Brand of gas determine MPG?

I've never seen anything like this.

I just came back from a several hundred mile trip almost all on the interstate. I had been averaging 18 MPG since I bought the truck, and on the first two tanks of the trip got 20.5 and 19.9 - appropriate.

Then I filled up, at a IL Shell station and got a miserable 16.9 - my worst tank ever. Then the last fill up got back to 18.

This was all within a couple days time, and yes there were a few miles of non-interstate on that Shell gas.

So what the hey? Why would one tank of gas get such bad mileage?

 

Boy beats me, I buy gas at all kinds of places, usually get 18ish in town and around 22 on the road. That's kind of strange.

 

The quality of gas will absolutely affect your mileage. Zero doubt.

I'm a chemist. I know. Seriously.

 

... and ... here is a nice little site. Don't know how true this is, but at least it's a start ... http://www.toptiergas.com/

 

there are soooo many factors though... a small headwind will kill mpg.... 10mph head wind takes your wind speed at 65mph indicated by the speedo to a technical 75mph that the truck has to push through..... i can pull 23mpg at 65 mph.... 75 drops that to 17mpg.

 

I usually buy gas at whatever station is cheapest, Raceway, Speedway, or Midnight Oil in this area, but the "offending" gas was from Shell - what I'd normally consider a "good gasoline"

 

Well, maybe, but that doesn't explain the fill up after that tank. I was still going in the same direction.


On the other hand - would there be any STATE differences in formulations? That was the only tank I bought in IL, the others were in TN. ???

 

Illinois gas probably contains 10% ethanol, which will reduce mileage. Does your Tennessee gas contain ethanol?

Ethanol-free gasoline is virtually unavailable in Ohio. I can buy 91 octane ethanol-free gas, but at $4.56 a gallon. It is popular as a fuel for small engines. Corn belt states tend to have ethanol in their gasoline.

 

Yes, TN does have many stations with 100% gas, but its about $0.30/gallon more expensive. And, yes, your vehicle will get *slightly* better mileage on it... but I don't buy it. (I've run the numbers and the increased mileage does not make up for the increased cost)

 

I see no difference buy gas all over the place in the North East it's all 10% ethanol. If you stop when the fill clicks off you still can get a gallon or more in the tank so that may explain your difference.

 

I have UltraGauge monitoring instantaneous and average MPG, I saw the difference there before I even filled up.


"I see no difference" - ya I know, I've been buying gas for a long time now... but that's even more reason why I thought it was crazy that this one tank would be so bad.

 

I have used nothing but Sunoco since new and have a consistent 17.7 - 18.3 MPG

 

Funny thing is that there is a shell station near me. I was getting horrible mileage and pinging with gas from that station. Started going to a different station and it was a huge improvement. One day I was driving by and noticed a tanker truck refilling the station. It was old and messed up truck without shell logo. I was going to report that station to shell corporate but lost interest. Maybe we live in same hood? lol

 

Too many variables. Someone already mentioned 'headwinds'. You could also be traveling uphill....vs coasting downhill. Different gases with different amounts of ethanol.

Plus - I don't know how far away you were traveling, but its that time of year where gas is being converted over to 'winter' gas mixtures. Perhaps the one gas station was still running summer mixture while the other gas station had already converted over to winter gas. Just a guess....

Every year, I see a pretty dramatic change between winter & summer gas mixtures. My truck doesn't like the winter gas/winter at all. I'll lose about 2mpg every time it switches over from summer to winter fuel. And that's my regular day to day driving and over the last 7+ years of owning my truck.

 

I always go to quik trip to get my gas.... 17.x combined, 18.x highway, 16.x with mostly city....

 

I use what ever is near by when I fill up and get a pretty consistent 20 MPG with a 6 speed. My UltraGauge is all ways off on a fill up by about a gallon but fairly close on total MPG. against a calculator. An 18% drop is a significant difference far more than just brands, gasoline all comes from the same place and what they do to it afterwords can't make that much difference.

 

There is a local trucker here in town he has C.N. Brown stickers on his truck (a local fuel Co.) I also have seen him hauling water for Poland Springs (not the same tanker) neither of the tankers are labeled. It's not unusual for an independent to haul fuel for a major brand. Maybe the OP got a tank of Poland Spring water.

 

I see a difference between ethanol and non-ethanol gas but the non-ethanol is so expensive here (need to go to specialty gas stations) it's not worth it.

No difference between regular brands though such as costco vs shell vs valero or whatnot.

 

Years ago I had a wooden boat with a 40hp 2 cycle engine. My friends and I used to ski and we were always scrounging money for gas. The boat would do about 27 MPH max with a single ski skier behind. This is a different set up from out vehicles as it has only one gear in forward and the engine must be able to run for hours at full throttle and also idle on a gas/oil mix.

I had mostly used an old Gulf station on one side of town - but I changed to a Mobil a few times. The Effect was immediate and dramatic - Ran poor and cut out a little at idle - but top speed lost almost 10 MPG with the same skiers behind the boat. I thought I had engine troubles and it was so slow it was barely skiable. When I switch back - to the other station there was an immediate fix.

 

I get about 1 mpg more using Shell or Chevron vs. the local grocery store gas.