Fuel Mileage questions

[fire8033]

I've post before about this and was unable to get any information that helped so with a little more information I am hoping to get some help. I have a 2004. 5 3500 Dually with 4:10 rearend. My fuel mileage is all over the place, I recently towed a trailer to Florida that weighed about 12,000lbs and was able to get 14 mpg, I unloaded the trailer and headed back and got 12. 5mpg on the way back. Once I was back I took another load that weighed about 9,000lbs and got 11mpg, I unloaded and on the way back got 16mpg comming home. This is mileage I put a pencil to and it was pretty close to the computer in the truck. This makes no sense to me, I would think under heavy loads the mileage would be less. I have taken the truck to 2 local dealerships and they say nothing is wrong, but then again if its not showing in the scan tool they are lost. I pressure check of the fuel system show no problems either. Okay guys any ideas????? Thanks for any help you can give.

 

[dhill]

I don't know how far you traveled, but it's pretty hard to judge milage by one tank at a time. You really need to average it over several tanks.



If you don't have the vent kit installed, you really can't tell if you filled it to the same point each time even though you see fuel in the fill neck.



My milage bounces around a bit, but it's the average that counts. My truck's mpg lifetime is 17. 3, but since I got the Smarty and loaded sw#3, my last three tanks are 18. 9 and getting better with the last tank being 19. 9. These are empty figures.



I have Spooled-up's vent kit on my truck.



www.innertruck.com



Dave

 

[GaryOwen]

I'd say that headwind/tailwind played a major role. I'm an RV transporter and have noticed that it is wind resistance that makes the most difference in fuel mileage, not the weight. Just a few mph speed difference can also make a big difference.



Sounds like your mpg numbers are about what I would expect.

 

[GaryCarter]

Ditto on the wind speed. 5 mph head / tail wind will mean more than a whole lot of weight change.



Gary

 

[fire8033]

Thanks for the idea's and responses.