How can i get more fuel economy? I'm at my wits' end!

[jeffshafer]

Totally stock- get about 18. 5-19. 5 all aound- also pull 2times a week roughly 3800#s each time- 60 miles round trip- mpg is hand calculated



Jeff

 

[JBonpua]

I just posted on the "NO engine/transmission discussions" the following:



After following this board for a while before I ever bought my truck, I’ve read the horrible gas mileage on 3rd G56 equipped trucks getting less than 16mpg, I was shocked when I checked mine (all hand calculated). When I first took delivery of the truck it got about 17. 5 at about @ 300 mile on the clock. At 1. 5k miles it got 18. 32. At about 2k miles I installed a Banks Monster muffler and got 19. 27. At a little over 5k miles I installed an S&B filter kit and was getting 19. 61. All driving is 90% highway 20% city. No mod on the truck that can possibly affect MPG except for the Banks muffler, S&B filter and Leer cap. From what I’ve read on this board and from the little piece of card that was hanging on the cigarette lighter when I picked up my truck, MPG will improve once the truck reach 10k miles…can’t wait.



I also try to do what I can to increase my MPG by coasting to stop signs/red lights and launching gently from 2nd and keeping my RPM under 2k on the highway. I know at 2k RPM I am only going about 63 MPH but I’m not always in a hurry so no big deal. If I need to be somewhere at a certain time, I just start my trip 5-10 minutes earlier.



My hope is to break 21 MPG when I reach 10k miles when I replace the engine, transmission & differential with Amsoil. I am also thinking about putting those Airtabs on top and sides of my cap. What do you all think?

 

[CRandal]

i too only got 13 city 16 highway. until my transfer pump died. warranty fixed it but i was told that the new one had to be installed in the fuel tank. I gained 3 miles a gallon there. at the same time i installed a k and n cold air intake and got another 2 mpg. My best mileage has been high 23's. tomorrow i get my 4 inch exhaust.

 

[JHenry]

I don't think anyone is reading what I originally wrote as far as mods. I think I should get better than a stock truck with 13k miles on it and 7,000 foot altitude! I am at 5 feet above sealevel, 25 feet max! I just think that I should get what my old man gets in his 04 with a 6 speed, stock, but same truck, he is getting 22 mpg 30 % city, 70 % hwy driving and keeps it at 60 mph and has stock size tires, running empty. I'm thinking of repowering with a 4bta! Twin turbo!

I have always heard that automatics will get worse mileage than manual. I have an '06 2500 crew cab with 39k on it. I have a Banks Technicooler with Ram Air Intake, Banks straight through muffler, AFE Stage II filter, silencer ring gone, Jacobs exhaust brake, 24" tires on 19. 5" wheels, and Dyna-Trac hubs. I just returned from a trip through some mountainous regions in lower British Columbia. Average was about 21 mpg for the whole trip, at 60 to 70 mph. The Dyna-Trac hubs actually contributed the most with a 1 1/2 to 3 mpg increase after installation. JH

 

[mr.wilson]

Spending money to save money???

Sure there are a few basic things you can do: LOTS of good clean air in and LOTS of air flow moving away from the turbo. Everything else will cost you more money. At what point does it pay off 10K miles 100K miles, that depends on how much you are willing to spend. Synthethic oil front to back, good exhaust (1200CFM) and K&N intake netted me about 3 mpg. I feel pretty good pushing a 7K brick down the highway averaging 17 MPG. I added a BD valve body and picked up almost another . 5. My next step will be to add a better Torque converter. I have also read that a cam swap can net you an added 1 to 2 mpg if you are willing to spend the 3 or 4 thousand dollars. I don't know about you but I can buy a lot of fuel for four-thousand dollars. Not to throw a monkey wrench into your search but be happy.

 

[rbattelle]

That way, the mixture is very rich in the injection zone, and zero away from it. Fuel can burn much more completely, since there is an abundance of oxygen. Hence the superior fuel efficiency of diesels at low power levels (in addition to the lack of pumping losses across the throttle plate, and the higher compression ratio, and higher BTU of fuel).

I disagree. In my opinion, diesel fuel has a lower BTU content than any of the spark ignition fuels.



The reason for the better fuel economy is compression ratio. As we know, efficiency is a heavy function of compression ratio: higher compression equals higher efficiency. In fact, I believe if you were able to run a spark cycle at the same compression ratio as a diesel cycle, the spark engine would be more efficient.



Spark ignitions have a much lower knock-limited MEP, so you can't approach the efficiency of a diesel. Direct injection gasoline technology is an attempt to help close the gap a bit.



As for stoichiometric fuel air ratios, there is a limit to the relative fuel air ratio you can run in a diesel (F/Fstoich). As you approach 1 (and move beyond), there's not enough time for all the fuel droplets to vaporize and combust. As a result, you get smoke - and lots of it.



