Well I havent towed my RV yet, but went a good drive this weekend about 5 hours each way, most gentle hills here in the Iowa. Going to Omaha I drove with the cruise set at about 75 and got about 17.5 mpg hand figured. Coming back we drove a little slower at 65 mph and got about 21 hand figured.

This is unloaded with me wife and 2 little ones under the age of 3. This goes to show those that speed does play an important factor in mileage.

Now my truck is a 05 with 6k on it now and is stock.

Just a little FYI, you will be able to extend that hi-way mpg to 75 (or close) with a 285 tire.

I still can't figure out how people get such good fuel mileage.

I drove 240 highway miles this weekend.

Kept it between 72 and 74.

I got 15.5 mpg hand calculated.

Hmmm.....

I still can't figure out how people get such good fuel mileage.

I drove 240 highway miles this weekend.

Kept it between 72 and 74.

I got 15.5 mpg hand calculated.

Hmmm.....

I am with you on not being able to figure out the high mpg numbers. My 05 LLY get 14.5 to 14.8 at 72 mph, both on DIC and hand calculated.

Diesel fuel foams a lot when you fill a tank. On my truck I can put in another 10% after the pump clicks off. If you have a neck full tank, drive 200miles and pump in fuel until the pump clicks off you may have put in 10gals or 20 mpg. If you can put in another 10% or 1 gal more then you are at 18 mpg. The only way to know what your average mpg is to keep long term records. I have had as high as 22mpg and as low as 10mpg (Iowa winter 3miles to work and shut it off). My 20,000 mile average is 16.6 and my highway only average is 18.5. Some people only talk about their best tank and never their worst. Point your truck into a 40mph head wind some time and post your MPG.

While that is true I fill my tank everytime till I see fuel not foam in the fill nozzel. The stationI go to has a slow pump so less foaming while On the road I ised the high speed pumps and had to wait a bit for the foam to die down and fill to the top.

I avg about 17.5 on my weekly drive from marion IA to Iowa City for workabout 80 miles round trip about 10 miles city driving and the and 30 highway one way.

I am happy with the milage I am getting with this truck atm it is saving me about 40 to 50 dollars per week over my 03 6.0 gasser, same trip hadto fill the tank twice a week . that truck got at best 13 on the highway and never did check in town driving.

Well It Must Be Something About The Good Iowa Air That Helps The Milage.
I Get Up To 23 To 24 Mpg On Good Days.( 50 To 55 Mph ) At 65 To 75 That Drops To 17 To 18.5 AT 90 MPH IT COST$ 115.00 FOR THE Speeding Ticket On I 29..

Most Of My Driving Is Betweem Des Moines And Rathbun, Ia..

Arm

I haven't had my truck long, but I've been getting 23-24 mpg at about 70mph. Around town I'm getting about 17. I can actually go a week without filling the tank a couple of times!

I had an '03 lb7 and the "sweet spot" for mpg with that setup was 68 mph. Go above that and the mileage drops off fast - real fast. My best was 21.5 mpg driving from portland, oregon to sacramento, Ca - averaging 68 mph.

I haven't checked the highway only mileage on my '05 yet; Too busy at work and home to "get away"...

jeff

CW--Just out of curiosity, how much difference in time was there when you did one part of the trip at 75 mph and the return leg at 65? My experience has been that there usually is not too much time difference since there are generally many occassions when it's necessary to slow way down and advantage of any higher speed spurts is lost. Sort of a tortise and haire type of thing.

yet another mpg thread. How fun. Is anyone over 21 mpg actually hand calculating? Just curious.

Not only that, but they don't have their truck info in their sigs. So, you don't know what they're running. There's some difference in whether they're running stock tyres, camper shell, fuel conditioner, 2x4 vs. 4x4, etc. or not.

It makes it tough to compare bananas to bananas.

Yeah, what gruffid said. There is also a HUGE difference between standard cab short beds and crew cab long beds. We need to know specifics to have any real comparison. Personally, I cant get more than about 16.5 on the highway at 65 mph

First to aka108 I drove down on a Sunday Did't really time the drive but only stopped twice for bathroom breaks. came back on a Monday stopped twice for bathroom breaks and in Newton Iowa went thur a drivethur for Lunch.

To those that need the specs of my truck here they are

I own bought in June an 05 2500hd crewcab, only addon atm is nerfbars. it is fully stock and a SB Duramax, with the ally. I have 6k miles on it now, and I hand calucalate the mileage, even though its within .3 to .5 of the DIC for my normal everyday driving.

