[Ford Man]

Changing from 10w30 to 0w30 isn't likely to net any noticeable mileage benefit. The only difference in the two weights is the cold start viscosity. One acts as a 10 weight on start up, the other acts as a 0 weight on cold start up and they both act as 30 weight on a fully warm engine. I've never used synthetic, but if mileage gain is all you're looking for in the change from conventional to synthetic it wouldn't be worth the extra cost associated with synthetic. I think the money would be better spent on giving your car a tune up. Personally I've never had any problems with conventional oil in about 1M miles of driving, with one of my cars being at 518,700 miles on the original engine. I run 10w40 in my '88 Escort and have a lifetime average since I started my gas log on this site of just over 41.5 MPG combined. The old highway EPA rating on it is 42 and the old combined rating is 37. Adjusting driving habits will do much more for fuel efficiency than changing to another weight oil.