MPG effect of 3.92 rear end

[Bearwhiz]

That, my friend, is the God's honest truth when it comes to pickup trucks.

I had a 2018 Ram with 3.21 and traded it in on a 2019 Ram with the 3.92. Big difference in how it pulls my boat.

 

[Gen3CoupeTX]

Mine seems to be getting better, climbed to 18+ now. I've not reset my MPG numbers during the first 2K miles. About 600 of these miles were Houston <> Dallas, the rest are in town; but not much stop-and-go city driving. Manual calculation shows 18 flat, but I've not had many opportunities with the 33 gallon tank. I do like this Hemi / 3.92 combo.

 

[sergetexan]

gen3 coup Texas - wow that’s a good number, R u 2 WD? I have the 2100 miles in Houston but only seeing 14.1 mpg hand calculated. I think my problem is the stop and go , very short trips and idling in traffic where this thing sucks up the gas.
The eco light comes on a lot now hopefully I can reach 15-16 and I will call it good.

 

[sergetexan]

Mine seems to be getting better, climbed to 18+ now. I've not reset my MPG numbers during the first 2K miles. About 600 of these miles were Houston <> Dallas, the rest are in town; but not much stop-and-go city driving. Manual calculation shows 18 flat, but I've not had many opportunities with the 33 gallon tank. I do like this Hemi / 3.92 combo.

View attachment 24250

 

[Gen3CoupeTX]

Serge, mine is 2WD. I'm rarely in Houston traffic as I work from home. My commute is most often to Hobby airport, and the typical errands in the 'burbs. I don't baby the truck, but I'm not romping on it either. Just driving ...

 

[EGD]

With 1640mi on odometer, I filled up and hand calculated at 15.16mpg, mixed and probably a bit of idle time since I had that steering issue and truck was at dealer for 2 weeks. The dash was showing 17.6, an optimistic 2.44 miles more than actual.

 

[barr0208]

just filled my truck up yesterday hand calculated went cruising downtown some highway. 17.9 mpg

 

[EGD]

Saga continues. truck a bit over 2000miles. The first pic is getting into Tampa. The second pic is just before hand calcualting the fill-up. It was 20.01MPG The offset between the DIC and hc has fallen to roughly 1mpg. The trip was primarily 95%H and 5% city. I used cruise control pegged at 70 with tach a tick under 2000rpm.

 

[Cr250Ram]

If you run the RPM number difference, the 3.92 causes the engine to make 20% more rotations over the 3.21 at 65 mph. **IF** that correlates to fuel use, then you should expect a 20% reduction in MPG at 65. However the 3.92 make the engine work less so less fuel is needed, especially in heavy load situations like towing and accelerating. So overall usage difference is likely less than 20%. If you are putting bigger tires on, towing a lot, or doing mostly city/traffic driving, I would say 3.92 if you have the choice. I saved $5,000 going to the exact same truck but it had 3.21s instead of the 3.92s I was about to buy. I couldn’t justify the cost at the end of the day. With that said if the trucks cost within 2/3k of each other I would have gone 3.92.

 

[SirLavidor]

A lot of good information here. Speed makes a difference because of drag. They say that after 60 MPH the drag exponentially increases. That said, my 4x4 with 3.92 gears doesn't vary much between 70 to 75 MPH with cruise control on fairly flat highway. I get about 18.5 MPG at either speed. On my Jeep it was about 3 MPG difference. I dropped down to 65 MPH and the MPG inched closer to 19 but not enough to be worth being a traffic hazard. Oh, I also have air suspension which lowers the truck at highway speeds. Around town I get about 15 MPG, which is still better than my Wrangler's 14 MPG mixed.

As for the Eco mode, my truck will kick in Eco at 70 MPH or lower on a flat highway. The slightest incline will deactivate Eco.

I knew to go with the 3.92 gears because my Wrangler came with 3.73 gears and I had to change them out to 5.11 gears, which oddly upped the MPG by 1. That taught me that the manufacturers like to use way high gearing for some reason unknown to me.

Oh, just one more thing, I use premium or mid grade fuel, which here in California is 89 and 91 octane. I read somewhere where they found it actually makes a difference in MPG but I do it because I don't drive much and the gas will sit for most of a month in the tank. I usually commute on my motorcycle.

 

[EGJ16]

I knew when I got the 2019 I was going to be lifting it and going with 34-35” tires. That was the main reason why I got the 3.92s. Second reason is for the “legal” towing capacity.

