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MPG with 3.21 gears

7K views 26 replies 19 participants last post by  Thunderhorse 
#1 ·
What are you guys seeing for gas mileage with the hemi 8 speed tranny and the 3.21 rear end? I do about 80% city and 20% highway driving and I've been keeping my eye on my average mpg due to it being fairly low than what I expected. I'm going on 1500 miles on the truck and right now it says I'm averaging 14.4mpg.

I used to have a 2005 Ram 1500 with the hemi and the 3.92 rear end and I averaged 15-16mpg doing the exact same driving. So now on the new one with the MDS technology and 8 speed tranny I expected to be getting more gas mileage.

Any input?
 
#2 · (Edited)
Since you're 80% city (stop and go) 3.92's would probably produce better mpg due to easier starts.

Although I think the 8 speed 3.21's have a better starting gear than the 2005 3.92's. So it's probably just due to the fact that the old truck is probably lighter and broken in. My mileage got better after a while.
 
#3 ·
I was thinking it may have something to do with break in. Just kind of odd to think you have to put a lot of miles on a truck before it gets optimum gas mileage.
 
#5 ·
Eight speed with 3:21 axles and a Hemi.

Currently I'm seeing 19.7 average, that is down from 21 average using summer fuels (which have more energy than winter fuels). My driving is boulevard with synchronized traffic lights and freeway with some stop and go.
 
#6 ·
2013 Ram 1500 V8. 3.21 gears 8 speed transmission : I do mostly city driving (computer says average miles per hour is 19-22 per tank). Hand calculated mpg is 12.7. Truck is currently all stock. I have 2300 miles on it since the end of August. Tire pressure is at 40 psi.
 
#7 ·
I finished that tank of gas I was currently using and switched to a different stations fuel using the regular unleaded (87) gasoline down here in Texas. My MPG instantly went up 2mpg according to the trucks display.

I'm in no means worried about the fuel economy...if I was worried the truck wouldn't be getting the 35" M/T's and 6" suspension lift put on Monday lol, I just thought what I was getting seemed a little below average.
 
#10 ·
I have 3.21 axles with 7600 miles on it. I have got no worse than 16.4 MPG and my avg is usually between 17-18.5 depending on how cold it gets. I have got 23 on the highway before but I was unloaded and had a tailwind.
 
#11 ·
My overall average on my 3.6L with 3.21 gears (Crew Cab, 2wd, SLT) is 23.4mpg. That's 3903 miles and 166.97 gallons since I started keeping up with it. I use an app called "Gas Cubby" to track my spending. It also shows your best and worst mpg tanks, and data like "average cost of fill up, miles per dollar, and miles per fill up.

If you're a nerd like me and keep up with those things, this is great.
 
#14 ·
I believe that the 3.21 turns 1500 RPM at around 67MPH, so for best mileage I keep it around 65. On that note, you can put up some pretty impressive mileage numbers around 45MPH on rural roads that have low speed limits and not a lot of stops.
 
#18 ·
Well before my lift, wheels, and 35" tires I was seeing 18mpg...lol so I was expecting it to drop. Now I'm seeing 13 if I'm conscious of it and 10-11 if I'm not. It sure does look damn good though!:smileup:
 
#19 ·
2013 5.7 8-spd HFE R/C shortbed tonneau cover 2WD 3.21 17" tire 1300 miles on odo

my first & only trip in the truck:
just over 200 miles, on the way back from the dealership,
4-8 degrees F, 2-lane roads, cruise on 63 most of the way...

22.1 mpg according to EVIC

tire pressure according to TPMS all 37-8 so each is couple psi low.

I drove *very* conservatively :)
 
#20 ·
I just got my 2013 - it was a demo with 4500 miles.

Crew, 6-4 bed, 4x4, 8-speed, 3.21.

Pure highway, 21.5ish. Commute, which is about 50-50 hwy/city getting pummeled around 13.5-14. Weird. Not sure how the demo was driven, but hoping it comes around.

I've been light-footing it for the most part too, so I'm a little surprised.

Winter gas, cold and crappy Goodyears not helping.
 
#26 ·
Horrible mpg!!!!!

I have a 2010 dodge ram 1500 w/ 35" M/T tires and my truck gets horrible gas mileage. I drive mostly city-short commutes to work and get 8.2 mpg through a full tank of gas. I hardly ever get on it and keep it a goal to try and keep the “eco” light on. I burned through half a tank of gas down the freeway yesterday and got 13mpg. Now I bought the truck with 325/65/18 tires (about 34.6” X 13” wide) and a leveling kit so I know the mileage should be 2 gpm worse or so but does this sound right?? I just put 24” magnaflow duals on it and Im saving up for a CAI. It has the stock 3.55 gears in it. Im wondering if I would see a few mpg’s better going to 4.10 gears? I know its a truck and can see getting 11 or 12 mpg city but don't know how much longer I can do 8 mpg! :doh:
 
#27 ·
I have a 2010 dodge ram 1500 w/ 35" M/T tires and my truck gets horrible gas mileage. I drive mostly city-short commutes to work and get 8.2 mpg through a full tank of gas. I hardly ever get on it and keep it a goal to try and keep the “eco” light on. I burned through half a tank of gas down the freeway yesterday and got 13mpg. Now I bought the truck with 325/65/18 tires (about 34.6” X 13” wide) and a leveling kit so I know the mileage should be 2 gpm worse or so but does this sound right?? I just put 24” magnaflow duals on it and Im saving up for a CAI. It has the stock 3.55 gears in it. Im wondering if I would see a few mpg’s better going to 4.10 gears? I know its a truck and can see getting 11 or 12 mpg city but don't know how much longer I can do 8 mpg! :doh:
The width and tread pattern of your tires along with short city trips is what is killing your MPG. Those tires are about 20% wider than stock so they have much more rolling resistance. 4.10s may help your mileage butI wouldn't expect more than 13 MPG if that.
 
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