This MPG is why I bought the 3.21

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ramffml

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Couldn't resist after seeing a bunch of negative posts on the 3.21. I get why this forum is so lopsided, it's an enthusiast forum so many will be drawn to the 3.92.

But this week I just crushed my best record to date (which was 2 years ago). Back then the best I got was 9.4 l/100 km = 25 mpg. This week, my truck displayed this little goody on the dash:

8.4 = 28 mpg

3 hours 100% freeway driving, avg of 103 km/h, with a light tail wind, MDS disabled, mix of 89 and 91 octane fuel, probably some ethanol in there but cant be certain of the amount.

Reset meter, hopped on the freeway, and snapped pic after 3 hours on the off ramp. So yes, all ideal conditions but it's still far better than anything I've seen with the 3.92. And I probably won't see that again ever, but there is no doubt the MPG savings of the 3.21 are real.

ram - 8.5.png
 

KoboldTaco

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I get why folks want to get good MPG right now considering the cost of fuel. I was happy to spend 6.33 two days ago when filling up since the last time I filled it was 7. But, and yes there is a big but here…a truck is not for the MPG-friendly mindsets. Just drive it. If you want good mpg, a Prius I sold was the trick. That monster got 61 mpg and I didn’t drive it like a *****. It just literally got that good of mileage After 60K miles, that was the average of those miles.

Yes gearing makes a slight difference but overall, I’ve yet to see a huge swing like the OP reported. I think that had more to do with the way it was driven at that moment. I’m happy to be proven wrong.
 
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ramffml

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I get why folks want to get good MPG right now considering the cost of fuel. I was happy to spend 6.33 two days ago when filling up since the last time I filled it was 7. But, and yes there is a big but here…a truck is not for the MPG-friendly mindsets. Just drive it. If you want good mpg, a Prius I sold was the trick. That monster got 61 mpg and I didn’t drive it like a *****. It just literally got that good of mileage After 60K miles, that was the average of those miles.

Yes gearing makes a slight difference but overall, I’ve yet to see a huge swing like the OP reported. I think that had more to do with the way it was driven at that moment. I’m happy to be proven wrong.

Think about my engine revving 400 to 500 rpms lower than yours, for 3 hours... sustained. Going the same distance, same speed, same tail wind, same fuel, yet you're revving 400+ rpms over mine. That's why the 3.21 is going to get me much better mpg.

It's like you can only think in terms of "prius" or "mac truck" and nothing in between. I bought my truck to pull my trailer. So I "need" the truck. Those times when I'm not pulling, I'm definitely concerned about MPG.
 

Zoe Saldana

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Couldn't resist after seeing a bunch of negative posts on the 3.21. I get why this forum is so lopsided, it's an enthusiast forum so many will be drawn to the 3.92.

But this week I just crushed my best record to date (which was 2 years ago). Back then the best I got was 9.4 l/100 km = 25 mpg. This week, my truck displayed this little goody on the dash:

8.4 = 28 mpg

3 hours 100% freeway driving, avg of 103 km/h, with a light tail wind, MDS disabled, mix of 89 and 91 octane fuel, probably some ethanol in there but cant be certain of the amount.

Reset meter, hopped on the freeway, and snapped pic after 3 hours on the off ramp. So yes, all ideal conditions but it's still far better than anything I've seen with the 3.92. And I probably won't see that again ever, but there is no doubt the MPG savings of the 3.21 are real.

View attachment 497724

Sorry to say - higher the computer MPG; the less accurate it is.
 
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ramffml

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Sorry to say - higher the computer MPG; the less accurate it is.

Not true at all. It's usually the other way around, as you drop in fuel efficiency a difference of "1 mpg" between computer and hand calc is more significant, because a 1 mpg means more when you only get 10 towing, vs a 1 mpg difference at 25.

1 mpg difference at 10 mpg = 10% difference
1 mpg difference at 25 mpg = 4% difference

Even if your statement is correct, it would effect both 3.21 and 3.92 equally and lets face it, we're not seeing very high 3.92 numbers.
 

crazykid1994

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Sorry to say - higher the computer MPG; the less accurate it is.
Idk if yours is that way but when I used to get 18-19mpg my computer said 19-20mpg. Now that I get 12-13mpg my computer will say anywhere from 13-15mpg. It’s almost always been 1-1.5mpg off when I had calculate.
 

KoboldTaco

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Think about my engine revving 400 to 500 rpms lower than yours, for 3 hours... sustained. Going the same distance, same speed, same tail wind, same fuel, yet you're revving 400+ rpms over mine. That's why the 3.21 is going to get me much better mpg.

