Inconsistent Fuel Mileage

[RCovert]

I have an 04. 5 3500 4x4 dully, QC, SLT, 325/600, 48RE, with 3. 73 rear end. When I bought it, I was getting 13/14 around town and 17/18 on the highway at 1850RPMs (about 68 MPH) empty. When truck had 700 miles on it I started towing our boat (triple axel trailer and boat weigh 10,000+) got 13. 5 MPG.



Then the damn turbo went out at 4000 miles – after they replaced it I started getting 8 to 9. 5 towing and 13. 5 to 15. 5 on the highway @ 68MPH empty. The truck was in and out of the shop half a dozen times and they could not find any reason for the drop in mileage. In September I found out about TSB 18-037-04 and called my local service man and he had just received it. I took my pickup down and had the flash done. The next day we went on a 2400 mile trip (80/20 highway/town) and averaged 17. 5 MPG. Which, made me a very happy camper. I was in love my dully, again.



The Love story didn’t last very long. Three weeks later I started to notice that I was getting a real variation in fuel mileage on the road. The mileage is hand calculated and reflects highway miles running @ 1850RPM (about 68 MPH) empty. The worst mileage was 11. 6 and the beast 19. 1. The average variation per tank of fuel is between 13 and 18MPG. I’ve got 17,000 miles on this darn thing and I've been having fuel mileage problems for 13,000. Would appreciate any help/ideas anyone has. By the way, I’m still getting 13/14 around town.



Thanks

Ray



Additional driving condition info – most of my freeway driving is on I-5 Northern California which, has a few hills but is relatively flat and I monitor the boot. On the level @1850RPM the boot is normally about 8/9 and naturally climes up when going up a hill or incline but come back down as some as it levels off. When the boot is in this range the fuel mileage average is around 18/18. 5 and the overhead reading is very close.



Again, I monitor the boot very closely and I’ve noted that sometimes after making a short stop and getting back on the freeway, I set the cruse @1850RPM and running on the level the boot will be in 12/13 range and clime up to the 22/26 when going up a little hill or incline and when it levels off it will only go down to the 12/13 range. When the boot is in the higher range, the fuel mileage drops down to 12/13MPG and the overhead is off, showing that I’m getting 2, 3 or even 4 miles more than actual hand calculation.



Two weeks ago I drove from Portland, OR to Red Bluff, CA – the boot was in the normal 8/9 range. I fueled up and the average from Portland to Red Bluff was 18. 8MPG and the overhead read 18. 9. Pulled back on I-5, set cruse @1850RPM, about 80 south of Red bluff I noticed the boot go up to 13/14 on the level. Check the overhead and it was reading 18. 2. I continued at the same speed for another 250 miles and stooped to fuel. The overhead was showing 17. 1 and the actual hand calculation was 13. 2 (sorry, I can’t type – that should be 15. 2MPG). Also, when the turbo boot is high and the fuel mileage is down/poor the rear fender of my white dully is BLACK. Which tells me that the ECM is feeding more fuel than the engine can burn.

 

[Udaloy]

Ray,



Before too many people get on here and tell you that they get 22-24 MPG, and that something is very wrong with your truck, you are in the majority. Your variations are cause for a little concern, and I understand that's the thrust of your question. In my opinion, and experience, the three things that kill mileage more than anything else, is a heavy right foot off the line, extended idling, and inconsistent filling of the tank. I've written down the figures at each and every fill up since new. filling it to the brim (which takes an extra five minutes) every time. To date, I've averaged 16. 6 over 15,000 miles.



This is mostly empty driving 50/50 70 miles to/from work everyday. It seems like I can't go a full tank without hauling at least an empty 18' landscape trailer. There was a trip to Martinsville, VA with a 40' 5th wheel, and about a 50 mile trip with my Allis-Chalmers 210 (20k GCVW). The trip to VA netted me 10 MPG. After thinking it over, I'd say the biggest factor is in how you fill the tank. It's easy to change the numbers by two gallons. JMHO.

 

[JPereira]

Ray,

You may want to think about the vent kit that a fellow TDR offers. It makes fillups a joy and helps be more consistent with the fillups. I am going to try and paste a link to the thread.

Vent Kit thread



If the link doesn't work search for:

Improved fuel tank vent kit.





Hope that helps. I added this and am glad I did.



Jeff

 

[Motobeagle]

I recently took a trip from Chicago to AZ pulling a lite aluminum twin axle trailer. There were two sportbikes in the bed of the truck and two in the trailer with about 200lbs of gear. Overall it couldn't have been more than 3 ton aerodynamic load.



I kept the speed at 75-80 with some short instinces of 90+ while not paying attention.



I was upset to see my rolling average in the neighborhood of 9 mpg +/-.



The original thought was cold temps or poor grade 2 fuel. After I got home and got some fresh oil the mpg shot back up to 15-17 average (without the load).



I'm driving an 03 HO with 373 gears, but need some throttle control.



Hopefully the 305/70/17 Goodyear MT's (on order) will help a little.

 

[BrentKaiser]

Ray,



In my opinion, and experience, the three things that kill mileage more than anything else, is a heavy right foot off the line, extended idling, and inconsistent filling of the tank.

I agrre totally! I average 7-9 MPG city during the winter because of very long idle times. I live in Alaska and park outside, so when it gets -30 or -40 outside, my truck sits and idles for what seems like days. I also have a very heavy right foot. It is a blast to watch all the cars behind you disapear in a cloud of exhaust from it being so cold outside. Sorry I got carried away, just wanted to say I agree!

 

[PJ]

With 6k on my truck now, my city avg is just above 15. . My highway is 19. . These are unloaded figures with nothing above 70mph. A bit less than my 04 but, anything above the 10 my 97 Powerstroke got is great

 

[RCovert]

Additional driving condition info – most of my freeway driving is on I-5 Northern California which, has a few hills but is relatively flat and I monitor the boot. On the level @1850RPM the boot is normally about 8/9 and naturally climes up when going up a hill or incline but come back down as some as it levels off. When the boot is in this range the fuel mileage average is around 18/18. 5 and the overhead reading is very close.



Again, I monitor the boot very closely and I’ve noted that sometimes after making a short stop and getting back on the freeway, I set the cruse @1850RPM and running on the level the boot will be in 12/13 range and clime up to the 22/26 when going up a little hill or incline and when it levels off it will only go down to the 12/13 range. When the boot is in the higher range, the fuel mileage drops down to 12/13MPG and the overhead is off, showing that I’m getting 2, 3 or even 4 miles more than actual hand calculation.



Two weeks ago I drove from Portland, OR to Red Bluff, CA – the boot was in the normal 8/9 range. I fueled up and the average from Portland to Red Bluff was 18. 8MPG and the overhead read 18. 9. Pulled back on I-5, set cruse @1850RPM, about 80 south of Red bluff I noticed the boot go up to 13/14 on the level. Check the overhead and it was reading 18. 2. I continued at the same speed for another 250 miles and stooped to fuel. The overhead was showing 17. 1 and the actual hand calculation was 13. 2(sorry, I can’t type – that should be 15. 2MPG). Also, when the turbo boot is high and the fuel mileage is poor the rear fender of my white dully is BLACK. Which tells me that the ECM is feeding more fuel than the engine can burn.



Thanks again