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Howdy, I am new here to this forum, so bear with me.. I have a couple of questions.
I’ve been looking at a few forums, but couldn’t seem to collect the right opinions I was looking for.
I currently have a 2008 Dodge Ram 1500 with a 5.7 Hemi, but potentially exploring the option of a 5.9L Cummins, somewhere in the 3rd generation. I would also consider a 6.7L Cummins early 4th Gen, but more so interested on the 3rd Gen 5.9. What has sparked in my curiosity is fuel efficiency, and if it would change from what I currently experience. I do some occasional towing (once a month) but no more than 4500lbs. Empty I will get around 13.4 MPG on a good day with the 5.7 Hemi. I was Wondering if the 5.9 Cummins would do better or worse, and what years are best to worse. Looking for your opinion, and more information on these trucks in general as I have never owned a Cummins. I am from Canada, if that helps. Thanks!
 

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The Cummins will do better in most instances.
The truck in my Sig is doing 18.6 mpg with mixed Hwy/in-town driving, unloaded.
With the weight, you are pulling you will beat the empty mpg of the Hemi.

Lots of info has been posted all you need to do is read it.
 
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Cummins will be better all around. My city/local MPG stays about 14.5. HWY I see 20 if cruising.
 

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FE has to account for the difference in energetic content of a gallon of fuel. Diesel is 1.3X gasoline.

Then, how is this represented in the price of fuel?

Gasoline average nationally was recently $2.85/gl. Diesel would need to be at $3.70/gl as equivalent. So long as it stays below the one-third threshold, diesel is something of a bargain. As above, it was at $3.13/gl.

Another way to see it is to take steady state highway MPG for the gasser and multiply it 1.3X. 14-MPG = 18.2-MPG.

$82 versus $56 at current prices gas vs diesel in this scenario.

Note that this is only a slice of ownership/operational expense. It’s probably reasonable that a gas truck engine could work to capacity up to 200k miles. What does a rebuilt cost? $5,000?

At 200k the diesel is yet short of the rebuild stage (operated carefully without stupid go-fast stuff), BUT will need new injectors and injector tubes, etc, plus labor to install. $3-5,000 isn’t outside of normal.

This also doesn’t account for the price differential new or used of buying a diesel. Do those comparisons.

If one is continually booking up to 14k loads, the diesel is wanted. Not really otherwise. Desire isn’t need. Won’t pay the freight.

All that said when driven extra carefully to minimize fuel burn to near lowest then 18-MPG is low. I only see numbers below 20 when towing. Truck spec, climate, topography and driver motivation all factor in.

A Diesel engine is expensive to buy and so is its maintenance/repair when that becomes necessary. Forloads too heavy for 1/2 and gas 1Ts, it’s king. For working past 200k without issue it’s great when one stays ahead of service intervals.

For a suburban toy that’s mainly a commuter, the door closed on diesel bring cheaper long-term after diesel prices became higher than gasoline AND emissions regulations became tighter circa 2008.

Gas motors of today are a far cry from the EFI’d 1960s motors that hung on until the early 2000s as turbodiesels became popular. Gasoline is simply easier to live with and cheaper to buy/own. Plenty of fleets that used to buy diesel pickups (oilfield, for example) went back to gasoline.

The numbers have to work. Length of ownership + odometer miles in that time have to make sense. And only when the load would more rapidly degrade a gas motor.

6, 8, & 10-speed autos keep the gas motors ON THE MONEY for torque. Live long, live strong. That’s the coup d’grace.
 

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If you are wanting to get another truck just for fuel efficiency, I'm not too sure that would make the most financial sense as the prices are through the roof at the moment. Back when you could pick up a decent truck for well under 10k it was fine.

Empty just cruising around I get in the low 20's average, with a 7500lb boat it's around 18ish. I've seen 25+ going on country roads at 45-50 miles an hour.

For the most fuel efficient cummins full size truck that would have to be the 2wd manual single cab 1st gen, it was easy to get 22mpg average without trying, but then they only have a fraction of the power out of the box.

If you don't need a truck all the time and want a efficient diesel then look into a VW tdi, mine gets 48+ on average and certain versions are just as reliable as a 12v cummins.
 

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My ‘04.5 cummins gets 16-17 mpg while towing 4-5k trailer and my 2010 hemi grand cherokee gets 13-15 mpg unloaded. I’ll take the Ram any day over the jeep, especially with current gas prices.
 

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A manual transmission will get better fuel milage for most comparisons. Keep that in mind too
 

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Also put into account the 4 speed and 6 speed autos. The extra gears help for fuel economy. I think the 5.9 is an all around better engine then the 6.7 due to emissions. BUT, if one was to have a deleted 6.7 with the bigger 6 speed...then by far you'll get more power and extra MPGs.

FYI - you could always throw a better transmission at any cummins. Especially the autos. They are the Achilles heel.

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IMHO, fuel economy is what the OP is asking.

Diesel is cheaper than gas in much of Canada.

The hemi does it's best in conditions that allow the MDS to function.
 

