Amazing MPG gains... Magic fuel, or ???

[msiminoff]

I have driven 6975 miles since setting out on this cross-country trip back in early October, and I have recorded every single mile and each gallon of diesel fuel along the way (22 tankfulls so far) in my log book. On average I get a hand-calculated 11.65 miles per gallon and the overhead console's "Lie-O'-Meter" usually displays ~14.4 MPG. I do always fill my tank all the way up to the top of the filler neck.

However on three separate occasions (over 4 tanks of fuel) I have gotten much much better fuel economy... in the neighborhood of 13.55 MPG (and 17.0 showing on the overhead). That's an unbelievable 16% increase!!! To make things more interesting, while getting better mileage, the truck feels more "peppy" and it seems to smoke less too.

The first time this happened was near White Sands NM (fuelled-up at a Texaco station). I had just adjusted the rear tire pressure (from 105 up to 115)... and we had traveled to a slightly lower altitude over the course of the day. So I just assumed those things contributed to the improved economy.
The second time it happened I was driving across west Texas at a constant 65 MPH and there was almost no change in elevation. I chalked that one up to my gentle use of the skinny pedal.
Now this third time I am in the Florida Keys (= sea level). I drove down here from the Palm Beach area and got my usual ~11.6 MPG, but after fueling up the overhead display suddenly started lying to me again and displayed 17.0 MPG. Sure enough when I refilled the tank, I got 13.5 MPG.

Now here's the really interesting part; This is the first time I have re-filled at the same gas station twice in a row (a Chevron in Marathon FL, in case you're wondering). On the second tank I drove up to Miami and back and low and behold I got the same improved fuel economy (both directions). Same roads, same speeds, same elevation, same temperature and humidity levels, same weight on the truck, etc.
One very interesting tidbit is that the diesel pump at this particular Chevron has a sticker on it that says " Fuel contains up to 10% ethanol". Hhmmmmmm ???

So... what's going on here? How can it be possible that some occasional fill-ups yield 16% better economy, yet all of the others are super consistent? Any chance that some gas stations are selling better diesel fuel that others? Is it my driving? Altitude... speed, weather conditions? Could I be getting a winter diesel blend? Defective odometer? Is this just a fluke?

And what's the chance the addition of ethanol has somehow helped? This seems unlikely to me since ethanol has far less BTU's/gal than #2 diesel.

I sure would like to be getting this improved fuel efficiency all the time.
I am stumped! Please share your thoughts.

Cheers
-Mark

[rider997]

msiminoff wrote:


Here's something to noodle on... What has a higher energy density than #2 diesel fuel?

Per liter, Kerosene (Jet fuel)

[mooring_product]

Was heading home from work. We don't see many truck campers in S Fl.
Good looking rig.

[msiminoff]

mooring product wrote:
Is this you? You in Pompano Beach?

Yup that's me!!
Currently in Ft Lauderdale and off to the Everglades this afternoon 🙂
-Mark

[Bob__B]

The mileage on my truck varies a lot based on wind direction and how fast I drive......but sometimes has significant deviation when it seems like it shouldn't.

I have always thought it might be DEF regen causing it ..... but that wouldn't be the case with the older diesels.

[bka0721]

mooring product wrote:
Is this you? You in Pompano Beach?
Untitled by MooringProduct, on Flickr

Yes, that is Mark's Truck (msiminoff) and Camper. He posted a thread about the stackable blocks to level out his truck with. You can see them on the left side of his bumper, as well as the rest of the truck camper is matching his camper, as well.

b

[ReneeG]

Sure looks like him with that green triangle in the rear window.

[mooring_product]

Is this you? You in Pompano Beach?
Untitled by MooringProduct, on Flickr

[jefe_4x4]

Mark, it is a mystery all right. Unexplained great MPG.
I"ve only had one experience like that. Jeanie and I were driving from Sand Point, ID to Seattle, against the prevailing westerlies, uphill, and the gauge was barely moving. I thought, "Wow, this is great". I have the same size tank as yours was, stock and we traveled a couple hundred more miles that I thought possible, still watching the gauge like a hawk. We were going south on 5, north of Portland and hit a slight uphill when the engine went dead-pedal. Coasting over to the side, a couple hours passed before we could get towed to a Dodge Dealer. Within a couple hours they got to our rig and the tech said we were out of gas. What? He had simply thumped the plastic tank with his middle finger knuckle announcing that is was dead empty. He walked across the street with a couple jeep cans the contents of which were poured into the tank. He bled the injectors and fuel filter by cycling the lift pump. Of course, it started right up. No harm; no foul. The problem was the fuel sender. It was replaced later.
The biggest MPG detractor from my experience has been wind resistance. Some trips on the flat with a good tail wind have given us over 15 mpg with a loaded, 10K pound rolling white box.
I do agree that there is some variation in quality of No. 2 diesel fuel sold in the US. What is that value? Heptane? I would think if Diesel fuel is infused with corn oil, and had fabulous results, people everywhere would be flocking to it.
Also, I notice diesel TC's with more torque and HP tend to have a smaller variation in MPG. Our tiny little 245 HP/505TQ HO Cummins, which was the bomb in 2001, is now on the low end of power, compared to the newest offerings, and more susceptible to wind and hills.
jefe

[JimK-NY]

Driving long distances on the open road with cruise control I can get around 11 mpg with a head wind and up to 16 mpg with a tail wind. Actually I go 17 mpg once for an entire tank when driving across Nebraska with a strong tail wind. Somehow it usually seems that I am bucking a head wind but I guess that would be driving a round trip with both directions uphill.

[Pete_k]

As for difference in where you fill. I fill the same side, same pump. But I do hold 150 gallons. So even if we drive to the Gulf Coast, I can come back home. Then fill up at the same pump. Stick the nozzle into the tank the same distance each time. When the pump shuts off its done. Today filled up for a nice $1.54 cents per gallon.

[Kayteg1]

One more thought just come to me.
Bio-diesel and alcohol are renewable sources, but are not cheap.
I wonder if the blends that used to have 10% of that stuff, now with crude pricing dropping down are getting closer to 100% of mineral fuel.
That would explain higher mpg, while not all refineries will do it at the same time.

[Pete_k]

How many miles are on the engine?
When they get broken in better MPG can and does happen.
As for the sticker on the pump. That is on most of them, but no corn juice was added to the fuel. Bet the sticker has "may contain up to 10% ethanol" ? They do that to cover there rears. And most fools stick in on every pump. Shoot our 100% gas pumps had them on there.
But along the same lines, my 5.9 24 valve has also jumped up in MPG. Better then yours. But I did have to get a new head gasket. Thus a overhead was done on the truck. And mine is getting way better now also.
Pete

[Liketoroam]

not a truck camper , but on my class b I once got over 18 mpg ironically filling up in N.M. It happened once and I check mpg every tank. The only thing that was different was a bad battery connection, that I had to wiggle to start the van. Maybe computer was acting up in my favor. It wasn't the amount of fuel ,but the number of miles driven that was mind boggling.

[covered_wagon]

I've seen 15 miles to the gal. hand calculated with my CTD at 3400 lbs.

I can only do that on lonely back roads going 50 MPH. I never go by a train schedule nor Interstates.

I get there relaxed and happy, thanking God there is a place for fast drivers on the Interstates.:)