Originally Posted By: JOD
Originally Posted By: Jim Allen
Whether or not you can see a change in MPG with heavier oil using the relatively inaccurate checking methods at our disposal, it is there nonetheless and over the course of years can add up. It's more an issue with engines that are short hopped and spend a lot of time in the warmup phase... which is the majority of engines these days. With a long, hot run, the MPG change due to one grade change is negligible.
I agree with everything you've written, but I'm not so sure about the above. With the function viscosity being >20% higher (hths 3.2 versus 2.6), I don't see how fuel economy won't be affected at full operating temp. I guess it depends on how one defines "significant", though...
Yeah, it's not a hill I'd die on without a lot of personal study or a good White Paper with controlled tests for study. Consider it more a general reference/observation than anything. I had 5W30 in my mind more than 10W30, though. I'm not sure the MPG difference could be seen within a margin for error. In a detailed study, maybe.
I'm doing this myself. I recently switched from 5W20 to a 10W30 HDEO in a Ford 5.4L V8 w/VCT. So far so good. I'm not doing this for any reason other than to simplify my oil stash across a small fleet of trucks, tractors, car and small engines. Making no claims that it's optimal. The car is a Honda, ironically, a 3.0L V6, but it's got a while left to use up my remaining stocks of 5W30 (which is was originally spec'ed for).