So here's a little info on the truck at hand:
2003 Freightliner Columbia 239 WB
S60 12.7 370/430---Currently set at 430/430
Eaton Single OD 13 speed (.85)
2.93 rears
22.5 LP's

I pull intermodal, it's cheap, heavy and a pain in the ###. I drive 65 everywhere. That puts me at 1400rpms's +/- and seems to run/pull well at that speed. Problem is, I only seem to be getting around 6-6.25 mpg. When I drove a company truck before, pulling the same freight, weight and route with a much weaker lower geared truck, I'd average about 6.5-7 mpg. It was a Volvo daycab, Volvo D12 385hp, 3.90 rears, 10sp OD (.74), Tall 22.5's. I usually went 70mph which was about 1700rpm's. It was their fuel right?

So my question is, what if I were to turn the power settings back down to 370/430, or to 370/370 for that matter? Does 60 hp really make that much difference? From what I've learned, HP doesn't exceed Torque until 5252rpm's. And I'm pretty sure the truck will never see that. So what's the point of having the HP upped if the torque doesn't change at all? I'm just trying to find a way to save a little cash. .5-1.0 mpg could save me about 250.00 per week.

Thanks

 

MPG has a lot to do with gearing and aerodynamics along with the driver, of course. If I were you I would get in touch with a dealer or Detroit distributor and pose the question to them. You may be using more fuel due to the higher gears and weight. If you changed your gears to something around 3.55 it might help you do better with the heavy weight. Like I said, I would check with a dealer and ask them.

 

If I changed the gears to 3.55 it would be a rev monster. Note that my transmission is a direct drive 9 speed that was converted to a 13sp. The top hole is only .85 as opposed to a regular 13sp with a .73 top hole.

 

m.p.g has so many factors. I have a 11.1 det ser 60 350 h.p. I get easily 6 & can get 6.5-7.0 m.p.g most of the time. 1400 rpms @ 55mph 1850@ 74 mph I can get 6 mpg at 1850. I have a cabover, so you would think with the shape of the truck, the low hp engine & the high rpms, that I would not get the mpg I get but I do. though my truck has a very short wheelbase 150'' so my trailer is so close & does not get any wind drag. I also get better fuel mileage with hiwy tires rather than lugs. a huge difference there. though I am still not sure why my truck after 1.3 mil miles with no major work done to it ever beats new trucks om m.p.g.

 

After talking with the guys at Detroit, I think my first move is to get an overhead done, and then go from there if things don't seem to get much better. He also said I may have one or two "tired" injectors...That's all I need.