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OK I have just read another post that someone on this forum is getting 20+mpg in their 5.9 Cummins. Can we all be truthful with each other? Please. I CALCULATED mine at 14.5mpg (the lie-o-meter showed 18-19ave) the other week. I am severely disappointed but with 10 years of owning the truck I have never seen better than 17. I have a freshly rebuilt trans and Tcase, 25K on injectors, bigger intercooler, cold air intake and many other new parts, brakes, U joints, and other parts that reduce friction. I just think people speak out of their :bart: or are :beer: when it comes to mpg discussions. If I am wrong please correct me and I will make adjustments to my truck to get the 20+mpg. Oh and I drive it very conservatively.
 

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Actually, LOTS of 5.9s get very good mpg. I ALWAYS figure the actual cuz I want to know the real thing. Your 5.9 does more like my 6.7... I rarely see 15. I had a 97 5spd 3.54 and a 03 6spd 4.10 concurrently for 9 months and I switched off commuting and towing to check the difference. On a 63 mile work commute, at ~60 mph. both got 21.0 consistently, before ULSD. ULSD cut them down to ~19.5. My 03 was my DD for 9 years and it got down to 18.3 in the summer, with AC always on in Az. and up to 19.8 in the winter. Craig
 

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A pic is worth a thousand words (also all documented on how I got there...)



Your bigger CAC & CAI are not helping.

11 yr makeover thread

https://www.cumminsforum.com/forum/3rd-gen-non-powertrain/2376698-11-years-345k-clock-time-makeover.html

Aluminum Driveshaft

https://www.cumminsforum.com/forum/3rd-gen-powertrain/2468821-aluminum-driveshafts.html

Lightweight pulleys

https://www.cumminsforum.com/forum/3rd-gen-powertrain/2508749-lightweight-pulleys.html


Electric water pump install
https://www.cumminsforum.com/forum/3rd-gen-powertrain/2512127-electric-water-pump-swap.html

other misc stuff
https://www.cumminsforum.com/forum/3rd-gen-powertrain/2520251-mpg-mod-info-consolidating-info-into-one-spot.html


Most recently took a mpg hit... was getting 22.8 @ the end of 2019, just found out why. 1 table tweek in HPT tune cost me approx 1~1.2 mpg





If you want it, there's a ton of info right there that tells you how to get it.


I have a spreadsheet with all the data for 2019 in it, average over the last 30~35k miles is 21.0x mpg... Cant wait to see how this summer goes, I expect 23's regularly with my typical routes. (nothing is flat here)
 

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OK I have just read another post that someone on this forum is getting 20+mpg in their 5.9 Cummins. Can we all be truthful with each other? Please. I CALCULATED mine at 14.5mpg (the lie-o-meter showed 18-19ave) the other week. I am severely disappointed but with 10 years of owning the truck I have never seen better than 17. I have a freshly rebuilt trans and Tcase, 25K on injectors, bigger intercooler, cold air intake and many other new parts, brakes, U joints, and other parts that reduce friction. I just think people speak out of their :bart: or are :beer: when it comes to mpg discussions. If I am wrong please correct me and I will make adjustments to my truck to get the 20+mpg. Oh and I drive it very conservatively.
So right off the bat, the CAI, bigger CAC are hurting, you want intake temps up as close to 100* with CTs up at 200*. Difficult to get there with the CAC being a bigger heat sink than stock, robbing temps out of the intake to the head. And to add, your stick with a 24~25*f differential from the airbox temp to the IAT temps, fan kicks on at that differential

Reduce rotational mass... less mass to get moving = less fuel used on every acceleration event. That applies to the wheels, tires, driveshaft, pulleys and if really motivated, ditching the water pump. It all adds up, combine it with custom tuning by you to leverage all of the changes and you'll see the benefit.

Reduce rail pressure at & below the cruise line for all rpms, that is a pretty good one right there. If your hauling a load, your not using it anyways but its there when the load is light or empty. Every rotation of the motor, think about the fuel being sprayed @ the rail pressure and duration. Higher rpms = more fuel used for the same rail pressure/duration combo.
 

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Steve, do you keep your fillups around the same gallons on purpose? Or just purely coincidence? I would figure that even if you went through tanks more, that the MPG would stay consistent yes?
 

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When tuning I fill up sunday night and friday after work... the mileage just works out that its around 300~350. Tank wise its around half a tank (remember I have the vent mod so all fillups are to the neck). When its a DGAS (dont give a sh!*) tank, I fillup whenever. That far right receipt in Feb 2020 was a dgas tank and still got over 21...

To be open, I had expected those tanks to start climbing up past 22... I made a change in the tune and forgot all about it. That change increased allowable fuel in certain parts of the tune, which unless I just happened to look at the rail pressure gauge, would never see it.

