MPG effect of 3.92 rear end

[Willwork4truck]

This thread could go on forever, as long as there are different driving styles, wants and needs there will be different opinions. Ram owners are fortunate in this respect at least, the engine choices are limited to a single one in each category. Just read a F150 thread about which 2015 or newer motor is the best and you will see more flaming and "stuck in concrete" ideas than Carter had pills. I read hundreds of posts denigrating or praising one engine vs the other. People just couldn't leave it alone.

 

[ScottW19]

I have the 3.92 on my Laramie Crew with the 33 gal tank. Mixed driving I am getting about 16.7 with 4500 miles. Live at sea level

 

[SilverSurfer15]

Lol the f150 forums are great! The ecoboost crowd is the worst... it’s like all the ricers from the 2000s got older and moved into THAT truck.

 

[mstanko]

I haven't found a concrete answer...or really any semi-firm answer even on this. I've read the 3.21 is a little "ho-hum" off the line, but the 3.92 would be significantly better. Does that rear end cause a noticeable drop in MPG, either city or highway?

Dealer told me about a 1 or 2 mpg. I am getting about 14 to 15 with mine with a 3.92

 

[Couchsachraga]

eTorque, ORG, and 3.92 makes for fairly lousy mileage it seems. 15.7 seems to be a longer term average, though when I headed on an extended trip (with canoes on the roof no less!) I managed to have a tank at 17mpg. I'm sure it will suffer more when put 34 or 35's on Like most of us though I didn't get a crew cab pickup for the mileage but for the capability. Very happy with my choice, my only MPG disappointment is normally I can do a bit better than the EPA rankings by driving conservatively when I feel like it, and with how RAM reported them there's no hope of that!

 

[Tac747]

I will agree that with my 3.92 gear Rams the ECO lamp was on a lot more than my '19 with the 3.21. Since my towing requirements are now down to a few thousand pounds, I don't need the 3.92 anymore.

Best regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Now at: 013355 miles.

Where is the ECO lamp. I have never seen one lit up on my dash

 

[Bigtone]

Where is the ECO lamp. I have never seen one lit up on my dash

You have to enable it at the uconnect. It's called "Fuel saver display in cluster", under the display settings.

 

[ForTehNguyen]

when the transmissions get more and more gears, the rear end gearing is much less of an issue as compared to the past when there was only 5-6 speeds

 

[SilverSurfer15]

Yes and no.

The number of gears has no effect on highway performance, as the O/D ratio is still roughly the same as its always been. So yes the extra gears get you going and such, but even with 15 gears you won’t be able to run 70 with 37s and 3.21s in final gear with a ratio of .68 or whatever.

 

[ExcursionDiesel]

I already commented on this thread ... But feel compelled to again. The 3.92 was a mandatory option for me. I've never once owned a vehicle and wished it had higher (lower numerically) gears. Okay, maybe back in the day when transmissions were 3 or 4 speed, and you needed to take your 4.11 or 4.56 hot rod on the interstate. I contend that with mixed use, the 3.92 isn't going to sacrifice MPG to the 3.21 ... And it would never be significant enough to make me question my choice. The little Eco light is on more than it's off. I don't use my truck for racing, as a supercharged Viper checks that block. Not street racing of course - Much too old to get busted for that!

Not my measured experience. Maybe my mixed use is different than yours. My 3.92 cost me 2-3 mpg on the highway and is about the same as a 3.21 in town. Yes, it feels quicker, tows better...but not without a little trade off. The is no free lunch.

 

[RedRocketZ28]

I was hoping for better MPG out of my truck but 3.92's were a must for me. I frequently tow a car trailer and a 26' boat. My last tow rig was a 2003 2500 Suburban with the 8.1L and 4.10's. It was a beast and I didn't want to take very many steps back when towing. My 2003 Silverado 1500HD with the 6.0L and 3.73's was such a complete turd while towing and it got 7-8 MPG towing our boat. The Suburban got 9-10 and would stay in OD unless pulling up a decent hill.

I've only towed with the Ram once so far and it was only about 4200 lbs. I locked out 8th gear and it still downshifted quite often on any type of hill. However, it towed very well and I expect it to do well with the boat too. Will it tow as well as the BBC Suburban? No.

Also, I drove a 3.21 truck and then a 3.92 truck. The 3.21 truck felt neutered to me.

 

[Dusty1948]

I was hoping for better MPG out of my truck but 3.92's were a must for me. I frequently tow a car trailer and a 26' boat. My last tow rig was a 2003 2500 Suburban with the 8.1L and 4.10's. It was a beast and I didn't want to take very many steps back when towing. My 2003 Silverado 1500HD with the 6.0L and 3.73's was such a complete turd while towing and it got 7-8 MPG towing our boat. The Suburban got 9-10 and would stay in OD unless pulling up a decent hill.

I've only towed with the Ram once so far and it was only about 4200 lbs. I locked out 8th gear and it still downshifted quite often on any type of hill. However, it towed very well and I expect it to do well with the boat too. Will it tow as well as the BBC Suburban? No.

Also, I drove a 3.21 truck and then a 3.92 truck. The 3.21 truck felt neutered to me.