It's like you can only think in terms of "prius" or "mac truck" and nothing in between. I bought my truck to pull my trailer. So I "need" the truck. Those times when I'm not pulling, I'm definitely concerned about MPG.
Why start a thread and not consider opposing views? The way I see it:

1) I offered my understanding by saying I understand why folks need/want better MPG.
2) Offered a perspective based on the thread you started.

I never intended to offend, but I do take your response as a defensive position and that's fine too. Let us continue to enjoy the community and the conversation without offense. :)

I’ll never get 28 MPG with a 3.21 rear end since the engine I run simply won’t produce that level of mileage. Indeed, unladen backhauling without towing you will want to maximize. Having worked in the distribution business I get that too.

The hard part is with our bricks in the wind, over a certain speed, the wind drag alone washes out the rear-end ratio but I don’t have hard data to reference so it is nothing more than my opinion. There was a thread earlier this week where a guy was going to pay a ton of money to switch out his rear end. Not sure where is break-even point was but a bunch of good data there regarding wind drag. Glad you are getting the MPGs that you are.

Thanks for reading and again, never intended offense. Take care.
 

HEMIMANN

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Best I got with my 2012 Ram 1500 & 5.7 Hemi was 20 mpg pure highway, mostly flat, on 89 octane, with 3.73 gears. EVIC readout - I didn't calculate by hand. I figured if they couldn't do a mileage algorithm by this point, the world is lost. I guess they can't. Bye, world!

I upgraded to 2500 with 6.4L, came with same gears. I would have preferred 4.10's, but it does ok with 3.73's and a tow tune. The 5.7 was untuned, I was still working then and too busy to mess around. It was just adequate for loads I towed. The 6.4 doesn't work as hard.

Edit: it also was 4x4, running in 2WD in summer.
 
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Jeepwalker

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Glad you are getting good MPG. What's your truck configuration (2or4 WD, which cab)? Why did you have your MDS turned off?

When I figure out my mpg, I generally hand calculate each tankful for about a month or 1.5 months. That's 'average' obviously. But in your example, it does illustrate that pretty good mpg numbers are achievable with such a large vehicle, at least straight down the HWY. Especially handy to know for someone planning a decent road trip or commuted long distances daily.
 
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ramffml

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Why start a thread and not consider opposing views? The way I see it:

1) I offered my understanding by saying I understand why folks need/want better MPG.
2) Offered a perspective based on the thread you started.

I never intended to offend, but I do take your response as a defensive position and that's fine too. Let us continue to enjoy the community and the conversation without offense. :)

I’ll never get 28 MPG with a 3.21 rear end since the engine I run simply won’t produce that level of mileage. Indeed, unladen backhauling without towing you will want to maximize. Having worked in the distribution business I get that too.

The hard part is with our bricks in the wind, over a certain speed, the wind drag alone washes out the rear-end ratio but I don’t have hard data to reference so it is nothing more than my opinion. There was a thread earlier this week where a guy was going to pay a ton of money to switch out his rear end. Not sure where is break-even point was but a bunch of good data there regarding wind drag. Glad you are getting the MPGs that you are.

Thanks for reading and again, never intended offense. Take care.

My bad, I'm not actually offended nor did I read your post that way. I tend to come across that way on the internet (I've stumbled across my own posts from months ago and thought "wow, that sounded harsh" :rolleyes:).

Anyway, I wasn't defensive, just showing that there are more than two sides to the argument. Your "argument" (and what I've seen posted here many times) is that trucks aren't supposed to care about mpg because it's not a prius. My response to that is, some of us "need" the truck for doing truck-y things sometimes, but still want to eek out the best mpg we can when it's just used to go from point A to point B. It's not silly or wrong to want this. It's wrong to expect 30 mpg, yes, but not wrong to aim for maximizing mpg as best we can (hence my gear choice).

Glad you are getting good MPG. What's your truck configuration (2or4 WD, which cab)? Why did you have your MDS turned off?

I have a relatively light "level 2" big horn. 4x4 CC. My payload is 1750 so that gives a bit of reference as to how light it is, most 5th gens are several hundred pounds less in payload.

I turn off MDS because I feel that it doesn't work. One of those ideas that work in theory but not in practice so much. My best results so far have all been with MDS disabled. My last record of 9.4 was also with MDS disabled.