On a recent 220 mile trip that was under what I consider "controlled" conditions, I got an average of 17.65 MPG with the cruise set at 75 MPH for nearly all those miles.

I of course hand-calculated and filled until I saw clear diesel at the filler neck. I consider this a true estimate of highway MPG because I filled the tank to the top of the filler neck before I left and then filled at exactly the same pump to the same spot upon returning. There was almost no city driving and I didn't romp on it and let any smoke roll.

I was using my Predator only on the 40 HP setting and using FP60 fuel additive.

This is as true of an estimate I can obtain myself. I would like to do the same trip in the same manner at 65-68 MPH to compare results.

So far the best I can get is 15mpg? Only have 5k miles so hopefully it'll get better.

Just a little FYI, you will be able to extend that hi-way mpg to 75 (or close) with a 285 tire.
What's the "no more fan" deal? Did you get rid of the noisy fan somehow?

yet another mpg thread. How fun. Is anyone over 21 mpg actually hand calculating? Just curious.

Yes I am over 21 mpg this past weekend to and from North Carolina.

I just got back from a trip from North Carolina. I drove down running most of the way doing 75-80 and some around town driving for a total of 431 miles before I filled up 19.888 gallons of fuel.
Therefore yielding me 21.6 miles per gallon for the trip down and around town.

My trip back was driven at a more leisure pace only five miles over the speed limit, mostly 65-70 MPH for 311 miles of highway driving. At fill-up it took 13.1 gallons yielding me 23.7 miles per gallon for highway driving. Not too bad for a big old seven thousand pound truck.

Melvin

Impressive Melvin.

Tigermax, just a few mods I worked on recently. Not gone but mostly silenced, except a bit when towing. I'd say 80% gone. The other 20% is quieter.

IMHO the only way to calculate MPG's accurately is like coyotekid posted: fill er' up til you see diesel in the filler neck, let it foam down, slowly fill to tube two more times (but not too full), divide miles driven by gallons used and wallah! Adjust for tire size as needed. Before I started filling the tank this way my mpg's were all over the place, e.g. 17-23.84mpg highway; 13-16mpg city. Now I'm fairly consistent at 15-16mpg city and 18-19mpg highway. Haven't checked unloaded since cold air mod and stack sealing, towing I've improve a minimum of 2-3mpg. Gotta do that. JJ

IMHO the only way to calculate MPG's accurately is like coyotekid posted: fill er' up til you see diesel in the filler neck, let it foam down, slowly fill to tube two more times (but not too full), divide miles driven by gallons used and wallah! Adjust for tire size as needed. Before I started filling the tank this way my mpg's were all over the place, e.g. 17-23.84mpg highway; 13-16mpg city. Now I'm fairly consistent at 15-16mpg city and 18-19mpg highway. Haven't checked unloaded since cold air mod and stack sealing, towing I've improve a minimum of 2-3mpg. Gotta do that. JJ
Each time I fill my tank, I fill until I see clear diesel fuel, no foam, at the top of the filler neck . . . each time . . . every time . . . all the time since the truck was new.
After the Predator @ 65hp and over 27000 miles and just recently, the mileage has creeped up to over 22mpg.
IMHO, I think driving habits, the Predator, and over 27,000 on the truck, has a lot to do with my recent fuel mileage.

MH, are you running any of the overheating mods, e.g. stack seal, shrouds and cold air intake? At 80mph 21mpg is well above the norm for the LLY. You may have the right prescription for mpg's, JJ likee that. JJ

From my experience the outside air temp has made a big deal with my mileage. And of course speed anything over 60mph it drops fast.


Just wondering on the long road trips is it better to go 60 and fuel up once or go 85 and fuel up twice?

Other than the cost factor who gets there first.

It might be interesting to note the stops along the way. We have found that driving 500-1000 miles non-stop will net far better mpg than stopping every 200 miles. I drove from Kansas City to Dallas non-stop one time and got my best mileage ever on that truck. And yes we have aux. fuel tanks.

MH, are you running any of the overheating mods, e.g. stack seal, shrouds and cold air intake? At 80mph 21mpg is well above the norm for the LLY. You may have the right prescription for mpg's, JJ likee that. JJ
Hi JJ,
I have not as yet done the stack seal. However, I do plan to do this mod as soon as I can get the templates.
Other than being over 27,000 miles on the odometer and the 65hp predator I am at lost for the increase in mpg.

Monday I drove from York, SC to Denver NC then to Robbinsville nc with 3 passengers in my long bed 2500 4 x4. I didn't have my juice hooked up due just back from dealer.
I drove carefully, to try for the best mileage..it was mostly at 55mph.
when I filled after the first 125 miles, my DIC showed 25.9mpg but calculator showed 20.5....This is my best mileage ever. (I now have just over 15000 but previous hi under my normal driving was 16 to 17 tops.)

