My 8.1L Sub has 247K miles.....drivetrain all original, and still gets 15-16 mpg freeway if I'm careful, and around 11mpg in city driving. That's not too far off what 5.3 and 6.0 Subs do. Uses oil, but that's not a big deal (to me).
I agree, I had a 2005 Silverado HD with a 6.0L for a while and the fuel economy was not much different from my other Silvy with the L18 8.1L. Add a car trailer behind the 6.0L and it would actually consume more fuel than the big block.
Yep, some L18 8.1L’s like their oil. My 2001 Silverado HD has used a quart every 1,200 to 1,500 miles since I bought it new but I have not performed any of the GM bulletins to address its oil habit. On the other hand, the 2003 L18 in the 1978 K10 does not consume any oil between 3,000 mile oil changes. Prior to installing the L18 into the K10 I performed the GM service bulletins to address oil consumption by replacing the intake manifold bolts to larger shank bolts to prevent oil vapor from being pulled into combustion chamber through the intake manifold as well as installed the newer design 89017539 intake gaskets. The bolts and gaskets must work, like I mentioned above….it doesn’t use any oil.
Your ’05 L18 would already have the new design intake bolts but may not have been built with the 89017539 gaskets. If you ever have the intake off definitely replace the intake gaskets. This new part number supersedes all older intake gasket part numbers. There are inexpensive too, like $40 for the set. The intake gaskets are easy to replace as there is no coolant passing through the intake and many times you can lift the intake up enough to replace the gaskets without needing to disconnect the fuel lines. Actually yours only has one fuel line as they went returnless in 2004.
