I have a 2004 Nissan Sentra SE-R Spec V 2.5L 4 banger. At 1000 miles I changed the oil with GC 0w-30 and then again at 3000 with a Nissan Filter. At 5000 I switched to Exxon SuperFlo 5w-30 because my mileage seemed crappy 26 MPG. Now with the Exxon I am getting about 28 MPG. Is this oil good enough for my new engine?