I don't know why, but when I ordered my 2014 the 3.55 axle was available in Hemi equipped 1500s. That wasn't the case when i ordered the 2019, and as far as I know it still isn't available with the Hemi. The 3.55 might be a good compromise for everyday driving, but if I remember correctly it didn't increase the towing very much.

Best regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Now at: 013361 miles.

 

[Willwork4truck]

Couple comments then I will leave it be... Tac747 asked where the eco light was... well if you drive it like a hemi wants to be driven then maybe it hasn’t ever “needed” to come on, haha.
Red Rocket - my brother had a 2001 3500 with the 8.1 and 4.10’s, dually 2 wheel drive. That was a towing beast for sure.
I am a bit surprised the 6.0 didn’t do too well, a lot of van expediters have that engine and like it. They are sometimes close to maxed out payloads in their line of work and they really like it over the 4.8.
SilSurfer, definately true. Ever hear the 18 sp semis go through the gears? Just helps them stay in their torque band, being so narrow.
ScottW19, thats decent mileage for mixed conditions I think. My 3.21 is sitting at 18.0 and thats mixed but absolutely babied driving. Probably hasn’t cracked 3K rpm yet! Grandpa here...

 

[SpeedyV]

I was hoping for better MPG out of my truck but 3.92's were a must for me. I frequently tow a car trailer and a 26' boat. My last tow rig was a 2003 2500 Suburban with the 8.1L and 4.10's. It was a beast and I didn't want to take very many steps back when towing. My 2003 Silverado 1500HD with the 6.0L and 3.73's was such a complete turd while towing and it got 7-8 MPG towing our boat. The Suburban got 9-10 and would stay in OD unless pulling up a decent hill.

Also, I drove a 3.21 truck and then a 3.92 truck. The 3.21 truck felt neutered to me.

Wow...we’ve had unusually similar truck histories!

My last rig was a 2003 GMC Sierra 1500HD SLT Quadrasteer 4x4. I had 4.10s, though, as well as a custom Magnaflow exhaust and Black Bear tune, so it pulled like a beast. Payload was awesome on that “heavy half”...nearly 2,800 lb. On the downside, I averaged 11 mpg and maybe saw 14 once.

Before that, I had a 2001 Chevy Silverado 2500HD crew cab with the 8.1L / Allison combo. That truck was built to pull a house: 2WD, 4.10s, and a 45-gallon Transfer Flow fuel tank, and a dual chambered exhaust. That beast rarely downshifted, even under load. Ironically, my mileage wasn’t terrible for an engine with eight grapefruit-sized cylinders; I typically saw 9-11 mpg in town and up to 14 on the highway.

Like you, the 3.21s just didn’t work for me on the new Ram, especially when cross-shopping GM’s 6.2L and Ford’s 3.5L TT. I went with the 3.92s and eTorque to help compensate.

 

[Andress]

Im at 5,500k miles and Im getting 11.8-12.7mpg

Looks like thats as good as its gonna get lol

 

[Tac747]

Couple comments then I will leave it be... Tac747 asked where the eco light was... well if you drive it like a hemi wants to be driven then maybe it hasn’t ever “needed” to come on, haha.
Red Rocket - my brother had a 2001 3500 with the 8.1 and 4.10’s, dually 2 wheel drive. That was a towing beast for sure.
I am a bit surprised the 6.0 didn’t do too well, a lot of van expediters have that engine and like it. They are sometimes close to maxed out payloads in their line of work and they really like it over the 4.8.
SilSurfer, definately true. Ever hear the 18 sp semis go through the gears? Just helps them stay in their torque band, being so narrow.
ScottW19, thats decent mileage for mixed conditions I think. My 3.21 is sitting at 18.0 and thats mixed but absolutely babied driving. Probably hasn’t cracked 3K rpm yet! Grandpa here...

I agree but even when the cruise is set at 65 on flat level ground I have never seen the light come on. I just checked my settings and fuel saver mode in display is on so I guess I will never see it.

 

[SilverSurfer15]

mine doesn’t usually work in that zone either. It should come on in the 45-50 zone. And again in the 70+ area. At least this is how my truck behaves.

No idea why, just something I’ve noticed. Mine is most aggressive at like 30-50. It tries to come on at all times.

Also try it without the cruise, the cruise control is almost always under too much load because it doesn’t understand you can lose and gain speed.

 

[Joecameron69]

The website is great. As for the app, I have the paid version (3 or 4 $ or something). You can enter fueling data on your phone when you're at the pump and later download into an ASCII file for Microsoft Excel.

I did not even know they had a app, just downloaded it. thanks

 

[ExcursionDiesel]

Cruise Control keeps MDS (ECO Light) off most of the time because it is constantly adjusting the throttle. ECO won't engage until it sees a light load for around 1 second. Doubt me? Try this: drive 50 on flat ground then back off the throttle just a bit for a second...viola, ECO every time. Works at any speed. The problem is that at speeds over 65-70, the engine load is too high to maintain ECO without a slight downhill or tailwind.

 

[Electrical]

I did not even know they had a app, just downloaded it. thanks

Awesome. It was an acquisition a few years ago, the app existed and then Fuelly bought them. Hopefully whoever wrote the app saw a nice payday.