Hand Calculated MPG's - Terrible!! What's going on?

[baycountry16]

So I didn't believe what the onboard computer was reading ( 10.9 mpg ) nor did I believe what my CTS was reading ( roughly 15-17 mpg's ), so I decided to hand calculate my mpg's on my last fill up using the trip meter. Well, trip meter read about 250 miles and I just added about 25 gallons of diesel. That is only averaging 10 MPG's. what the hell is up with that? Is it because I have a Crew Cab long bed ( heavier truck ). This is all primarily city driving miles and no towing. I've only had the truck a few months and just can't believe the mileage is this bad. Is there anything I can do to improve this? any ideas out there? Thanks in advance for any info

[Galaxie]

Winter Diesel?
Bigger tires?
Long idle or warm up time?

My MPG drops like a brick in the winter

[HankY]

have you calibrated the speedo odometer? By that I mean drive about 10 miles on a road with milage markers for the speedo hold a constant 60, for the odometer note the start stop milage for the milage covered. There are some calculators on the net which will help figure out the speed issue dont have one handy however. I changed tire size on my ranger and that is how I figured my speed and odometer error. When I fuel I have to add 4 miles to the total per 100 driven, the speedo is off by about 6 mph (slow). I dont know about the cts but if you have an navigator that gives ground speed that would be a good way to verify speedo reading for the route to be run.

[goXtreme]

I can usually keep the MPG's somewhere in the area of 18, (never more though), until winter hits, then BAM, I might get 12...MIGHT

[baycountry16]

Good to know. Maybe it's just the winter weather here in md


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[colinmitchell111]

What's your ect's? My thermostat was stuck open, put a new one in and my mpg went up 2-4.

[JumpinJack]

My last tank got 19mpg this tank down to 1/2 tank already and only 150mi. So I am assuming its probably the winter blend in it.

[baycountry16]

Ect's hover in the 188-192 range so I think thermostat is good


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[cyclonestroker]

City driving and winter diesel are probably the culprit. Your about right on par with what I get this time of the year if I'm unloaded around town.

[JohnO]

Big problem you face is these trucks are heavy, takes some juice to get them moving from a stop. So if you're starting and stopping a lot, it's going to burn some fuel. I see maybe 12-13 in town if I drive it real easy, 18-19 at a steady 60mph if the wind isn't up.

Winter diesel is cut with kerosene, you just won't get as good mileage with it, though I don't see a huge drop - 10-15% worse.

I've also found driving style affects mileage a lot more in the F350 than it does a car, probably due to the weight. The onboard lie-o-meter helps here. It's not the most accurate, but it's good to show you relative changes if you try a different style. Take it easy on starts, no more than 10psi boost, back off the power as soon as you think you might have to stop. I got my commute to work, some city mostly highway, from 12 to 17 by driving like that.

Punch it at least once a week, to work the variable vanes in the turbo so they don't stick. Just don't watch the fuel gauge, they really drink when cranked wide open.