I drive a 2015 1500 with 3.21s at work and it cant move out of its way fast enough for my liking. It just didnt have that get up and go I was expecting from a hemi. I traded in a 2012 Ram 2500 with the 6.7 and when in the right rpm range, it pulled like hell with no signs of slowing down. It was my daily driver for 6 years so whatever I got had to at least be a bit nimble. While I usually try to go the speed limit, I also dont mind flooring it to go around a vehicle or passing vehicles. The 3.92s are perfect for me because while I can still get 17-18 cruising on the highway at 65, it will move when I floor it (Ive gone to 85-90 a couple times tring to pass a vehicle. Talk about a heavy foot lol). Im currently averaging 16.5 mpg with 60% highway (avg 60-65 speed limit)/40% city stop and go traffic. The only complaint I have it so far is that Im at 2k rpms at 65-70. Im going to level it and put 275/65r20s soon to help lower that and that should yield me some mpgs in return if I stay off the gas pedal. Like a couple of people have said, my eco light will come on if I let off just a tad bit when going a set speed. I can get it to come on at any speed with a bit of throttle manipulation. I have a 55 mile round trip to work with 50 being all freeway so Ive gone 60, 65, 70, and 75 for prolonged distances and I have kept the eco light on for the most part. Im still trying to figure out that sweet spot for my truck. But so far with my current tank, Im looking at getting 17mpgs. Which for the type of driving I do, I’ll take that all day. I just have 4k miles so we will see if it goes up anymore.

I will say, yesterday I drove a coworkers 2019 yukon with 3.08s and that thing couldn’t get out of its way if it wanted to. You could feel the weight of the vehicle when you drove it, not to mention it rode very stiff compared to my 2019. I floored it a couple of times and it wouldnt go anywhere. My truck on the other hand doesnt feel like how much it weighs, but neither did my 7800lb 2500 lol. After we drove the yukon, we hoped in my truck and I floored it a couple times to show him the difference and he just laughed and was in awe of how slow the yukon moved. Granted it wasnt apples to apples, it didnt feel like we were in a 5000lb truck.

 

[CNRETIREE2020]

My first tank was 12.5 MPG. I'm at about 4,000 miles now and I'm seeing and average of about 16.8 in mixed driving. It should get better; but it will never be great. I think that considering we have a truck with a V8, 4x4, and 3.92 gears that weighs close to 6,000 pounds; anything above 15 is not too bad. My old 2003 RAM 1500 ST Regular Cab, 4x4, 4.7 averaged 10 MPG and on a good day might have gotten 12 MPG. That is why my other car is a 2018 Chevrolet Malibu 1.5T.......36 to 41 MPG all day everyday.

Curious what would be considered the break in period on 2019 ram 1500? Where the gas mpg would be more consistent ratio?

 

[Willwork4truck]

Curious what would be considered the break in period on 2019 ram 1500? Where the gas mpg would be more consistent ratio?

Posters have said anywhere from 3K to 6K from what I recall. I have 6K on mine and frankly haven't noticed more than 1 mpg change, and if anything, it seems that highway has decreased by 1. I started off (3.21) getting 21-22 highway, was hoping for 23+. Now its 20-21. Course average speeds are all over the map, some stop n go, some 75-80. No real consistency when on I-40 near a major city...

 

[Billy James]

Curious what would be considered the break in period on 2019 ram 1500? Where the gas mpg would be more consistent ratio?

My MPG was horrible until I hit around 6,000 miles. I think break in, plus a couple oil changes has helped it to improve. My mileage has been pretty consistent since around 6,000; maybe even gotten a little better.

 

[Neurobit]

Just did a round trip to Houston-Dallas last week, and managed 19.4 (see my Fuelly sig).
This was on one tank of 89 gas (33 gal), and 70 MPH 90% of the way. I have 10k miles on my truck, and 3.21 diff. At that speed, my RPM shows to be around 1,600.

Used Adaptive CC the whole trip.

Cheers,

 

[Solosnavy]

I took a nice little road trip to the Pac 12 championship this weekend. started from So Cal and worked my way up to San Jose with stops in Monterrey and shopping. full round trip Millage 855.1 from driveway back to driveway including stop and go driving when i had to drive thru LA to get home. Truck is larame 4x4, 3.92, crew cab

 

[PMCurtis]

I just went on my first long drive, 420 miles to the coast and back. The trip computer said I was getting 16.2 Miles per gallon. When I did the math with the 30.2 gallons I fueled up with I get 13.9 miles per gallon. I currently have 1668 miles on the truck.

There is a big difference for 16.2 as stated by the truck vs. 13.9 doing the math.

It just goes to show that the trip computer is not the way to look at your mileage consumption. the simple math will be a better indicator.

 

[Billy James]

I just went on my first long drive, 420 miles to the coast and back. The trip computer said I was getting 16.2 Miles per gallon. When I did the math with the 30.2 gallons I fueled up with I get 13.9 miles per gallon. I currently have 1668 miles on the truck.

There is a big difference for 16.2 as stated by the truck vs. 13.9 doing the math.

It just goes to show that the trip computer is not the way to look at your mileage consumption. the simple math will be a better indicator.

Because of my Shell Rewards, I get 20 gallons every time that I fill up. I find the variance from the "Average Computer MPG" to the "hand calculated" to only be off by 0.2 to 0.4 MPG; with hand calculated even coming in at less sometimes. I'm pretty much at 16.5 for everyday stop and go traffic and around 18.0 to 19.6 on highway depending on my speed. I hand calculated for almost a year and then stopped because I didn't see much difference.

 

[Kooch80]

Decent in my opinion

 

[NDanecker]

been trying to convince many the lie o meter is not right. some closer than others but it's just a gauge or guess at what mpg you are getting. helps to learn driving style not a accurate number. hand calc is the only way.