I have been running Valvoline conventional 10W-30 in mine for 11 of my 12 years of owning it (106k-200k miles). Last year, I went to the same oil, in 5W-30, and I noticed slightly better fuel economy. My local Walmarts stopped carrying that oil (or maybe Valvoline stopped making it), and now they sell the same thing in a synthetic blend, so that is what I now use, in 5W-30.

For me, the only reason I would go to full synthetic is because of the longer intervals between changes. Because of that, it probably works out to a little less money per year, even though full synthetic is more expensive. Plus, much less time is spent on oil changes, because of the longer intervals.

There are lots and lots of 300-400k+ engines out there that have run regular conventional oil all of their lives, so I would never switch to synthetic for the only reason being that my engine may last longer. Any vehicle of mine with 300-400k on it would be completely ragged out, and I wouldn't want it anymore, even it if the engine still ran like new.

I don't care what anyone says, though - I would never go 10k miles between changes. My wife's Civic requires full synthetic, and its oil is black and looks real old at 6k change intervals. 6-7.5k is the most I would ever go, on any full synthetic oil, despite what some people say.