RickG

The lasted issue of "Land Line " magazine published by OOIDA has an article about a truck owner that had a problem with poor fuel mileage he was unable to solve . Then he noticed the high temperature of the fuel at every Flying J he fueled at . He switched fuel suppliers and his mileage improved . OOIDA investigated fuel temps at various fuel stops . Flying J fuel temps averaged 30 degrees higher than fuel at other stops . About a month ago I quit buying fuel at Flying J . I had been buying fuel at Flying J regularly for my '04 3500 DRW delivering RV's . I had ben getting a consistent 10 mpg loaded . When I quit buying fuel at Flying J I got a consistent 12.5 mpg loaded although at the time I thought it was due to the truck being recently serviced .

DSjockey

Wow thats a big gain, why would their fuel be warmer? I've been getting mine at Flying J too, maybe I'll try a change

mainer

Thats odd that it was hotter, usualy running K1 or part gas makes it run hotter.

coop

RickG

Ever notice if you fill your tank in the summer then park it overflows ? Fuel expands when heated . If a tanker delivers fuel in colder weather and the storage tank is heated the fuel will expand the same way it does in your tank . When it gets in your cooler tank it decreases in volume . All the Flying J fuel OOIDA tested was over 85 degrees . Fuel at other stops was all under 60

infidel

The mpg claim doesn't make any sense at all to me since the fuel is going to get hot anyway.
Out of curiosity I once measured the temp of my cold tank bottom with a infrared temp gun. It was the same as the outside temp, 20°F
42 miles later it was 112°, the outside temp was still 20°
This is due to return fuel doing it's job, cooling the injection pump.
On another occasion after a long trip in summer my fuel tank was 175°

I read a scientific paper not long ago where fuel temp was compared to engine efficiency (mpg, power) in a lab with Caterpillar engines. Peak efficiency was reached with 370C (about 700F) fuel at the injector.
Highly doubt Flying J or any other station fuel ever exceeds even 100°.

nickleinonen

pump hot fuel into your tank and you will have less fuel in there than if cold fuel was pumped in... i don't think it would be enough of a difference to notice like 2mpg, but there would be a difference... most places around me, have calibration stickers on the pumps, stating the pump is calibrated to read correct at like 20°C, so above that, less than amount, below that, more than amount...

infidel

OK Nick, I can go with that, but you aren't really getting better mpgs at all, you're just being able to get more fuel in your tank with cooler fuel.
So in essence Flying J's gallon is less than others.
It still seems rather odd their fuel would be that much hotter if it's stored in an underground tank where the temp is a steady 55F. I doubt they would heat it to cheat people on the gallon, it would cost more to heat it than they would gain.
The whole thing seems fishy to me.

GOINDOGE

I like to fill in the mornings (gas, not diesel yet) so I can feel like I am getting my monies worth.. Been doing that for years... Don’t know if it good or bad, but if it is going to expand, at least I got contracted...

Lightman

Infidel, that's odd. I thought I saw a similar chart related to fuel temps, and I thought I read the best temp for diesel combustion was around 80F. I'd love to find out.

Also do you think your temp gun is getting an accurate reading on the fuel, or just the outside of the tank itself? That seems awfully hot.

F. Flack

I'm with Infidel -- this doesn't make sense. On the surface, it seems that you would be getting "less fuel" when pumping warmer fuel (and paying for what you are not getting). In order to get an increase in MPG from 10 to 12.5, the fuel would have to expand from 1 gallon to 1.25 gallons (based on the same distance traveled between fills). It's been a long time since I cracked my Physics book, but that doesn't sound possible -- especially with only a 30 degree change in temp. It would be easier for me to believe that fuel quality caused the change in MPG.

Gear Poet

Perhaps the fuel quality is related to the heat? Some additive or substance that creates a chemical catalyst within the fuel? Degrading it, with heat as a byproduct?

Lary Ellis (Top)

This is the reason I cringe everytime I read a post from some guy trying to get as many miles out of a tank of fuel as he can before filling up. The lower the volume of fuel in the tank, the higher the temps will climb as heat is transfered from the Injection pump and sent back to the fuel tank.

That simply means your Injection pump is running hotter,......heat bad...... Cool good...

I never let mine fall below 1/4 tank, especially in hot weather. This way the IP stays cooler and you don't suck up the dirt and contaminants like water, that collect at the bottom of the tank.

infidel

Lightman, I think it would be impossible to have 80° fuel at the injector on any diesel engine except for a short period after a cold start. Seems that just the act of compressing it to around 20k psi would heat it considerably. I'll try to find the article but as I recall the testing didn't even use fuel cooler than 38C (about 100F)

I'm sure measuring the outside of the tank is just a rough indication of how hot the fuel is but when it's 20° outside if anything the tank temp would be reading cooler than the fuel.

I'm with Larry, I rarely let my tank drop below half.
If anything it goes long enough where it's time to stretch your legs at half tank.
I think fuel cooling is what Dodge had in mind designing the gauge to read empty with 7-10 gallons left in the tank.

Haulin_in_Dixie

Bill you need to restate that one. A liquid does not compress. The heat is caused by the pumping, not compression. Air or a gas is compressable and creates heat in the process.

I have noticed that my fuel mileage when fueling at Flying J is not as good as other stops. It used to be better.

RickG

I e-mailed the writer of the article to get more info . The magazine is mailed to OOIDA members and is available free in some truckstops . There is an online version of the magazine but I couldn't find this article in it . Fuel temp checks were done in April at the folowing Flying J's : Louder , S.C. -85 degrees ;Temple , GA -87 degrees ; W.Memphis , AR -93 degrees . On the same trip fuel checked at a Petro in Weatherford , TX was 53 degrees . Flying J representatives refused to respond to calls regarding this . The main driver featured had his mileage drop to 4.3 mpg while using Flying J fuel and it went to 6.2 after switching to other fuel . I noticed in the past month Flying J prices are no longer lower than those of other fuel stops . It makes me wonder if they quit doing what they got caught at so they charge the same as everyone else when they don't cheat .