Engine for fuel economy- 4.7 or 5.7?

teh603 · Dec 3, 2022

Doing some research here and elsewhere, and it looks like the 5.7 might, paradoxically, be the best on fuel economy. Power- to- weight ratios and all that. Is that true for the 3rd Gen, though? Or is that mainly true for the newest ones?

Currently driving a Libby and I'd like to at least get comparable fuel economy if I can (currently averaging a bit over 16 MPG if the center display thingey is any indication).

dhay13 · Dec 3, 2022

I had a 2007 1500 QC 4.7 with 3.92s that I bought brand new. Over 34,000 miles of hand calculating mileage my average was 14.207 MPG. Traded that for a 2013 1500 QC 5.7 with 3.55's and over 60,400 miles of hand calculating I averaged 15.524 MPG. Sure the 2013 was a little newer but still over 1 MPG better with the 5.7 and the 4.7 had the better gear ratio.

3pedals · Dec 4, 2022

Everything I’ve seen shows the 5.7 gets considerably better mileage than the smaller v8. My 2008 4.7 4wd 6spd has the lowest epa rated mpg of any factory vehicle that year (12 city, 16 hwy). It’s been a great motor/truck, but surely would’ve gone with a Hemi if it were available with a manual trans

I’m probably averaging right around 13mpg on a 4.7, and with over 400k miles on my truck that means it’s burned thru more than 30k gallons of unleaded

Daw14 · Dec 4, 2022

I’ve had both the 4.7 got around 13 mpg at best ,while my 2014 5.7 with 456 rear gear is at 18 to 20 if I drive easy. But it is pretty flat where I live , if that makes any difference.

zrock · Dec 4, 2022

not enough of a difference to really worry about.. when i got mine i looked at the specs for both and went with the 5.7

Rayzaa · Dec 4, 2022

You wont average 16 with a 3rd gen. I have a 3rd gen and thats close to my highway average. Been as high as 17.5 (No MDS) if i dont drive normally which means a little slower. But normally its around 16.5 on the highway. Average i dont know. All i know is its less.

I have a freind who always said, if you cant afford the gas, you cant afford the truck. Always made me laugh but what is the diff between the 4.7 and 5.7 mileage? If its only like 2 MPG, the 5.7 is a no brainer to me. Id rather have the power. Ive never had a 4.7 engine though.

teh603 · Dec 4, 2022

Rayzaa said:
I have a freind who always said, if you cant afford the gas, you cant afford the truck.

Yeah, I get the theory of that, but if I don't have the truck then I'll never get a camper. Can't even pull one home with a Honda Fit (the other vehicle, not getting replaced), and the local rental places charge $150 a day for a 1500.

And yes, I get that most people say to buy the camper first, then a tow vehicle to match. These are people who already have a tow vehicle to begin with, and my Jeep isn't really safe for towing any weight.

Dean2 · Dec 4, 2022

Have the 5.7 in a 2020 Grand Cherokee. It gets better, mileage in town and on the highway than the two of the same year with the 6 cylinder. It also has WAY better get up and go. The 2022 6.4 Hemi in a 2500 gets better average mileage than the guys are talking about for their 4.7s.

dhay13 · Dec 4, 2022

What year 4.7 are we talking about and how big of a camper? Up until 2007 the 4.7 was only about 230HP but in 2008 they added 8 more spark plugs (and I'm sure other stuff) and boosted that to something like 345 HP. I towed a 14x7 enclosed tandem axle trailer that weighed about 4000lbs loaded and on a trip from Pittsburgh to Indianapolis I averaged about 7 MPG and turned over 3000 RPM the whole way. Think it was closer to 4000 RPM. My 5 speed auto stayed in 3rd gear the whole way there and back because it didn't have enough power for the wind resistance. And that was with 3.92's

HemiLonestar · Dec 5, 2022

teh603 said:
Yeah, I get the theory of that, but if I don't have the truck then I'll never get a camper. Can't even pull one home with a Honda Fit (the other vehicle, not getting replaced), and the local rental places charge $150 a day for a 1500.

And yes, I get that most people say to buy the camper first, then a tow vehicle to match. These are people who already have a tow vehicle to begin with, and my Jeep isn't really safe for towing any weight.

How big a camper? The 3.7 KJ with 4x4 & towing package can tow 3500 lbs.

teh603 · Dec 5, 2022

dhay13 said:
What year 4.7 are we talking about and how big of a camper? Up until 2007 the 4.7 was only about 230HP but in 2008 they added 8 more spark plugs (and I'm sure other stuff) and boosted that to something like 345 HP. I towed a 14x7 enclosed tandem axle trailer that weighed about 4000lbs loaded and on a trip from Pittsburgh to Indianapolis I averaged about 7 MPG and turned over 3000 RPM the whole way. Think it was closer to 4000 RPM. My 5 speed auto stayed in 3rd gear the whole way there and back because it didn't have enough power for the wind resistance. And that was with 3.92's

Was that towing incident with an early 4.7 or a later one?

Either way, if the 2008 and later 4.7 is that much better, it's really good to know.

HemiLonestar said:
How big a camper? The 3.7 KJ with 4x4 & towing package can tow 3500 lbs.

Depends on who you ask. My wife, a small to medium hardshell or airstream. Me, a medium to large popup (or a small airstream with lots of windows).

The big issue with the Libby is the extreme amount of repairs it needs. Both diffs are worn out, and the engine both leaks and burns oil. Passenger airbag doesn't work (amber light stays on even with someone in the passenger seat plus the red dash light is out), a/c top hose is blown, and the radio is dead. The cost of getting all that fixed is more than the price of a 1500 in better condition.