Oh, and with all the changes in the past couple of months to the tune, it is no where near dialed back in... I have been dropping RP, adding timing each go-around. The goal was to keep it close until I find the threshold where drive-ability suffers. With all that rotational mass gone & rail pressure dropped as far as I took it, it still is well within the limits for me. If I took the time to go get the timing dialed back in, mpg would jump again. ON the whoops I mentioned earlier, I just found that yesterday so I expect mpg will go back up into the 22's if not 23's with weather getting warmer.

Gotta love the cummins!
 

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Steve has put in a tremendous amount of time, energy and work into his mileage posts. There are a number of us who have stepped up and offered real and true mileage figures. I consistently get between 20.0 and 21.5 and have gotten 22.6 once. That is a stock engine, stock turbo, stock injectors and the only thing I've done is a Smarty SO6 straight #7 tune.

I applaud Steve for all the effort he's put forth to accurately log fuel mileage.

OP, if all you're getting is 15, something is up.
 

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liska, I agree, there are still plenty of FOSers (full of sht ers) out there, but there are so many variables, 20+ is not out of the ordinary, nor is 15, unfortunately.
I drive like I'm in a rental and fuel is free (sometimes), drive slow other times (not often, lol), pull a trailer, let it idle, don't let it idle. 8-21mpg is about my range, haha.

Note, only seen 21 like once, was driving county roads and back roads very conservatively for a couple weeks in the midwest flat lands, summer time, small tires, 55-60 mph tops, etc. And I managed to get 9mpg towing a 3klb cargo trailer once (90mph and head winds will do that). Everything else is in between!
 

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There’s quite a few folks on here who are either very elaborately lying on their Fuelly app and maintenance threads or they’re actually doing much better than your average owner. Me, I’m tickled pink to get 15.5 out of my 189k-mi 9200-lb 4wd mega dually in combined driving - and I don’t drive gently. Not exactly a lead foot but there’s no egg under my accelerator either and I’m not afraid of the big half of the throttle if the trans will hold it. Mileage is by and large down to the driver paying attention to what the truck is doing. Remember these are industrial engines. They like to be at a fixed rpm, IAT, and load. Keeping it there as much as possible increases efficiency. Varying is what mucks up the works.


Sent from my iPhone using Tapatalk
 

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Rpm will make a difference too. Our old '89 W250 5spd routinely got 20-23 except one time in TX on I 20 when I ran it at 80+ mph and in excess of 2300 rpm. That time it got 18 mpg. It would consistently get 16 mpg at 11k lbs with a camper on at 70 mph on interstates and 1-2 mpg less towing a Samurai or Tracker. That was over a 23 year span and 200k+ miles.

Now we have a '96 2500 5spd 4wd that has only been getting 17, disappointing. I'm hoping I can figure out a way to get better, hubs, OD of some kind, ??? It seems to run a bit more rpm than the old truck at 70 mph, probably tires. Both have 3.54 diffs.

Steve
 

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I think a lot has to do with WHERE you live and drive at, mostly level lands and MPG's should be a lot higher than in places where your up and hill, down a hill and up a hill every few miles
I had a buddy with a 5.9, bragged about getting close to 30 mpg's
then I went with him a trip from Ne PA to TN, to go pick up a trailer with a few cows in it
and he was barely getting 14 mpg's, empty on way down and worse once a trailer was added to things on way back LOL

he kept telling me a brake must be hanging up on trailer or something , and was playing with his handheld tuner making changes left and right,
I found it funny, all that hype and when time came to prove it , well??
seems a lot few them mods he was so power of that got him all that extra power and mpg's, just didn;t work as he claimed or expected, as on many of them long hills to get up and over, he was getting passed by Big rigs and couldn't understand way!
HAHA!
owned truck since new and had tunes done several yrs before this trip, and well, seemed like a lot of wasted $$ to me and that seat of the pants rewards came up empty!
 

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Sounds like op has a 600 truck. My 2003 6 speed did 21 once going from Phoenix to the Grand Canyon. Most of the time it would do 19 driving anyway you wanted.
 

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I get 18-20 on the freeway's and 14-15 in town or dirt roads, about 11 towing my home built gypsy trailer. 06 leveled with 315-70-17 tires. Auto transmission and 100% stock drive train. The truck does have free spin hubs but that didn't make a consistant observable difference, any one that says free spin hubs make a difference is full of beans!
 

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I will throw this out there, again (its been a year or so now), anyone doubting (and in the Seattle area) and wants to go for a road trip for a day and see for themselves, is more than welcome... Just expect to get peer pressured into some track time at the 2 kart tracks down in Portland :)
 

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I will throw this out there, again (its been a year or so now), anyone doubting (and in the Seattle area) and wants to go for a road trip for a day and see for themselves, is more than welcome... Just expect to get peer pressured into some track time at the 2 kart tracks down in Portland :)
Well you know I live in the Seattle area. I also can't lie about my mpg. And also believe you on yours:) also karts sound fun as hell.

