Worse mileage towing with 6.4 2500, than 5.7 1500?

[Millnoff]

So towing on the same roads, trailer, conditions, and speeds, I'm getting 3-4 mpg worse in my 14 2500 with a 6.4, than my 11 with 5.7?

Is this a normal thing? Kinda disappointed to be honest, not that I was expecting better but didn't expect worse.

 

[monteholic]

a 2500 weighs considerably more than a 1500, it also has a larger engine, gear ratios are different

you seriously expected to get at least the same?

 

[Millnoff]

Yes, I was i guess. 2500 is about 1500lbs heavier than a half ton isn't It? I towed almost 9k with my half ton and still got better mileage than I'm getting pulling about 6k with my 3/4 ton...

5.7, 5 speed, with 3.55s
Vs
6.4, 6 speed, with 3.73

Just expected better I guess

 

[Docpaulo]

Not happening... bigger engine.. higher gear ratio... heavier truck

 

[RoadRamblerNJ]

Rule of thumb, 2500s w/ 6.4 avg 11-12 mpg. Really doesn't matter much if you hammer it or baby it. They also sit considerably higher than a 1500, having the aerodynamics of a bigger brick.

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[McBroom]

Millnoff are both trucks 4x4? If not that alone will make a big difference...


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[smurfs_of_war]

I had this same surprise when I switched to a 2500 6.4, but then I remembered:

1. Aerodynamics- the 1500 is a brick. The 2500 is an apartment building.

2. Everything about the 2500 is heavier. Even the parts that need to rotate. With not much more HP and TQ, the 6.4 has to drink a bit more to do this.

3. It takes a LOT of muscle to move this weight.

4. The 1500s are designed with the best possible fuel economy in mind. The 2500s are designed to be beaten like a mule.

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[CostaRam]

Higher, bigger and heavier pay it's tribute to fuel consumption and there is the point where a diesel's low-end torque kicks in.
Chris

 

[Ratket]

The Cummins gets amazing mpg when you compare it to a 6.4.

 

[mtofell]

WOW! Some crazy opinions and "fake news" on this thread. The body of a 1500 and 2500 are the same thing. One sits slightly higher. There is no "brick" and "building". They are the same thing aerodynamically speaking. I'll gladly concede the 2500 is much heavier which will impact MPGs.

This is just flat out incorrect - "rule of thumb 11-12 MPG no matter how you drive it." Reality is far from it. I have 65K on my 6.4 Hemi with a wide variety of towing and daily driving. I've owned 4 different 1/2 ton and 3/4 ton trucks over the last 20 years and BY FAR my 6.4 Hemi has the most variable MPGs depending on driving and usage (towing or not, etc.). I can easily get 20 rolling at 55 with no wind. Sitting in traffic stop and go I'm lucky to crack 10. I'd love to see some proof from this "rule of thumb" you speak of because I've never read anything like it in 4+ years of hanging out here.

And finally, OP - 3-4 MPGs difference towing? Really? Give us some hand calculated numbers and terrain specifics because until then I'm calling BS. Daily driving I'd buy it but towing? Nope.

I get that this is the internet and we all fudge a bit to make a point but come on guys.... there's some serious BS being thrown here.

 

[Rampant]

Not happening... bigger engine.. higher gear ratio... heavier truck

Ummm... the 3.73 in the 2500 is a LOWER gear ratio than the 3.55 in the 1500.

 

[Dmopar74]

Actually the hood and grill are bout 2" taller, and the front bumper is larger. Both willlead to reduced aerodynamics. Not alot but every little bit helps, or hurts in this situation

 

[smurfs_of_war]

WOW! Some crazy opinions and "fake news" on this thread. The body of a 1500 and 2500 are the same thing. One sits slightly higher. There is no "brick" and "building". They are the same thing aerodynamically speaking. I'll gladly concede the 2500 is much heavier which will impact MPGs.

This is just flat out incorrect - "rule of thumb 11-12 MPG no matter how you drive it." Reality is far from it. I have 65K on my 6.4 Hemi with a wide variety of towing and daily driving. I've owned 4 different 1/2 ton and 3/4 ton trucks over the last 20 years and BY FAR my 6.4 Hemi has the most variable MPGs depending on driving and usage (towing or not, etc.). I can easily get 20 rolling at 55 with no wind. Sitting in traffic stop and go I'm lucky to crack 10. I'd love to see some proof from this "rule of thumb" you speak of because I've never read anything like it in 4+ years of hanging out here.

And finally, OP - 3-4 MPGs difference towing? Really? Give us some hand calculated numbers and terrain specifics because until then I'm calling BS. Daily driving I'd buy it but towing? Nope.