TBH, my old truck (an '06 Colorado) had just gotten smashed, and I needed something quick and wasn't really in a position to finance like I am now. I expected to have to drop a fair bit on repairs, but... not quite as much as it still needs. So I'm looking to just cut my losses and move on.

dhay13 · Dec 5, 2022

teh603 said:
Was that towing incident with an early 4.7 or a later one?

Either way, if the 2008 and later 4.7 is that much better, it's really good to know.

Depends on who you ask. My wife, a small to medium hardshell or airstream. Me, a medium to large popup (or a small airstream with lots of windows).

The big issue with the Libby is the extreme amount of repairs it needs. Both diffs are worn out, and the engine both leaks and burns oil. Passenger airbag doesn't work (amber light stays on even with someone in the passenger seat plus the red dash light is out), a/c top hose is blown, and the radio is dead. The cost of getting all that fixed is more than the price of a 1500 in better condition.

TBH, my old truck (an '06 Colorado) had just gotten smashed, and I needed something quick and wasn't really in a position to finance like I am now. I expected to have to drop a fair bit on repairs, but... not quite as much as it still needs. So I'm looking to just cut my losses and move on.

'Towing incident'? The trip to Indy was with the 2007 4.7. truck was pretty new and only had about 10,000 miles on it at the time, probably less than 5000 actually. This was with the older style 4.7 that was about 235 HP. With the 3.92s it was fine in town or slower speeds but just lacked the power to get that trailer through the wind. The trailer was also a brand new 14x7 Haulmark tandem axle trailer.

teh603 · Dec 6, 2022

dhay13 said:
'Towing incident'? The trip to Indy was with the 2007 4.7. truck was pretty new and only had about 10,000 miles on it at the time, probably less than 5000 actually. This was with the older style 4.7 that was about 235 HP. With the 3.92s it was fine in town or slower speeds but just lacked the power to get that trailer through the wind. The trailer was also a brand new 14x7 Haulmark tandem axle trailer.

TBH, I wasn't sure what else to call it.

The "later" Rams I'm seeing with the 4.7, all claim to have around 310+ HP. That should make up the difference?

HemiLonestar · Dec 6, 2022

teh603 said:
Depends on who you ask. My wife, a small to medium hardshell or airstream. Me, a medium to large popup (or a small airstream with lots of windows).

The big issue with the Libby is the extreme amount of repairs it needs. Both diffs are worn out, and the engine both leaks and burns oil. Passenger airbag doesn't work (amber light stays on even with someone in the passenger seat plus the red dash light is out), a/c top hose is blown, and the radio is dead. The cost of getting all that fixed is more than the price of a 1500 in better condition.

TBH, my old truck (an '06 Colorado) had just gotten smashed, and I needed something quick and wasn't really in a position to finance like I am now. I expected to have to drop a fair bit on repairs, but... not quite as much as it still needs. So I'm looking to just cut my losses and move on.

Left out the fact that Libby was dying lol.

teh603 said:
TBH, I wasn't sure what else to call it.

The "later" Rams I'm seeing with the 4.7, all claim to have around 310+ HP. That should make up the difference?

2008 to 2013 Rams had the 310 hp version. Then it was replaced by a 305 hp V6.

CorDog009 · Dec 8, 2022

I stay around 15-15.5 with the 5.7 4wd and 3.92’s. I try to just do the speed limit or draft off of an 18 wheeler if I have to go very far. But these days I rarely even drive it, my car gets 25-27 most of the time. Actually I went to start the truck earlier and the battery is dead from just sitting around.

Ole Buck · Dec 9, 2022

04 with a 4.7 with everything but forced induction, 4.56 gears and rolling on 37's. 12.5 mpg all day long !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! thats just two mpg's less than the factory sticker said when she was brand spanking new.

Dean2 · Dec 9, 2022

Ole Buck said:
04 with a 4.7 with everything but forced induction, 4.56 gears and rolling on 37's. 12.5 mpg all day long !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! thats just two mpg's less than the factory sticker said when she was brand spanking new.

Happy for you but my V10 does very close to that and I have way more towing capabilty and get up and go. Small motors and bad gas mileage doesn't seem like a beneficial solution. It is like guys that drive tiny 4 banger roller skates to get 2 or 3 mpg better than I get in my V8 Lexus 430 GS.

dhay13 · Dec 9, 2022

Ole Buck said:
04 with a 4.7 with everything but forced induction, 4.56 gears and rolling on 37's. 12.5 mpg all day long !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! thats just two mpg's less than the factory sticker said when she was brand spanking new.

Did you re-calibrate your speedometer for the tires and gears? If not then that may not be accurate

HemiLonestar · Dec 10, 2022

Tire diameter is the only thing that affects pinion factor that year.

Ole Buck · Dec 10, 2022

Dean2 said:
Happy for you but my V10 does very close to that and I have way more towing capabilty and get up and go. Small motors and bad gas mileage doesn't seem like a beneficial solution. It is like guys that drive tiny 4 banger roller skates to get 2 or 3 mpg better than I get in my V8 Lexus 430 GS.

I don't drive big ass trucks and worry about gas milage. If I am worried MPG's then I am not enjoying myself or the work that I put into my sled. Had a tire kicker at the Shell station the other day look at me and say man i would hate to put gas in that thing and i politely said to him, believe or not i pay the same per gallon as you do. He just stood there. At the end of the day If it cost me a few dollars more then so be it. I enjoy the freedom of my truck. I went on a trip one time with a good friend of mine and his parents. His dad carried a calculator, note pad and pen and wrote down miles, gallons, time and all kinds of stuff. He double gripped the wheel all the way and I honestly don't think that he even enjoyed his trip because he was so worried about milage.

Engine for fuel economy- 4.7 or 5.7?

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