I'll consider myself now informed on that DDan. But I'll bet quagmeyer has already made his decision. There are so many various opinions on this matter that his original question got a gazillion replies. I do not claim to be an expert. I learn something new everyday. But I know very general info about vehicles, and I will let the manufacturers deal with the specfics. So I'll keep following my owners manual and scheduled maintenance guide. I like to open as few cans of worms as possible.

 

5W-20 was to keep from getting fined for not meeting fuel economy and fuel emissions as outlined inthe CARB specs the government has put forth. All manufactureres have to show an improvement in both areas to conform to the CARB requirements. This was only due to a CARB requirment and has nothing to do with tolerances etc!!!! In 1998 Ford recommended 5w-30 and mid stream sent a recommnedation to all 1997 owners and newer to use 5W-20 due to CARB requirements. Nothing to do with engine requirements/longevity. The tolerance thing is only a myth!