I have a 2002 Nissan Maxima with a 3.5 liter engine and six speed transmission which I purchased used with 28K miles. I have all the service paper work from the previous owner and can see the dealer changed the oil every 5-6K miles with Pennzoil 5w30. My goal was to have the car running on Mobil 1 at the 30K OCI. For the next 2K miles I watched the oil level to make sure there wasn’t any oil consumption and didn’t notice any measurable change on the dip stick. At 30K I switched to Mobil 1 5w30 with OEM oil filter and installed a new PCV valve. After driving the car for 1300 miles the oil was down .25 of a quart. This trend continued for the next 10K miles. My thought was this engine just doesn’t like this particular oil or synthetic in general. I put Havoline Conventional 5w30 oil back in at 40K and have still noticed some oil consumption, ~ .5 quart in 3k miles. My question to the oil gurus is this, why does my engine continue to consume oil after going back to conventional oil?