Note also that above a relative fuel air ratio of about 0. 87, you're not getting any significant improvement in MEP... you're just making noise and smoke.



Regarding the debate over cool, dense air in a diesel, the I see the tradeoffs as such: denser air is good, cooler air is bad. Denser air affords more opportunity for combustion. Cooler air inhibits the vaporization of fuel droplets (which is the primary factor in diesel combustion in my opinion). In fact, it's been shown that warmer inlet air improves ignition delay.



There is a such thing as air that is "too cold" (as evidenced by increased smoke production in cold weather), but no such thing as air that is "too dense".



Anyway, those are my thoughts. Take 'em for what they're worth.



Ryan

 

[brods]

I disagree. In my opinion, diesel fuel has a lower BTU content than any of the spark ignition fuels.



... ... .

Tisk tisk. That is an easy one to check on. Minimum number I've seen for #2 is 130,000 BTU while the best gas numbers are around 126,000 BTU. No doubt diesel has more heat content per gallon.



As for the rest, read the link betterthanstock gave it has a lot of good info, scroll down: http://www.cummins.com/au/pages/en/p.../faq/index.cfm



Here is an interesting gasser explanation: http://mb-soft.com/public2/engine.html

 

[rbattelle]

Tisk tisk. That is an easy one to check on. Minimum number I've seen for #2 is 130,000 BTU while the best gas numbers are around 126,000 BTU. No doubt diesel has more heat content per gallon.

My source indicates the following lower heating values:

#2 diesel fuel (C13H28 @ 0. 920 specific gravity): 18000 Btu/lbm
Gasoline (C8H17 @ 0. 702 specific gravity): 19020 Btu/lbm

On a volumetric basis, the higher density of diesel fuel means it has more energy content. On a mass basis, diesel has less energy. In my opinion, the mass basis is more descriptive.

It's just my personal preference to deal in mass rather than volume. Mass never changes, whereas volume does. It makes more sense (it's simpler) to me to deal with mass.

[Note: specific gravity = density/density of water]

Here's a thread that got into it a few years back.

Ryan

 

[brods]

LOL... . ok. But remember fuel mileage is measured in miles per gallon. When we start saying moles per mile... ...

 

[rbattelle]

LOL... . ok. But remember fuel mileage is measured in miles per gallon. When we start saying moles per mile... ...

Good point. Not only that, but we purchase fuel by volume rather than mass. So the volumetric energy content really is the more significant in terms of economics.



Ryan

 

[DHerbeck]

Thought it was time to chime in with my experience:



2006 QC Laramie, 2WD, Auto, 3. 73, stock tires, stock everything. I will say things got better after 10,000 miles. I am an honest person, not bragging here, telling the straight truth. I drive the same 250 mile stretch of road, north/south. I hand calculate every tank. I will say that on the highway, I hand calculate about 2-4 MPG better than the overhead, but in town and towing, it is pretty close.



My best MPG driving from S to N was 24. 6, that is 65 MPH, cruise, slowing down to 45 several times through small towns. There was about a 10-15 MPH tailwind. The next week I made the same exact trip and thought of this..... when I am only putting 11 gallons in, does it make a difference if I fill up right off the road when the fuel in the tank is hot, or when it cools overnight? So the next week I did the same run, filled up the next day and got 24. 4, so the conclusion to me was that the temp of the remaining 24ish gallons did not change its volume.



Wind resistance and speed make all the difference in the world. I have made this same 250 mile run from Tulsa to Dallas probably 15 times in the past 6 months. I have driven all of it at 55, 60, 65, 70 and 75 where legal. I never speed. I notice a decrease of 2 MPG for every 5 MPH I increase in speed.



I routinely get 22 MPG at 65 MPH 1800 RPM, 20 MPG at 70 MPH 1950 RPM, 18 MPG at 75 MPH 2100 RPM. I tried 55 MPH, it was hot, and at 1500 RPM, I was spinning the fan through the viscous clutch, got 18MPG! Way too much drag spinning the fan. I am thinking an electric fan might help.



I have a 20' enclosed car hauler, v-nose, 2500 LBS empty. This surprised me... . I pulled it to Minneapolis, 700 mile run empty, got 13. 5. Put a 2500 pound car in it, drug it home, got 13 MPG. That tells me wind resistance is far worse than weight to these trucks, as many of you have said already. Wind resistsnce increases with speed and that can be seen in our MPG figures as we speed up.



I just emailed with AAM and have a part number for 3. 42 gears. I found a local shop that has ordered them for me from AAM. I am starting another post on this subject. Please come debate with me, watch me smile, or cry as I spend about 600 bucks chasing a 2 MPG increase!!



One more thing, RUN YOUR AIR CONDITIONING all you want, it hurts me NONE!



Dave

 

[Cattletrkr]

There is a such thing as air that is "too cold" (as evidenced by increased smoke production in cold weather), but no such thing as air that is "too dense".