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Empty just cruising around I get in the low 20's average, with a 7500lb boat it's around 18ish. I
Just pointed out your typo on your 7500lbs towing mpg #s. We don’t want the OP do be terribly mislead and disappointed.
 
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It's pretty accurate for my house to the lake and back, most of it is going 50ish there are hills up and down, but a lot of the time can be spent in neutral.

I do have to say that with the way the manual trucks are geared from the factory one does not achieve the best milage going 80+ mph. An automatic is a much faster truck for the interstate highways. A locking hub also gives a slight boost, along with electric fans, not saying a bone stock truck will give the best fuel efficiency possible.

This guy is the deceiving one, I've never been able to achieve what it says.

928755
 

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@Random Waffle I have a 2008 6.7 Cummins, 311K miles and still on original transmission, and it has cost me very little to own with little to no breakdowns (fingers crossed) besides 2 water pumps and 2 alternators, front ball joints and u joints in 200k miles/7 years. It is deleted, and has a 2nd gen swap kit (different turbo and manifold than oem setup) with very good tuning that you probably can't obtain any longer sadly... 3.73 gear, 4 door, short bed, 4x4, not lifted, and every other little detail is listed in my signature.

But for my truck and where I live (Kansas 1,100ft elevation) my fuel mileage has a fairly decent fluctuation between the hot and cold temperatures I notice. Say generally in the winter with a good amount of idle time + mostly highway driving (75-85mph) I get avg of about 13-15mpg in the cold months. Now in the summer time, with the same idle time and road speeds as winter, I am getting about 17-20mpg. I don't always calculate every fill up, but those numbers were got by dividing miles by gallons a few times here and there, and NOT my overhead display.

I am running a +120HP tune, I don't tear stuff up, but I do drive a lot harder than the average asleep/zombie commuter, and I rarely tow anything. My A/C currently isn't operational either lol. But my summer and winter mpg estimates are with all the above already factored into that.

So you would more than likely achieve the same MPG, if not MORE than what I have I feel like, but I could be wrong. I personally think most any 3rd gen 2003-2007 5.9l will treat you VERY well if you find a good one, and I wouldn't be scared of the 6.7l as long as you can do things to it that are needed without law issues. Just keep in mind, that when things do break....they are generally more expensive as stated before. Anddd 3rd gen 5.9l Cummins are also going for more than the price of gold just incase you didn't know.

Just giving you a brief run down on my experience and opinion, but if it's within reach and you're interested, go for it.

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It's pretty accurate for my house to the lake and back, most of it is going 50ish there are hills up and down, but a lot of the time can be spent in neutral.

I do have to say that with the way the manual trucks are geared from the factory one does not achieve the best milage going 80+ mph. An automatic is a much faster truck for the interstate highways. A locking hub also gives a slight boost, along with electric fans, not saying a bone stock truck will give the best fuel efficiency possible.

This guy is the deceiving one, I've never been able to achieve what it says.

View attachment 928755
Ive seen 27 a number of tanks. Conditions account for most of it. Solo, under 1100-lbs in bed, etc. (Many more details)

I also know how to get it . . STARTED with truck spec before buying one.

Highway planning average (the low number) is 24-MPG. All conditions except mountains or towing.

One is willing to work for it or not. Same for achieving 350k before rebuild. It’s not automatic.
 

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It's pretty accurate for my house to the lake and back, most of it is going 50ish there are hills up and down, but a lot of the time can be spent in neutral.

I do have to say that with the way the manual trucks are geared from the factory one does not achieve the best milage going 80+ mph. An automatic is a much faster truck for the interstate highways. A locking hub also gives a slight boost, along with electric fans, not saying a bone stock truck will give the best fuel efficiency possible.

This guy is the deceiving one, I've never been able to achieve what it says.

View attachment 928755
We call it a Lie-O-Meter for a reason... only claim I'd buy is one that has fuel receipt with hand calc'd mpg number on it.

Edit: mine is actually now on the low side by about 0.5 mpg. It regularly tells me 22.8~23.0 and actual is 23.3~23.5
 

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Mine has never even been close to the MPG lie o meter either, but I don't drive it gently either.

This weekend will tell how much my tunes and mods have helped/hurt MPG. 37's aren't helping my situation, but I didn't buy it to baby it, I bought my truck to do what a diesel can do and it's awesome.

As others have said, if MPG is a big enough concern, then a manual is the way to go. Plus, you won't have to pony up for an eventual rebuild like you will with the auto. Not to say the manuals are perfect, but the stock 4 speed is most certainly a time bomb.
 

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Mine has never even been close to the MPG lie o meter either, but I don't drive it gently either.

This weekend will tell how much my tunes and mods have helped/hurt MPG. 37's aren't helping my situation, but I didn't buy it to baby it, I bought my truck to do what a diesel can do and it's awesome.

As others have said, if MPG is a big enough concern, then a manual is the way to go. Plus, you won't have to pony up for an eventual rebuild like you will with the auto. Not to say the manuals are perfect, but the stock 4 speed is most certainly a time bomb.
bed seals will help mpg regardless of trucks config... info in the aero thread.
 
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