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Fuel Efficiency vs Rear Axle Ratio

Aside from looking at Fuelly data it's a bit of an unknown. The 3.21 theoretically gets better mileage, but the 3.92 allows MDS to kick in more often potentially erasing much of the 3.21 advantage. Also depends greatly on how heavy your foot it, how fat your Ram is (payload erased by option weight), and what kind of terrain you normally drive through.
 
Lots of recent threads on this. Just yesterday we hashed it out again. The 3.21 is considered the mileage gear. 3.92 is considered the power gear.

So how you use the truck and how you drive are what affect mileage.

One can actually get better with a 3.92 than one with 3.21 and a 3.21 can tow just as well as a 3.92.

The new transmission really makes this all about you.

But for reference...the max tow has 3.92 and the HFE(when it is released..High Fuel Efficiency) will havethe 3.21

Mileage will vary based on trim, climate, season, terrain, driving habits, idling periods, etc.
 
I have the 3.92 and my MPG is crap and I dont even tow. I am currently averaging 12.9 mpg
 
I have the 3.92 with 5.7 Etorque and if I drive it like I want to (more aggressive than average traffic) I get 12-13 City and 17.8 Highway. If I drive intentionally trying to keep the Eco light on, 17-18 City and 19-21 highway. 21 is at 60mph. 19 is at 70. 17.8 is at 78.

If I lived in flat country, I could get 24 cruising at 50 mph. Max economy seems to be around 1250 to 1400 rpm with the Eco light (MDS) on. MDS will not engage above 60 except downhill.

I have a fully optioned Limited 4x4 with Offroad Package. I keep it in Aero mode which I believe is still 1" above Aero on non-Offroad Package trucks. My truck weighs 7100 pounds.
 
Ive got a 3.92 in mine and it fkn sucks gas ... City 12 to 14 ( 14 if I'm light on the pedal ) hwy maybe 16 if im lucky its pure **** and I have already called several dealers to see about a bigger tank, im usually at the pump every 5 to 7 days and they said I'm out of luck no way to change to computer to read the size of tank I want complete ********
 
I have the 3.21 and I'm averaging 18 MPG on the current tank. Only have 600 miles on the truck though.
 
These threads are popular, for sure. I’ll be updating the MPG sticky as the V6 etorque rolls out. Looking at previous model years on Fuelly clearly shows the 3.21 has an edge, but not by a large margin. It takes time to go through each truck, as only engine options taken into account on the aggregate data.

At this time I am averaging just over 20 mpg since new with a very light foot and driving the speed limit.
 
Wheeewww . I am finally breathing a little easier. The first thousand miles I couldn't get this truck to get more than 15 mpg. The last tank 900 to 1200 miles it bumped up to 16.6 average. and that includes pulling a 35 foot trailer last weekend. FCA must have built in a fail safe to keep the truck in 8 cylinder mode until all eight pistons and cylinders are broken in? I'm seeing my ECO light on a lot more now.
 
Buying tier1 gas will have a better impact. I see a 2mpg difference between good gas and ****ty gas.
 
RAMBS said:
Wheeewww . I am finally breathing a little easier. The first thousand miles I couldn't get this truck to get more than 15 mpg. The last tank 900 to 1200 miles it bumped up to 16.6 average. and that includes pulling a 35 foot trailer last weekend. FCA must have built in a fail safe to keep the truck in 8 cylinder mode until all eight pistons and cylinders are broken in? I'm seeing my ECO light on a lot more now.
Click to expand...

That's a very interesting theory. I wonder if that could be confirmed any way?
 
