I have a mpg question !!!!
 

I need for somebody to riddle me this:
What would be the MPG for a '11 Prostar with the following specs????
ENGINE: CUMMINS
HP: 450
TRANS: 13 (FULLER)
REARS: 3.58
CRUISE: 70mph
PEDAL: 75mph

running that fast, probably 6-6.5 mpg.


Slow I down to 65-67, you'd likely see closer t 6.5-7.

It's mostly depends, who is driving...
http://i6.photobucket.com/albums/y213/solo3793/cat3.jpg

I just had a 1.3 mpg improvement all because of a stupid sensor on my truck. So while I will agree that a driver can't be ruled out, equipment issues can mask what you THINK is a bad driver.

It doesn't specifued "stupid", unwilling, unskilled...and yes, it could be stupid. And of course you got to make sure it's ok mechanicaly.

For close to 22 months everyone's answer, including mechanics were for me to slow down and change my own driving habits.

My gut always told me there was something wrong with the engine but no one wanted to believe me. The term "stupid" is a term of endearment after so long of trying to figure this out.

I tried running my ISX at different rpm's and I found that it makes the best mileage at 1650 no matter how much is in the back, unless bobtailing. I averaged 6.5 with idling every night and running 70mpg, but that was a 10 speed Century with 3.25 gears in the back. The Prostar will beat that all things being considered. The ISX 450 only makes 400 hp on the dyno, and that's the best case according to Cummins. The rpms are critical on that engine. You cannot run it slower under load and make more fuel mileage because you loose torque.......If it's a used truck I'd make sure the ECM hasn't been programmed for a reduction in horsepower, which is common for trucking companies to do. Less than 400 to the wheels is not enough for a loaded truck in my opinion.

There are a few trucking companies that bought into the idea that you could run an engine slower for more mileage, but these are Cummins engines, not Cats, and the manufacturer warned them against doing this. Lugging these engines will hurt them, yet you'll see companies recommending just that. My fuel manager at one company used to always quiz me as to how I got the mileage I got when he'd run company trucks at 60mph and couldn't get that. I told him that as long as you make a truck slow down for a hill, limit the horsepower, and ignore everything the manufacturer is telling you about the rpm that the cam is ground to operate at, then you'll never figure it out. If they want to go that slow then they'd have to gear the truck accordingly......

The most important factor to getting better fuel mileage is the driver. Gearing, terrain and other factors also contribute, but the driver is the one who controls everything. If you keep your truck running around 60-65 mph, you should see better fuel economy than running 70-75 mph. Constantly speeding up and slowing down will eat into your fuel consumption. If you maintain a steady speed that will also help. I have an older International that has consistently gotten around 6.29 mpg. If you keep your speed down, drive right you should be over 6 mpg. In fact, you should be at or better than my mileage on the old International. You can take two drivers who drive the same truck and get different mpg. Without knowing you or how you drive it would only be speculation to tell you how well you will do on mpg. But, I would expect something around the figure I noted above. If you check the ECM, you could find out how well the truck has done with other drivers. Keep in mind that the ECM will usually be a little higher than actual HUB miles you calculate from the truck odometer.

i've been thinking about this a lot lately being that I hope soon to be getting a glider and trying to figure specs out. low rpm's don't mean best mpg. here is where my take is on it. every truck has a perfect spec. for example. if you get a older s60 Detroit in my opinion if you spec it as you would with a cat let say.. low pro 24.5's, 13 speed and 3.36 gears the cat will out run and preform the Detroit. and I'm betting the fuel milage will be about the same. that would be a 550 cat v a 500 Detroit. but... if you do same truck with 3.55's I bet the Detroit will surpass the cat by far with fuel milage. again.. its my take. it seems detroits like more RPM's for fuel mileage. but to be contradicting.. my truck is a 10 speed, low pro 22.5's 435 single turbo cat and 3.73 gears. my truck at 60 or 70 same mpg. it don't change. 75... she'll nose dive.. FAST. on flat ground I can easy get mid 6mpg at 70. that would be with a load like 30k. when I'm at gross she'll get 6.25ish anything under 30k she will get over 6.5 but not much.

like said before its all in the driver. I use every gear no matter what. I also shift at 1500... max. when I pull a hill I kick the cruise off and don't stand on it. when I pass I don't stand on it. I am anal about my maintance. every 250k the truck goes in to cat to have the overhead run. (though last time I think they did something being it just isn't running the same.). my oil is changed every 15k, once every 6 months a bottle of FPPF in the tanks, every 2/3 months some lucas in the fuel. the biggest thing that I've seen was having the charge air cooler checked. another one that I didn't buy into but learned.. the hard way.. tires. I had cheap arura tires. LOVED them. swapped them out for a set of sampsons that I got at the TA for $2400. I can not stand these tires. again.. this is all my take. could be wrong but its what works for me.