laknox wrote:

Since I haven't yet towed with the '22 3500 Denali, does the L5P have a "sweet spot" like the older Duramaxes do? My '02, when towing, seems to have a sweet spot right about 62 mph, max. I lose 1-1.5 mpg towing at 65. First tow will be in 2 weeks, so I'll see how it goes. I'll stick with 65 and see. Endurance tires are 81 mph rated, so no issues there.

Lyle

4x4ord wrote:



To loose about 1/2 mpg due to increasing your speed from 62 mph to 65 would be expected on account of the increased drag. Loosing more than that would be from the engine running at a less efficient rpm. But, increasing an engine's rpm by 5%, so say from 1500 rpm to 1575 rpm) you sure wouldn't expect to see its efficiency drop by 5 or 10%. Two basic rules that apply to fuel economy are:
1. a diesel engine is efficient at making power when loaded heavy .... higher rpm at a lighter load costs fuel.
2. turbo diesel engines tend to be most efficient at about 1700 rpm.
So although a heavily loaded engine might be most efficient at 1700 rpm a heavily loaded engine at 1300 rpm might be more efficient than a lightly loaded engine at 1700 rpm.