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2015 350 XLT with 3.7 L/3.73 rear.. horrible mileage

13302 Views 27 Replies 14 Participants Last post by  ranxerox
First of all, we do live in WV so there are some hills around here, so I expect *some* decrease from the 19 mpg highway estimate. However, I'm getting a hand-calculated 13.7-14.2 around here most of the time with an 80/20 split of highway/city, respectively.

Van has 35,500 miles on it and the only thing that's not stock is the tires... currently running 225/75/16's instead of the 235/65/16's, so it's a 4% increase in tire size... that only equates to around 85 rpm at 70 mph, so it's not much. I had to change them out after we'd had the van less than 2 weeks because the stock tires started showing cords and throwing chunks of rubber off of them at 34,500 miles.

Anyway, I talked to a guy from church today who has basically the exact same van as us with the same amount of people to haul (and drives the same route to get home), and he's getting 17-17.5 average, so around 20% better mileage. I have no idea what's going on with this thing.. There's no CEL showing, so it doesn't appear to be something so big the computer is fussing about it, but I can't imagine that mileage being anywhere near normal. If I keep it at 45 mph around here on the side-roads I can get a decent mileage reading on it if I reset it and run a few miles, but once we hit the highways and actually have to GO anywhere, the mileage drops like a rock. I don't ever even push it past 72 or so, either, so it's not like I'm running it hard.

Any ideas? Going to try to get it into the dealer to run a diagnostics on it for the awful mileage this week, so hopefully that will shed some light on it. I'm just about ready to trade the frustrating thing in for an ecoboosted van, though, as at least those have a decent amount of torque to get up the hills.
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Here in western North Carolina, our van averages around 15-15.5 taking it fairly easy, empty in combined driving on local roads. The computer thinks we do better by about 1mpg.

With your tires, you are traveling more miles that your odometer tells you, no?

Otoh, on the highway we see 17 with out too much problem. Wind and hills determine 16-18 in general. Try to stay around 70. Sometimes 80 but takes an economic hit there.
I'm adding this from the road. Van loaded with two motorcycles and camping / riding gear / extra battery/ arb fridge etc. Knoxville,tn to Crown Point Indiana cruise set to 72 - 73mph and just go. 18.6 computer milage - 17.56 calculated. Ac on full tilt. We are still on the second tank, nearing Wausau, WI and computer is telling us 17.9-18 with intermittent head wind during the trip, blowing hard here now running a little faste today too. This is somewhat better than we get in the mountain driving conditions but I feel is typical.

Our friends Sprinter is also a 22 mpg thing. I can buy one **** of a lot of gas for what I saved vs diesel though... We sold a f350 power stroke to get this van and I like filling anywhere I want. I also anticipate lower maintainence costs.

You may well have an issue with the milage you are getting.

Hope this information is relevant and helpful.
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