During the Katrina shortage, the EPA lowered restrictions on sulfer content and batch processing (different specs for different parts of the country) in order to stimulate fuel production. The companies that bought this oil had until January to get it out of thier tanks. My uncle in KY was filling up last month and looked down and was pumping off-road fuel, this fuel was coming from Shell. Oil companies use futures as a common part of thier business. Meaning they Sell High, Buy Low. I'm sure that some companies stocked up on the cheaper, more-abundant fuel while they could and then waited as long as they could to sell it, depending on what the going price was/is.
The sudden drop in fuel mileage could be easily attributed to the last of one of the crappy batches of fuel.
My worst mileage was with a tank of 60% biodiesel and 40% BP/Amoco standard diesel (not altogether unexpected due to the lower BTU content of biodiesel). My best mileage was with a tank of BP/Amoco Premier Diesel.
My area of the country has seen some pretty wide fluctuations in temperature this winter and I'm sure that accounts for a difference in mileage too.
My own personal experiment is to going to be to "standardize" on the best mileage fuel for a few fills and see if things stabilize.
2003 F-250 4X4 Lariat Crew Cab 156" WB, Arizona Beige over Black, 7.3 PSD,Superchips 1705 "tow safe", auto, 3.73 limited slip, X-Monitor, ARE hard tonneau cover, Line-X bed liner, Ford splash guards, vent visors, hood wind deflector, 50 gal Transfer Flow in-bed tank, Powerslot cryo rotors (front) with Hawk LTS pads, Ford AIS with fender sleeve, V3 Back-up Camera, Marinco mod.
Do you have a locking cap for your fuel tank? Sometimes that can help your mileage tremendously.
Hopefully what I'm insinuating is not the case here as you describe your mileage going down and gradually coming back up. If somebody was helping himself to your fuel then your miles per tank would rise and fall suddenly. ..........JIM
2014 F250 Platinum CC Short Bed 4x4, 6.2 (I Got Gas Now!)
2003 F250 XLT CC Long Bed 4x4, 6.0 w/Auto (SOLD)
I have been amazed since owning a diesel, how much the mileage fluctuates. 17.5 summer is about average. Winter about 15 unless it get really cold (zero to +15F) it will drop to as low as 12 and never above 13.5 in that temperature. I wonder if a winter blanket on the grill would help.???
2001, F250 4x4, CC, Auto; Mobil 1 in transfer case&Trans.; Frantz Bypass Filter; "Hutch" fuel mods; Sonnax/Tricum mod; 4" Exhaust, 30" MagnaFlow; Attitude in A-Pillar and tranny gauge in Dash; AIS; EASE Diagnostics; Reese Slider Hitch; Fr Rotors, Cryo Treated&Slotted by ART.
My MPG also wanders around a bit in the winter. Fuel variation may play a part but it seems to happen every winter.
I think driving conditions affect me a lot. To get big MPG, you need to drive smoothly and that isn't always possible in the winter. Goofy drivers, slick roads and poor visibility conspire to make your speed control less than what it should be.
'00 F-350, 4x2, 6 Speed AIC 210,000 miles
Fuel tank mods: MaroonHarpoon, Pre-Pump,
Evans, 203 degree thermostat, Poor Man's Tymar, 4" Single SS Exhaust, Rugged Air Dam
225-75x16E tires in front 235-85x16Es in back, tires aired up to 100 psi, Lowered 4" in front and 6" in back, "Fastback" bed fairing
21.3 MPG before mods
27.0 MPG tested with mods
It's no myth. Over Christmas my family and I drove our 1966 GMC 4107 bus from CO to CA to visit family. I filled up in CO before I left, and got [censored] mileage from here to Arizona, where I topped off the tank. Got great mileage from there on out. At the best of times, she gets 10-11 MPG, with the crappy CO winter fuel, if I got 6 I was lucky.
really big crew cab dually on a 1985 GMC Topkick chassis with Cat 3208, Allison auto trans, and airbrakes. 1955 GMC Scenicruiser bus, 8v-71, Allison 6 speed auto. 1966 GMC 4107 bus, 8v-71, 4 speed spicer/grinder.