Modular engines must use 5w-30, and pre modular engines should use 10w-30. It's really that simple. I haven't seen one single '96 or older Ford truck run better, start faster, idle quieter, etc. with 5w-30. In fact, every pushrod engine I've seen 5w-30 go in started with a mild but brief knocking.

Take care,
-Chris

 

Cosmo this was explained to me by a Ford Tech. Bearing clearances are no more tighter today than they were 30 years ago. Motor oils no longer break down into lower viscosity grades due to normal heat so the 10W-40 and 20W-50s are a thing of the past for passenger vehicles and light trucks. If one lives in extreme cold climate a 5W-20 is perfect and if you live in a hot climate 5W-30 and 10W-30 are perfect. Ford specs the 5W-20 and 5W-30 to meet emmisions and cafe standards only, I live in South Florida so I use 5W-30 instead of the 5W-20, you actually get more protection from a 30W than a 20W oil. He also said that in the owner's manual 5W-20 is preferred and not mandated so Ford can't legally refuse warranty claims.

 

Thanks everyone for the input, I just get curious about these sorts of things I guess because in the past motor oil was just motor oil. The technology of it all today is fascinating.