Truck gets 15-19. All dependent.
I bought a TDI for for mileage.

Truck gets plenty of smiles per gallon for me
 

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I have been working very hard in a deliberate and reasoned way to make my truk the vehicle I want it to be. I have rigorously doccumented all of the changes I have made and looked at their impact as scientifically as I can.

I would call it a secret, but it has already been addressed here. The biggest factor is SPEED! I typically sit at 3psi of boost driving at 60mph +/- 3 mph. Or 1500-1600RPM. I spend 90% of my millage on the 25 north and south commuting 180 miles a day for work. My truck spends the bulk of its time operating at steady state with me just crusing along fat dumb and happy as people pass me. THIS is the single biggest factor in my having a tank give me 26mpg.

There are also some physical factors as well. I have a RWD truck with an auto transmission. I presently have 315/75R17 tires on the rear 3.73 axle. (I’ll be swapping in a 3.42 rear axle soon, and yes, I totally agonized over getting the speedometer right) I put in a cab to bed seal. I have been using a CAC blanket. And I drive like Miss Daisy wanted to be driven.


I have been following closely what Steve05Ram has been doing and learned a lot from his experiences.

I'm still figuring out using Torq for logging. (Had been using Blue Driver) and my overhead "Lie 'O Meter" is actually pretty close, even though it's still getting over the Titan tank install. The Distance to empty is woefully pessimistic.
 

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I think a lot has to do with WHERE you live and drive at, mostly level lands and MPG's should be a lot higher than in places where your up and hill, down a hill and up a hill every few miles
Yep, I've seen some people mention driving 55-60mph on the highways and such. Which sure will get you better mileage.

You do that here and you literally have a death wish. With most every highway having 65-70mph speedlimits but a few, and the normal flow of traffic (not even kidding) of any highway being 70 in the slow lane to 85-90mph in the fast lane, you literally are trying to cause a pileup driving 55mph.

I only drive into the office once in a blue moon anymore, but when I did it 4 times a week for 4 years or so, I drove in the fast lane doing 90mph the whole 26 miles on the highway and was in the flow of traffic.

I really feel bad for the guys driving semi trucks with limiters because everyone gets mad at them lol...
 

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Well you know I live in the Seattle area. I also can't lie about my mpg. And also believe you on yours:) also karts sound fun as hell.

Truck gets 15-19. All dependent.
I bought a TDI for for mileage.

Truck gets plenty of smiles per gallon for me
Sykart by Southcenter is the best in the local area... when things get back to normal, anytime... I'm in. Down in Portland, Syakart again and Pats acres... (50ish mph karts).

Since your familiar with the area... the commute is across the Tacoma Narrows bridge up I5 to the Renton area... only flat spot on that trip is past the Tacoma port... If I had to support a 2nd car, it would probably be a hi HP modern muscle car...
 

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Well you know I live in the Seattle area. I also can't lie about my mpg. And also believe you on yours<img src="http://www.cumminsforum.com/forum/images/smilies/smile.gif" border="0" alt="" title="Smile" class="inlineimg" /> also karts sound fun as hell.

Truck gets 15-19. All dependent.
I bought a TDI for for mileage.

Truck gets plenty of smiles per gallon for me
Sykart by Southcenter is the best in the local area... when things get back to normal, anytime... I'm in. Down in Portland, Syakart again and Pats acres... (50ish mph karts).

Since your familiar with the area... the commute is across the Tacoma Narrows bridge up I5 to the Renton area... only flat spot on that trip is past the Tacoma port... If I had to support a 2nd car, it would probably be a hi HP modern muscle car...
Yeah I've raced at the Skycart in Southerner a couple of times, work isn't too far from there.

Ah we have semi similar commutes. Yup, Fife on the flat spot. I drive from Lakewood to Kent every day, hence getting the TDI. Just had the pleasure of crossing Narrows last weekend going dirtbiking in the Belfair area. Felt good to ride some Moto again
 

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Yeah I've raced at the Skycart in Southerner a couple of times, work isn't too far from there.

Ah we have semi similar commutes. Yup, Fife on the flat spot. I drive from Lakewood to Kent every day, hence getting the TDI. Just had the pleasure of crossing Narrows last weekend going dirtbiking in the Belfair area. Felt good to ride some Moto again
Nice! you'd probably have fun @ Pats... Pats Acres - Racing Complex they resurfaced the track which brought with it some speed and lower times. At sykart in Tukwila, I was going quite a bit at lunch for 2-4 races but have scaled that back some. The new track layout is... eh.

I have yet to go to the ORV park out in Belfair, I do run across a lot of dirt bikes on the trail though out at Green Mtn while hiking.
 
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