Miles Per Gallon

My truck is 2010 Columbia LW.
Run around 55 mph on average
Average load wt is 39k
Average mpg 7.1
Mileage sucks in this truck.
dd13

 

First, fuel economy can vary as much as 30% due to driver technique - same truck, same routing, same GVW, same weather. Its not like you're back in a 4-wheeler.

Speed and tire rolling resistance are huge. One estimate I've heard and works fairly well is that you get 0.1 mpg increase in fuel economy for every mph that you slow down. If you're getting better fuel economy going faster than slower... you're defying physics - but most likely have a problem (leak) in your air-to-air.

Tires... lower rolling resistance equates to better fuel economy. Its huge. The few hundred you might save on a set of cheap high-rolling resistance tires, is dwarfed by the cost of the fuel you'll burn over the life of the tires. Tire pressure will screw with your fuel economy, so getting out there and dealing with the tractor tires is important. If anything, run them a little over-inflated - you're at risk of a blowout if they're underinflated.

Trailer tires are the most important position. A 2xxxx-series with 4 old drive tires on them that's dog-tracking will give you the worst mileage. I see as much as 1 mpg difference between a 2xxxx-series and one of the 110xxx-series trailers.

There are a million other factors involved... mountains, wind, road surface, fuel quality, etc. I see my mileage running from say 6.5 with a worst-case combination of trailer, speed, wind, etc to as much as 8.5 with a best case combination. I run at 55 whenever possible, progressive shift, stay off of the throttle, and set my trailer tandems to have about equal weight on the drives/tandems with the extra on the drives. You don't want to run with a tail-heavy trailer. My figures show about no more than a 1000 lbs nose heavy with a trailer equipped with duals, and maybe 2000 lbs on a trailer with wide singles. Somewhere in those ranges works for me. Keep your fifth wheel greased, and positioned to put the trailer as far forward as possible to keep the air-gap small. You want around 12,000 on the steers (or more if your front axle is rated for it) when you have full fuel and a load that puts you at GCVW.

Oh yeah... expect around 0.5 to 1.0 mpg drop-off with the winter blend fuels.

Now, back to the first part. Driver technique. Its huge. If you're getting really bad fuel economy - look at the way you're driving. If you're flooring-it to get onto the highway, running high rpms in climbs, not shifting up at lower rpms when light, running with the pedal to the metal when empty... what do you expect? Peterbilts are a little different than Cascadias, but quite a bit of it applies to both. So... get a notebook, and keep track of your fuel economy. Break down each trip into legs (say between P stops) and record your mileage and ECM fuel used. Figure the fuel economy. Another column for fuel economy for the entire trip. Then see how it reacts to roads, weather, hills. Try varying how you drive - but only change ONE thing at a time, and track it for a couple of weeks. Keep what works, toss the stuff that doesn't. You'll get better. When I started out my first Century showed a lifetime average of about 5.9 mpg. I got 6.2 out of the gate. Getting as much as 6.8 with a DD60 was about average... by working it I was routinely getting 7.5 by the time I turned the second one in. Good news - the new engines are a lot easier to get good mileage out of!

If you've got a turbo boost gage... drive by it, and not so much the speedometer. Keeping your boost under 10 psi in a Detriot will yield you great fuel mileage. You can't on the hills, but limiting it is good practice.


The Detroits are getting PM service every 50,000 miles, but it helps to get a fuel filter change at 25,000 - get your zerks and fifth wheel greased at the same time.