oil change, garages make more money on 3,000 mile schedule. Use the schedule specified by the owner's manual. Normally 7500 miles on most new cars. Take a note at the oil weight on the manual. The new cars use 5W-20 weight. To save gas. Many new cars now are filled with synthetic lube. Not only in the engine but elsewhere such as transmission and suspension joints. Normally the factory will specify a longer interval such as 10,000 or even 15,000 when using synthetic lube.
For older cars and trucks with over 150,000 miles. If you see you oil pressure drop or some smoke out of the exhaust or smell oil. I was advised to switch to a multi-vehicle oil such as Rotella. Walmart has their brand and far cheaper than Rotella. You should see the oil pressure go back up and the oil consumption go down. The extra additives will also clean the engine of any sludge.
Never use additives. They are a waste of money and some will actually damage your engine. There are additives that are nothing more than mineral spirits. They dilute your oil and do more harm than good.
Engine flush should never be used. If you change your oil as scheduled, there is no need. If you really think you have engine sludge, the best way to remove it is to drop the oil pan and clean it out.
It all makes sense.
