I recently went from 10w30 to 15w40 and have seen some improvements in several engine area's.
I haven't been into the bottom end yet but the head has been totally rebuilt with the exception of the rockers and push rods.
Improvements I've seen w/the thicker oil:
1) Higher oil pressure. With the 10w30 the oil never got to 15 psi. I would gestimate 12 to 13 psi max.
With the 15w40 the oil idles @ 15 psi and I'll estimate 17 to 18 psi @ speed.
2) The engine it quieter. Theres less valve train noise and no bottom end noise.
Neither oil produced any smoke and engine temps were about the same.
I'll be closely monitoring the engine come colder temps as this will the my 1st winter w/the truck running. I'm not adverse to changeing to a thinner winter oil if necessary.
For warm/hot weather temps the engine seems to run much better w/the thicker oil.
Dave
