Originally Posted By: FZ1
Thanks for you response. I was just letting the Honda dealer do the oil changes so, who knows, they could have been using 5w30 so when I started using 5w-20 synthetic the vicsosity change could account for the difference. I just happened to get slightly better mileage with the synthetic immediately. Good math skills, 20-21 is correct.
FZ1 for what it's worth I still haven't been able to find any good documentation on the real efficiency differences between oils. Lots of claims from oil manufacturers, both RP and Amsoil have claims on at least some of their oils that seem very high, but I don't see anything more objective. I did learn that the old Energy Conserving and Energy Conserving II standards were for 1.5% and 2.7% improvements compared with a reference oil, but I think the reference oil was of a different viscosity so that doesn't say much about improvements within a single viscosity grade. The only references I see about the current Energy Conserving spec is that individual users may not see any difference at all but that there should be a savings across the entire vehicle fleet. Well, ok, that hardly says anything useful.
I bet JAG has something on this in his seemingly vast library of oil references, maybe he will see this thread and see fit to post something.
I'd be very pleased to be able to get, say, a 2% improvement in efficiency from oil. It does all add up.
