You're not going to wear your engine out faster with 5W-30; in fact the viscosity is theoretically the same as 10W-30 when warm.
Keeping in mind that most engine wear occurs in the first few seconds of a cold start, the thinner oil may actually give you a longer engine life. The lubricated internals of an engine - sliding surfaces running at hundreds or thousands of feet per minute on a thin film of oil - have a different perception of "thin" than you got while pouring it out of the bottle. Lastly, the folks who determine those viscosity/temperature charts in the manual have a darn sight better and more relevant education than a highschool diploma.

Based on the owners manual, for your location 5W-30 is ideal for year-round use.

There is a recent news item from Ford that they are moving to a 5W-20 for all locations. Based on that and the past-decade more common use of 5w-30, it seems manufactures are learning that thinner oils are more beneficial overall.



[This message has been edited by *paul (edited 07-19-2001).]