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I am seeing a 3-4mpg drop in fuel economy recently. It started around mid/late september. I can't seem to get back to 30 mpg no matter how hard I try. The car is running perfect, so I am not sure what is going on. Could it be that the winter gas has come out now at the gas stations?
I believe all the gas stations around my house are using E10, so I don't think it is that. I did fill up at a Speedway when I first noticed the problem, but I have since then filled up at my normal Miejer gas station and noticed the same drop in FE.

I found the same thing. and I live in a much warmer state.

How have temperatures been in your areas? Colder weather usually brings lower FE.

How have temperatures been in your areas? Colder weather usually brings lower FE.

and softer tires. You should recheck your PSI.

...Could it be that the winter gas has come out now at the gas stations? ...

The fuel blends change in multiple steps between summer and winter. But my oil industry relative hasn't worked in the blending unit for a long time, so I can't give you any dates. The EPA website should have it -- somewhere, if anyone has any clue where to look.

Hi Tommyt31:

___This question gets asked every fall and spring and I should have it bookmarked :( IIRC, the mandated Winter/Summer RFG switchover dates are Oct. 15 and May 1 with the blending beginning about a month before so the refiners tanks and than the gas stations tanks can meet the deadline with a given percentage.

___That being said, 3 to 4 mpg has everything to do with temperature acting on your vehicle AND fuel. Increased RRc’s, aero and mechanical drag, longer period for warm up and less energy carrying fuel are all contributors :(

___Good Luck

___Wayne

the mandated Winter/Summer RFG switchover dates are Oct. 15 and May 1 with the blending beginning about a month before so the refiners tanks and than the gas stations tanks can meet the deadline with a given percentage.

Why don't you add it to Beating the EPA. That way everyone reads it. :)

AAAAAAHH!!! It all makes sense. May 2nd: 35MPG, May 11th: 38. October 9th: 38 MPG, October 27th: 36.

I read an article today about winter fuel in Canada. Winter gasoline blends start in mid September, and the "full" winter gasoline must be available by November 1. Reduced winter blends start coming back between March and April, and full summer gasoline starts arriving around mid May.

My car missed the summer gas! March 28 tank lasted until Dec. 6 (why did I take off the snow tires?). I think one of the biggest problems with winter hypermiling is short daylight hours and the extra battery drain when FASing with headlights on. BTW, my car's ICE runs fine despite sitting unused most of the summer, but next summer I will be hooking up a battery charger regularly. I had to tell my wife not to turn my car off at stoplights when she borrowed it on a snow day last week, because the battery was having troubles.

Maybe I'm just dumb - but could someone please explain to me WHY the gas formulation changes? What is the rationale for it?

Maybe I'm just dumb - but could someone please explain to me WHY the gas formulation changes? What is the rationale for it?

Basically gas vaporizes very poorly at very cold temperatures. This means it's hard for cars to start in the winter and to keep running until they warm up. The winter formulation is designed to vaporize more easily, allowing easier starts and better running on those extremely cold days.

Clearly there are some places that don't need the winter formulation however. Here in Las Cruces the absolute low in the nights is freezing or a few degrees above. We had one day where it got down to 20 F at night and that was the very coldest night of the whole winter.

Maybe I'm just dumb - but could someone please explain to me WHY the gas formulation changes? What is the rationale for it?

Basically gas vaporizes very poorly at very cold temperatures. This means it's hard for cars to start in the winter and to keep running until they warm up. The winter formulation is designed to vaporize more easily, allowing easier starts and better running on those extremely cold days. ...

In the other direction, winter gas vaporizes too easily in summer, causing vapor lock, and excessive evaporated hydrocarbons that contribute to local air pollution.

Has anyone thought of "stocking up" on summer gas to see the actual loss of economy from winter gas.

Thought about it but never had the resources to do so.

I sort of did by running my summer tank into winter, but I don't really have a comparison to make because I've not driven the car recently, or at the same temperatures.