I get that this is the internet and we all fudge a bit to make a point but come on guys.... there's some serious BS being thrown here.

My 2500 catches WAY more wind than my 1500. More frontal than on the side.

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[RoadRamblerNJ]

WOW! Some crazy opinions and "fake news" on this thread.

This is just flat out incorrect - "rule of thumb 11-12 MPG no matter how you drive it." Reality is far from it. I have 65K on my 6.4 Hemi with a wide variety of towing and daily driving. I've owned 4 different 1/2 ton and 3/4 ton trucks over the last 20 years and BY FAR my 6.4 Hemi has the most variable MPGs depending on driving and usage (towing or not, etc.). I can easily get 20 rolling at 55 with no wind. Sitting in traffic stop and go I'm lucky to crack 10. I'd love to see some proof from this "rule of thumb" you speak of because I've never read anything like it in 4+ years of hanging out here.

Flat out incorrect? Really? Tell you what. You call me out on 3 different days and I'll take a picture of my avg mpg for you. Guarantee you it will be 11 or 12 mpg. Not 10, not 13. OK? I drive almost 100 miles every day. About every 3 days, I put roughly 24 to 26 gal. of regular in. I'd be happy to photocopy the receipts for you for, say, 3 weeks. I beat the **** out of this truck and get 11. I baby it and get 12. Only towing experience was a 400 mile run to VA. with a full bed and a full 6x12 Uhaul enclosed brick. I ran at 80 all the way and got 10.2 mpg. Brought it home empty, same speed, got 11.5. Since you've only been driving 1/2 and 3/4 trucks for about half as long as I have, maybe you should pay attention more. I have no reason to be here other than to possibly help out some youger fellas, not to argue with the likes of you.



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[Docpaulo]

Ummm... the 3.73 in the 2500 is a LOWER gear ratio than the 3.55 in the 1500.

You're right... my bad... but lower gear makes for worse mileage...

 

[Rampant]

You're right... my bad... but lower gear makes for worse mileage...

Yes, it does make for worse mileage... that's why what you said didn't make sense. No biggie. It happens to the best of us.

 

[68PowerWagon]

Ummm... the 3.73 in the 2500 is a LOWER gear ratio than the 3.55 in the 1500.

Maybe not.. 6 speed vs. 8 speed... what is the final drive gear ratio on the 8 speed?

 

[RoadRamblerNJ]

Maybe not.. 6 speed vs. 8 speed... what is the final drive gear ratio on the 8 speed?

Excellent question! From what I could find,

1500 8th gear is 0.667:1
2500 6th gear is 0.625:1 so:

1500 = 0.667 X 3.55 = 2.367 final ratio.

2500 = 0.625 X 3.73 = 2.331 final ratio.

Difference is negligible and in no way causing the mileage loss seen by OP in my opinion.

Below are all the 8 spd ratios if anyone is curious

The ratios are (this is for all 1st gen 8HP transmissions to include the 8HP45, 845RFE, and 8HP70).

1st-4.714:1
2nd-3.143:1
3rd-2.106:1
4th-1.667:1
5th-1.285:1
6th-1.000:1
7th-0.839:1
8th-0.667:1
R-3.300:1

6th is the direct drive gear, so it has 2 overdrives. The 2nd gen 8HPs such as the 8HP75, which I strongly suspect will appear in the 5th gen Rams, have a wider range:

1st-5.000:1
2nd-3.200:1
3rd-2.143:1
4th-1.720:1
5th-1.314:1
6th-1.000:1
7th-0.822:1
8th-0.640:1
R-3.456:1

6th is still direct drive


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[Rampant]

To anyone who has ever towed anything over 5000 lbs or so with both a 1500 & 2500 knows that the final drive numbers don't matter in this case. The towing experience is night & day different. It's all in that the components in the 2500 being bigger, thicker, stronger, heavier, etc. That's everything in the suspension, brakes, driveline and the hitch itself. Everything is just beefier. Don't forget rotating mass... tires are bigger and heavier too.

Other than interior and sheetmetal, the trucks are completely different animals. My truck weighs 7110 lbs cleaned out with the gas light on. Most commonly-optioned 1500s probably don't weigh that much while maxed-out on payload. That is why the 3/4 ton gets worse gas mileage. Very simple.

 

[Mitag3]

At first I was a little surprised with your results but thinking about it, stepping up size in trucks with a gas motors seems to just gain you stability and towing prowess unless you dramatically change gearing. To gain towing stability and mileage you'd have to go diesel