CM871 fuel mileage

[JimT]

I got a 2012 pete 587, 3.36 rears, 13 speed, mid roof pulling a 48 flat. At it's worst (not including the extra bad DPF death spiral time of nearly non-stop regens) I was getting 6's for mpg running 70ish all the while lugging the engine between 1350-1450 rpm. Back then (before I learned better, seriously, it's what I had been taught) I ran 1100 to 1500 rpm. Basically never went over 1500, though she complained under heavy loads under 1200 rpm. Back then setting the cruise at 1350 and 1450 rpm would produce then best fuel mileage, even up to the 8's at times.

NOW I know better. Once I'm out of the lower gears I keep it between 1550 and 1800 rpm. Rarely ever shift into top gear anymore as 68 mph is only 1450 rpm and I only run it there when empty on flat land with the boost 10psi or less. These days I rarely use more than 20-22 psi to climb hills. If my climbing speed drops below about 45 mph then the lower (10-15 psi) boost levels don't result in any better mpg's compared to climbing at 20-22psi while maintaining 45mph or higher. I'll "cruise" down the road with "foot control" engaged, anywhere from 55 to 64 depending on load and terrain, taking full advantage of gravity assists often rolling down hill with transmission in neutral.

It took me a while to get used to running at higher rpms and the different sound of the engine above 1500. But, after my inframe it sounded better and now that the rings have set it's really smooth and finally seeing fill-ups in the mid 8's again. Some of my worst fuel mileage these days is hauling lightweight roofing insulation (ISO). Tall and light with flapping plastic on the top, those loads average mid to low 7's (while loaded) from PA to New England mostly along the 84 corridor. Sometimes my ISO loads even drop down into the high 6's when there's high winds like we saw in March. Lots of additional factors when flatbedding.