On the remaining 200 miles of the trip, I ran mostly in NC mountains on I40 at the speed limit of 70mph and did a little city driving. This time my DIC showed 20.8 but calculator was 18.4.

I'm very happy with these numbers. Next time I go to the mountains I'll drive same speeds but with the juice a setting 1 to see change.

Happy trails

MH, are you running any of the overheating mods, e.g. stack seal, shrouds and cold air intake? At 80mph 21mpg is well above the norm for the LLY. You may have the right prescription for mpg's, JJ likee that. JJ
JJ, I forgot to say that the latest mod to my truck was the 3" OEM air dam extension. So far I have not sealed tow hook area yet. I bought two from the dealer and we ordered them for Peetie-pie's Avalanche and they will not fit my 2500hd.:D

:)

This is my first post, and first diesel. I have an 06 Duramax 2500 crew cab SB LLY motor and just barely broken in the built in computer averaged 21.1 mpg, however hand calculated I (still cant believe it) did closer to 23.6 mpg.

:)

This is my first post, and first diesel. I have an 06 Duramax 2500 crew cab SB LLY motor and just barely broken in the built in computer averaged 21.1 mpg, however hand calculated I (still cant believe it) did closer to 23.6 mpg.
Yours should get better in time. After 27000 I can really see a difference. Just wait until you put in a performance tune and larger exhaust.

i have an 04 4 wheel drive extended cab gmc the best i get in city stop and go is 14.5
and 17 to18 on highway i live in fl and drive easy trying to get the best fuel mileage
at 3.10 a gal pulling my camper i get 11mpg city or highway

I got 2000 miles on my 06 lly and the dream meter says 18mpg and hand calculated 17.8. I have 265 tires on it. So I would be getting more than 18 but dont know how many miles to add after fill. Maby 5miles per 100 miles?? Anyone??

My hand calc last tank was 18.8mpg, mixed driving. Added 4" muffler, will see if this goes up, HP definitely did. Reset DIC, It lied to me and said 23.8 on highway. Also 4wd.

Mike

I still can't figure out how people get such good fuel mileage.

I drove 240 highway miles this weekend.

Kept it between 72 and 74.

I got 15.5 mpg hand calculated.

Hmmm.....


I used to wonder the same thing. I found it to be a factor of milage. I'm just a hair under 11K w/an 05 2500HD and my milage is taking off. Used to get around 15~ when I first got it, of course that was in the winter with fast idling and winter blend. Now I'm getting about 16.5-17mpg around town, and did 20-21mpg on I91 to and from VT. Highway was between 68-75MPH. Most of my city driving occurs around 1500-1800rpm. I'm also running the stock 245's. The milage didn't really start taking off until I broke about 9K miles.

I drove up to Onaway,Mi. on Monday & returned Friday. Set c/c at 2,000 R.P.M. = 68 M.P.H. & went 367 miles on 17 .2 gals. 21.34 M.P.G. Filled up as the rest of you do at a "Flying J" $2.68 on way up & $2.75 on way down. 2002 2500 CREW CAB - Stock 125,000 miles. Love that truck!!

I used to wonder the same thing. I found it to be a factor of milage. I'm just a hair under 11K w/an 05 2500HD and my milage is taking off. Used to get around 15~ when I first got it, of course that was in the winter with fast idling and winter blend. Now I'm getting about 16.5-17mpg around town, and did 20-21mpg on I91 to and from VT. Highway was between 68-75MPH. Most of my city driving occurs around 1500-1800rpm. I'm also running the stock 245's. The milage didn't really start taking off until I broke about 9K miles.
I run the stock 245's with a highway tread pattern inflated @ 65 lbs. all the time empty or loaded.
The ride is good the tire treads are wearing even across from side to side, in fact the front tires looks as even across the tread pattern as the rear.
I think the large mud & snow 285's and larger tires, speed over 70 mph, and jack rabbit starts, (driving habits) greatly effect overall gas milage.

http://personal.linkline.com/rlockyer/2500Gas.xls

Ya... I know, the D'max doesn't take "gas", but the original spreadsheet was "TundraGas" and I couldn't think of a better filename.

this weekend i drove from tampa,fl to just outside nashville,tn and back (stock tires) i averaged in the low to mis 13's mpg period (hand calculated) DIC lies badly saying in the low 20's mpg :( i went around 70~74 most of the way there, and 60~70 back towing around 10k (milage didn't drop much at all)