bad mpg what to do?

1999 KW900L, 505 HP, 13 spd, 355s' I think.

 

ok something I had learned along the way, there are times playing the fuel game can actually save your butt!
I drove a pete 387 with twin 250s and kept them full until I realized a gallon of diesel weighs 8.73 lbs every 100 gallons
equals 873 pounds , every 1000 pounds equates to another % of mileage lost.
its a matter of set cruise, keep your speed within the parameters of your gear ratio
horsepower will kill fuel economy, if your over set for your truck.
go online find the specs for the truck/set up you have (ratio v.s. recommends)
run within those specs , if the factory set up was 3.73 finals @ 425 h.p. for 73 mph, then at 75 mph youre cooking 1/3 the fuel for nothing.
also you might consider running a mpg at factored speed equation, I have and found with my Coronado set to 475 h.p. 72 mph @ 1550 I get 7.0
at 67 mph I get 7.2 to 7.4
at 64 I get 7.8 average, pulling a flat bed 53 foot with 45.500 on deck . my experiment was done across 500 miles , 68 to 80 degrees with humidity between 70 t0 85 %
(according to weather channel).
but all variables aside, what the factory built the truck at spec wise will determine your parameters

 

Some cab over. LOL. I'd run it at 1450 you know from driving it and have said so already that it seems weak at anything lower.

As far as what gear:

A13 speed transmission is running an overdrive gear and a direct gear to get the top gear ratio. In 12 it is running an overdrive and an underdrive to make the gear ratio. This produces more drag so it should take more energy to drive like that but you'll be going slower and possibly in a more efficient RPM range as well so that should offset it.


12= 1450 @ MPH is that right ? Give or take?

Published numbers say OD vs Direct costs 3-4%. However it seems hard to nail down 3-4% of what. Some think it's overall fuel economy. I think it's 3-4% of the energy required to turn the transmission. It takes about 20 HP, IIRC, to turn it. So that would be around 1 HP.

 

AlabamaZig : So it is still "slower speed = better mpg". I can't drive this truck at 55mph, it just won't. At 65mph I'm getting 5.0mpg. Your advise please ; 55 in 12th at 1500rpm or 60 in 13th at 1350 rpm and constantly downshifting for grade?

 

Constantly shifting will waste fuel. I'd run at 1550 before shifting all the time

 

If you can stand to run 55 try that in 12th gear for a week or two and see what the mileage does.

 

if you have a 2013 cascadia with dd15 475 hp, 13 sp, 3.58 diff, newer aero fairings, speed btwn 65-70 mph, get loaded 20-30k lbs, what's the average mpg then?

 

Freightlinerbob: Started out in two different cabovers. Loved 'em, but out grew them. 12th gear at 55mph is 1500 rpm. 13th at 60mph is 1350rpm and weak. Thanks!

 

The dealer he bought the 2013 cascadia claimed to be a 7 mpg truck. Some reason his mpg got worser and worser.

 

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