argo
04-12-2012, 09:50
As fuel prices continue to rise, and as my income continues to stagnate, I am looking for ways to improve fuel economy. As many of you know, I am able to squeak 27 MPG highway from my 6.2L 1993 Suburban. I am pleased with it for sure, but I want to try for more. One thing I am looking at is switching from Rotella 15W-40 to Rotella 10W-30. The 15W-40 is a conventional, while the 10W-30 is a synthetic blend. It meets all the diesel specifications that Rotella 15W-40 does, but it also carries the Energy Conserving designation that the 15W-40 and the 5W-40 Rotella Synthetic do not. I know that this engine in the 1980s was supposed to run a straight grade 30 weight (preferred) or 15W-40. Since at operating temperatures, a 10W-30 and a straight grade 30 are both 30 viscosity oils (SAE Measures viscosity at operating temperature) and the 10W-30 meets the API requirements for the 6.2 (it actually exceeds them), and since I have very healthy oil pressure now (25 PSI hot idle, 55 PSI at 1800 RPM cruise), is it reasonable to assume that I could safely run this oil in my engine, and perhaps pick up 0.5 to 1 MPG or maybe more? I know that thicker oil is not necessarily better oil, but I am a little concerned that the oil may be too thin despite the original literature for this engine calling for SAE 30. Cost is not a major issue, because it is only $3.50 more per gallon. Over 4,000 miles, I could easilly save more than that in fuel even if I only got 0.25 MPG more. So what do you think?