I can't confirm what the mileage difference is, but my 3:92 Limited is awful on gas. I have the 33 gallon tank and it goes thru that in a heartbeat. I drive pretty reserved and have 2,000 miles on it currently. City is 12 MPG average and highway is maybe 15 MPG if there's no hills to climb and I have a tailwind. Now, did I buy a heavy V8 truck with gas mileage being my priority?...no sir. In saying that, I still feel its awful MPG for a vehicle built in 2018. My 2011 Jeep Grand Cherokee with the 5.7 Hemi has about the same range with its 22 gallon tank FYI.
 
superbird77 said:
I can't confirm what the mileage difference is, but my 3:92 Limited is awful on gas. I have the 33 gallon tank and it goes thru that in a heartbeat. I drive pretty reserved and have 2,000 miles on it currently. City is 12 MPG average and highway is maybe 15 MPG if there's no hills to climb and I have a tailwind. Now, did I buy a heavy V8 truck with gas mileage being my priority?...no sir. In saying that, I still feel its awful MPG for a vehicle built in 2018. My 2011 Jeep Grand Cherokee with the 5.7 Hemi has about the same range with its 22 gallon tank FYI.
Click to expand...

There has got to be another variable somewhere. I think my rig is heavier than yours with the ORP and I get a solid 17 MPG with 80-90 suburban driving. I saw a dip with the Pedal Commander since I couldn't not punch it, but I'm just over 1400 miles and it's been fairly consistent.
Someone mentioned the possibility of the rear end low fluid recall possibly causing this but maybe also front end alignment? Our build dates are so close that they should have the same software updates.

Have you tried different gas? I run 89 from Shell.
 
superbird77 said:
I can't confirm what the mileage difference is, but my 3:92 Limited is awful on gas. I have the 33 gallon tank and it goes thru that in a heartbeat. I drive pretty reserved and have 2,000 miles on it currently. City is 12 MPG average and highway is maybe 15 MPG if there's no hills to climb and I have a tailwind. Now, did I buy a heavy V8 truck with gas mileage being my priority?...no sir. In saying that, I still feel its awful MPG for a vehicle built in 2018. My 2011 Jeep Grand Cherokee with the 5.7 Hemi has about the same range with its 22 gallon tank FYI.
Click to expand...
Interesting. I averaged 18.4 on 2.25 hour roadtrip with cruise set on 70, with lots of hills. Got worse on the way bag into a 22 mph wind the whole way back, but still got over 16. I also have the 3.92 Limited.
 
Edwards said:
There has got to be another variable somewhere. I think my rig is heavier than yours with the ORP and I get a solid 17 MPG with 80-90 suburban driving. I saw a dip with the Pedal Commander since I couldn't not punch it, but I'm just over 1400 miles and it's been fairly consistent.
Someone mentioned the possibility of the rear end low fluid recall possibly causing this but maybe also front end alignment? Our build dates are so close that they should have the same software updates.

Have you tried different gas? I run 89 from Shell.
Click to expand...
I'm going to call the dealer and ask that question , I made sure to state in my 1st time in on recall fix that gas milesage is fkn HORRIBLE ... I'm curiouse to see if something like that oil in rear end coupd cause such bad numbers
 
Edwards said:
There has got to be another variable somewhere. I think my rig is heavier than yours with the ORP and I get a solid 17 MPG with 80-90 suburban driving. I saw a dip with the Pedal Commander since I couldn't not punch it, but I'm just over 1400 miles and it's been fairly consistent.
Someone mentioned the possibility of the rear end low fluid recall possibly causing this but maybe also front end alignment? Our build dates are so close that they should have the same software updates.

Have you tried different gas? I run 89 from Shell.
Click to expand...

I kinda thought the same thing as well. I have run 89 octane in it since I picked it up so I don't think that's the issue. Regarding the rear end, I don't know if there is recall data available to know if mine needs to be fixed. I currently get nowhere near 17 in city driving, I barely get that in the highway, lol.
 
Mr.Gigglez said:
I'm going to call the dealer and ask that question , I made sure to state in my 1st time in on recall fix that gas milesage is fkn HORRIBLE ... I'm curiouse to see if something like that oil in rear end coupd cause such bad numbers
Click to expand...

Let me know what you find out. My dealer is not very good at returning calls or customer service.
 
alacombe said:
I have the 3.92 and my MPG is crap and I dont even tow. I am currently averaging 12.9 mpg
Click to expand...
I’ve learned to drive like a “ old man” to work and back .(44 miles) I’m getting 20-21. If I turn up the HK audio system and drive like a Jr in high school I get 12.9 with the 3.92 gears. It’s all about you . Hard tho with that Hemi not to have some fun. Gotta pay to play.
 
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