I have had my truck two years now and have about 26K on it. This is my first diesel. I have re-engineered many of GM's shortcomings out of my truck. I run a mix of Total Power FPPF and 8+ in every tank, have the Mega, a lift pump, Amsoil in a modified airbox, a Magnaflow muffler, 125 HP Juice set to 5/5, a 4" lift and BFG AT KOs in 295/75R16. Here is what I am noticing regarding fuel mileage.


- Best mpg on freeway 21.9 w/285s, 2" of t-bar crank, and 90 HP Juice (before I installed the lift) in the late fall in South and Central Texas. City MPG seems to run 14-14.5.


- Fuel mileage is very dependent on fuel quality


- Winter fuel loses about 2 mpg on the freeway


- Best mileage is with summer fuel in cool temps. I think this is because it keeps the fan clutch from engaging


- At speeds over 70mph, fuel mileage really starts to decrease.


- The Juice setting doesn't seem to affect mileage if you are gentle with the pedal.


- The truck's mileage is poor until around 5K. At 18-20K it makes another big jump in mileage. I expect a truck used for towing right off the bat would break in more quickly.


My last two city driving mpgs were 14.0, and I was fairly heavy footed. My last two freeway trips were interesting. With fuel from my normal place (TETCO), I got 19.1 mpg, over 4 hours of driving that included 45 minutes of idling through traffic jams. The last time I had a similar amount of idling, when I came home without any traffic jams my mileage was up about 1.5 mpg. However, coming home today was a surprise. I was expecting 20-21 but wound up with 17.5. The only thing I can attribute this to is Wal-Mart gas--I guess there is a reason it was under $1.60--and the 100+ degree temps on the freeway keeping my fan clutch engaged much of the trip.


What have you guys seen?


BlaineEdited by: afp1

in my first 3 tanks i havent had better than 15.7mpg My driving habits havent been great however either....idle periods quite afew 2,3,4 mile drives then shutoff....http://www.dieselplace.com/forum/smileys/Disapprove.gif but after stopping into the dealer, and looking through the previous owners work orders, it appears as tho the FF hasnt been changed since leaving the factory...putting it at 25K....im thinking/hoping that this will help my mileage....My fuel comes from a distributor who fills up our few thousand gallon tank at our farm...

Polarbear,


Sounds you are doing all city type driving to me, and if so, 15.7 is very good. A true freeway trip will be almost all cruising at speed. What is an "FF"? I calculate my mileage by dividing miles driven vs fuel used. I am not sure the driving computer is all that accurate, but I don't have one.


Blaine

03 CC Alli with 28K miles and 265 BFG KO's. I run stanadyne DFA on every tank. I recently upgraded to the Banks 6-Gun. Before the 6G I was getting 16-16.5 city and 18.5-19hwy running 75+ MPH. With the 6G on setting 4 I'm now getting 17.5 city and 19.5-20 Highway. On the rare occasion I drive 65 I can get over 20 but it's hard to do that on Michigan freeways. My MPG was lower during the first 8-10K miles. I have not noticed a big difference in MPG based on where I buy fuel, but in all fairness I buy 80-90% from the same location.

AFP1- FF =Fuel Filter....I calculate my mileage same as you, i dont have the DIC feature...I did find that when filling up, i wasnt filling all the way.Id fill til it started to foam up the neck of the tank, then call it quits...in 30 miles my gauge was already below Full...Well the last few times, ive been filling so i can see acutal fuel down there...I got close to TWO more gallons....

It seems many of us get the best and most consistent mileage with fuel from the home pump. I wonder if this has to do more with getting a consistent fill point each time?

FWIW, regarding the home pump and getting a consistent fill, I've noticed that it can even make a difference using the exact same pump but parking on the other side of it. The slope that the truck is sitting on can effect the pump's detection on when it thinks your tank is full.


I use the same pump and park on the same side every time with my fan (I fill it every morning) and I found that if I park on the other side, it will click off about $2 short. When I fill up on the "normal" side the next morning it costs $2 more than normal before the pump clicks off.


Parking on the same side every day it seems to click off at the exact same fill point every time, no need to top it off to be accurate.


I've compared my DIC to doing the math manually and found it to be extremely accurate to within ~.2 mpg's, so I just trust what it says (except for if I use the Juice).


With stock tires I had an all-time best of 25MPG, on a 300 mile return trip of two-lane highway with speeds (speed limits) consisting of half 55mph and half 60mph. This was actually when the truck was almost brand new, maybe 1500 miles on it at the time.


I put the 315's on soon after that and the best I've gotten with them is 22MPG doing the same trip.


I've never paid much attention to my fuel mileage when the Juice was plugged in, didn't seem to be too much worse than normal (it fools the DIC into thinking it's getting great mileage) but I couldn't keep my foot out of it.http://www.dieselplace.com/forum/smileys/Embarrased.gif


I know I'm in Canada so you're all probably thinking these numbers are using the imperial gallon but the DIC measures in US gallons when set in English mode, even on Canadian trucks.

On a recent run to Colorado without my trailer I broke 20 MPG on the 2 lanes cruising 70 or so. That was with the juice on level 4. I tried running a tank with the Juice on level 2 and got worse mileage. On the return home mileage was crappy had a constant 20+ MPH headwind with gusts to 30MPH.


I usually run 80-85 MPH empty and a run from L.A. to Yuma on hwy. 8 with lots of grades I got 18.5 MPG. Truck has 17,500 on it now but I have never seen a jump in MPG during break in.