MDS basically turns off half your engine and stresses the other half (basically 4 cylinders running WOT) but lugging while doing it (low rpms but high load = bad). It shakes sometimes in and out of MDS. I have no facts or data to support this, but I'm convinced it's better for the life of the engine to let it coast around easily with 8 cyliders firing, vs running 4 at pretty high load.
 

bdc2

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I got 16.6 hand calculated over 485 miles last week if I can trust google maps on the distance. The computer showed 15.9.
This was mostly at 67 uncorrected on 285/18 mud tires.6.4 6speed 4.10 2500. That truck usually gets under 14. I guess every dog has its day so to speak
 

EdGs

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The evic on my 2015 1500 SLT QC 5.7L 8SPD 2WD 3.21 w/146k miles usually hovers around 19.5 in my normal daily life, IF I watch my use of the skinny pedal....lol.

My truck is bone stock, and I don't disable the MDS either. Also, no throttle controller, though I am interested in the 9drive.

When I am traveling in the SE between FL and NC, the evic has been as high as 23.7. Hand calc is usually about 1mpg less.

I have used 87 gas almost exclusively in the almost 120k miles since I've owned it. No towing, very little hauling also.

Very happy with the mileage, but less wouldn't be a dealbreaker as I wanted the hemi. If I wanted MPG, I would've got a small car.

That being said, I have wondered if the MDS has anything to do with the exhaust manifold bolt breakage, since it seems to me there would be heat differences due to cylinder deactivation.

But I wouldn't be surprised if I were wrong. Love my truck and would buy another in a hearbeat if the deal was right.
 

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Good news for truck ownners: I paid $4.14 for 87 octane this am. My brother paid $3.89 two days ago at a large grocery chain (that sells cash fuel cheap). Looks like the price is coming down.
 

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The evic on my 2015 1500 SLT QC 5.7L 8SPD 2WD 3.21 w/146k miles usually hovers around 19.5 in my normal daily life, IF I watch my use of the skinny pedal....lol.

My truck is bone stock, and I don't disable the MDS either. Also, no throttle controller, though I am interested in the 9drive.

When I am traveling in the SE between FL and NC, the evic has been as high as 23.7. Hand calc is usually about 1mpg less.

I have used 87 gas almost exclusively in the almost 120k miles since I've owned it. No towing, very little hauling also.

Very happy with the mileage, but less wouldn't be a dealbreaker as I wanted the hemi. If I wanted MPG, I would've got a small car.

That being said, I have wondered if the MDS has anything to do with the exhaust manifold bolt breakage, since it seems to me there would be heat differences due to cylinder deactivation.

But I wouldn't be surprised if I were wrong. Love my truck and would buy another in a hearbeat if the deal was right.

Wouldn't manifold bolt break on both sides? Maybe not, depending on the heat flux arrangement - don't know if both forward cylinders are the same type. The real gearheads on here will! (too lazy to look up). If they are opposites, it could explain why the one on the passenger side is always breaking.
 

EdGs

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Wouldn't manifold bolt break on both sides? Maybe not, depending on the heat flux arrangement - don't know if both forward cylinders are the same type. The real gearheads on here will! (too lazy to look up). If they are opposites, it could explain why the one on the passenger side is always breaking.
I did have 1 bolt broken on each side, the rearmost one. In the back of my mind, I dont think it is the mds, but combined with improperly heat seasoned manifolds, who knows?
 
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ramffml

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Wouldn't manifold bolt break on both sides? Maybe not, depending on the heat flux arrangement - don't know if both forward cylinders are the same type. The real gearheads on here will! (too lazy to look up). If they are opposites, it could explain why the one on the passenger side is always breaking.

The MDS cylinders are evenly split, left to right and front to back. Basically everyother cylinder in the firing order are turned off.

I have heard that theory before, makes a lot of sense to me that the uneven heat might cause warping.
 

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There's a theory floating around,that the trucks actual exhaust system,might be a bigger contributor to manifold bolt breakage,then we think.Example being the 5.7 cars use basically the same cast iron log manifold,but with a set of dual pipes,that lead back to an X farther towards the rear of the car,then the trucks squashed midpipe is,and the cars don't break manifold bolts. The theory does make you wonder if the actual exhaust system on the trucks might be putting more stress on the back manifold bolts,then we think,as it's always the back bolts that break,which is where the exhaust pipes would be exerting the most pressure.You'd think if it was totally heat related and temp changes breaking bolts,the front bolts and middle bolts would be more inclined to break,but i've never seen or heard of a truck actually breaking a front manifold bolt
 
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