Curses on you, fuel pump!

[Diesel_Dave]

Okay, so here's an update.

I'm now convinced that the fuel pump was correct, that is I DID put 37.5 gal in the last fill up. One factor that convinces me of this is that I went 300 mi before getting to the "F" mark. Also, I just filled up again this morning. I went 1,243.3 miles on this last tank! Filling up this time (again until I could see the fuel level in the neck), I put in 34.2 gal. That's pretty much what I would normally expect. My "low fuel" warning had just come on the overhead about 15 mi earlier. In the past I know I've gone about 30 mi after that and filled up with about 34.7 gal.

So, the pump was correct, but somehow I put an extra ~3 gal in last time. That means my 3-tank, 90-day, & lifetime FE are all correct now--it's just that the calculated FE for these last two tanks are skewed in favor of the latest tank. Nominally they're 28.6 mpg & 36.3 mpg, respectively. They should be about 30.8 mpg & 33.1 mpg. Those numbers make a lot more sense with the trends I've seen from my in-cab display.

[OneOfFew]

I've had something like that happen before, where the pump measures more fuel then it actually pumped. In my case it was because the tank was running low and pumped some air through with the fuel. I could hear the pump speed up as the air was going through it. It happened to a guy at another pump at the same time.

[Diesel_Dave]

Boy, that must have really stunk. Not only becasue you paid for fuel that you didn't get, but also because Lord only know the junk that's in the very bottom of the tank.

[redpoint5]

I am envious of those FE numbers DD.

I'll blatantly thread-jack by asking which year of the 2500 has the best potential for good FE? I was thinking 2003-2004.5 since these years went common rail but was pre-cat.

I have a '98.5 4x4 that gets terrible mileage due to a used up tranny. It used to get about 20mpg. Impossible to tell what I'm getting now with larger diameter tires and a broken speedo/odo. Perhaps 14mpg, which I cringe at the thought of.

[Diesel_Dave]

Originally Posted by redpoint5

I am envious of those FE numbers DD.

I'll blatantly thread-jack by asking which year of the 2500 has the best potential for good FE? I was thinking 2003-2004.5 since these years went common rail but was pre-cat.

I have a '98.5 4x4 that gets terrible mileage due to a used up tranny. It used to get about 20mpg. Impossible to tell what I'm getting now with larger diameter tires and a broken speedo/odo. Perhaps 14mpg, which I cringe at the thought of.

I really don't think there's a huge difference in which model year has the "best potential". Honestly, I would say driving style plays a bigger role than anything else. That being said, certain things influence that--running trucks with a DPF in a good-for-FE manner is almost impossible without causing DPF problems from it being too cold. Of course, all the fuel it takes to regenerate the DPF will kill you're FE as well. 4WD and an auto tranny will negatively impact your FE as well. The introduction of EGR hurt FE as well. Of course EGR, DPF, and cat can all be removed (not legal, but it can be done).

As far as your larger tires, I wouldn't think those would kill your FE (depending on how big you have them). All else being equal it would decrease you cruising rpm which might actually help your FE. When you say your speedo/odo is "broken" do you mean broken broken or just not reading correctly?

[slowmover]

I have the 305/555 motor (late 2003-early 2004) which I believe is the last excellent choice for simplicity due to lack of emissions controls, but yet is run by the HPCR (high pressure common rail) system and other significant benefits of the Third Gen trucks (2003-2009). No third injection event, catalyst or other as began with the 325/610 engines in late 2004 (mid-December production dates); often referred to as 2004.5. The 6.7L engine shows up in latter 2007, and, while it is more powerful, with some excellent changes, one must delete the emissions devices (physical removal) and add aftermarket tuners to control engine performance in order to achieve 20+ mpg hwy. 24-26 mpg in the South Central US, driving at around 60-mph is not uncommon for these, dead-stock, with 2WD and the NV-5600 6-speed.

I can run 7,500-15,000 mile oil/filter changes, for example. This drops like a stone with the third injection event added for 2004.5. Stick with 2WD for better road performance and far greater reliability of front end & steering components. Larger tires and auto trans really hurt FE, as does 4WD. The added increases in maintenance and repairs of those options -- over a B50 lifespan of 350k miles -- make for a much more expensive truck to own. The addition of lift kits, oversize tires, etc, makes for a much higher operating expense per mile, not just an FE drop.

1,200+ miles on the stock tank is really impressive!

.

[gone-ot]

...although this is more of a seasonal issue, consider how much the same volume (gallons) of fuel can expand between HOT and COLD temperature extremes, which will affect how "quickly" the gas tank can appear to become full.

...anybody know the expansion rates of gasoline and diesel?

[Diesel_Dave]

Originally Posted by Old Tele man

...although this is more of a seasonal issue, consider how much the same volume (gallons) of fuel can expand between HOT and COLD temperature extremes, which will affect how "quickly" the gas tank can appear to become full.

...anybody know the expansion rates of gasoline and diesel?

It's about 0.05% per degree F. So with my 34 gal tank, 0 deg F vs 100 deg F means a variation of 1.7 gal (for the same mass of fuel). That's pretty extreme though. A 15 gal tank with a 30 deg F variation is 0.23 gal.

[gone-ot]

...since those numbers were something I hadn't (yet) looked up, your answer prompted me to do some searching. From page 2 of NIST Bulletin B-015:

"...For reference, the widely accepted coefficient of expansion for gasoline is 0.00069/°F and for diesel is 0.00050/°F."

...notice how they illustrate how the fuel level "rises" within the neck of the vessel when the fuel is hotter, making it *appear* to be full, when it really isn't. And, the visual deception becomes more apparent the smaller the neck diameter is versus the fuel tank capacity .

[Diesel_Dave]

Hmm, I'm kinda suprised that gasoline and diesel are so much different.

Just to add another wrinkle, temperature will change the volume of your tank as well, i.e. if the temperature is higher the tank volume will be larger because the tank material has expanded slightly. Of course, as you fill the tank up the tank material will be cooled or warmed by the fuel. And all this depends on the tank material and tank shape as well.

It's interesting how complicated "simple" things like filling up can be isn't it