My '01 would only smoke in the summer and the '04. 5 smokes more in the summer. Kinda hard to tell shades of black with the '04. 5 though... :-laf

Everyone I ask, their truck is the same way. More smoke and better mileage in the summer.

Not saying this proves anything, just sayin'.

 

[BBowers]

Hey Cerberusiam! Too bad oxygen is not a catalyst, it is a reactant! Read your Chem book! What goes on in a diesel or gas engine is an oxidation-reduction reaction! Platinum/palladium catylasts in the cat converter are catalysts, because a catalyst is not consumed in a reaction. A catalyst by definition assists in a reaction without being consumed/reacted itself. Oxygen is definitely consumed ina diesel otherwise we woulnt make co2, co, and nox as well as water!

 

[AKaiser]

One more thing, RUN YOUR AIR CONDITIONING all you want, it hurts me NONE!



Dave

Best thing you can do to improve your fuel economy, is to roll up the windows and turn on the AC (if you need AC). The power needed to run with the windows rolled down more than offsets the power gain from not running your AC, depending on the speed you're driving and how much you drop the window.

 

[TMConroy]

I'm with you in pain. I'm getting 12. 2 hwy and only 10. 8 city. Pure stock with no changes yet. Mileage is at 9000. I brought it to the dealer twice and he said "all the numbers look good" He even took it for a test drive (40 miles) and got the same mpg as I've been testing for the last three months.



This really sucks. Looking at lemon laws in CA but the sticker didn't have a mileage rating. Any suggestions for this diesel novice is greatly appreciated.



Oh, one more thing. When I bought it, the LCD mpg read: 15. 9. Never have I seen it again.



Help!!!



06 Dodge 3500 Laramie 5. 9L 2x4 LWB 3. 73 LSD

 

[bmoeller]

I hope you don't drive like a granny all the time

Too much easy driving and it will lose MPG from not getting enough "exercise. " Crank that Bullydog up, put some weight in the back (or hook on a trailer), and give it a nice long run at 75+ MPH

Yep. I do better after blowing the cobwebs out, too. :-laf:-laf Need to pull a trailer once in a while to get the engine good and warmed up. Replacing the brake calipers and RH ball joints helped, too. They were dragging. Mileage is coming back up some.

 

[BHolm]

I chime in and share my experiences. I am on my fifth third gen, all diesel 4x4 autos, all 3. 73 gears plus the one Hemis truck that gets 15-16 mpg doing the same type of driving as the diesels do, just no trailer pulling.



My '03 QC SB would get 23mpg on the highway, it would get 15 hauling my car to the drags at 70-75 mph, best milage I ever got with one of these trucks, never should have sold it. My '03 dually reg cab would only get 15-16 doing the same driving, worst of the bunch. The '05 QC LB would get 17-18 in mixed driving but I sold it at 36k so I suspect there was some improvement left I never realized. My well broken in 46k mile Mega gets 20 mpg in mixed driving. When new it was around 13-14 mpg. Several cross country trips pulling heavy trailers helped immensly. It has run 28-30 lbs of boost for 10-12 hrs a day for what equates to several weeks. That I believe is the difference between the trucks getting good numbers and those not, though it doesn't explain the duallys poor milage.



All of mine have been stock, except 285 tires on the srw trucks. I think bigger tires, lifts and power adders all bring milage down. I am tickled with the 20 mpg on my 7700 lb Mega. I also think that for highway milage the autos are superior with slightly taller gearing than the manuals. Lock up convertors make them just as efficient as the manuals, and the lower rpm adds economy.



I am now considering a G56 3. 73 truck. I will follow the 3. 42 thread with great interest as I think that is exactly what the manual trucks need.

 

[SAndreasen]

i get 15 to high 17 somtimes 18 but rarley this includes driving in town short trips few minutes idle up few minutes idle down . hauled cows to sale and average 80mph at 21k got ten mpg. can usualy get around 12. 5 pullin. i dont know but i cant realy expect more out of a truck that weighs 7800 pounds and puts 300hp and 619 ft. lb torque to the rear wheels. my cousins gas can barley match my towing numbers when hes empty

i also hate any temp above 65 and run the ac nite and day

 

[Regcabguy]

Tall thins.

Without a doubt a truck equipped with the stock tires will achieve the best fuel mileage. However,take them into some soft stuff and the truck sinks like a rock. I wish the tire manufacturers would produce a tall thin one with perhaps the following specifications: Lt 275-80-17(or 16),load range "E". It would fill the wheel wells,minimize air resistance,and allow airing down in the event of a stuck situation. The footprint upon airing down would be elongated vs. widened as in a typical oversized tire. It would certainly fill the bill on my g-56 equipped '07. In light of the recent fuel price increases,maybe some real world tests could be justified by the tire guys. Wishful thinking.

 

[SAndreasen]

i have 285 75r 16 3. 54 gears i run 2050 rpm at 80mph