I think that is the start of the modification of the blend, but it is changed also a month or two later. Summer blends start around March? It depends upon where in the country you are too.

1. You might check with your Amsoil dealer. https://www.amsoil.com/products/promo...aranteeWeb.pdf
Their P.I. gas treatment guarantees MPG improvement.
Worth a try, don't you think?

2. I get my gas from Costco because it costs less. Here they get it from; Tosoro, Shell, Chevron, Unocal and Exxon. Whichever is cheaper. It all has the Costco additive package when it goes into the truck. Gasoline that comes out of the refinery is essentially the same.
So, I suggest you fill at a high volume station so you are getting fresh fuel, and pay the lowest cost you can find.

3. And, sometimes you may experience a drop in MPG. This may be because the refinery made too much high octaine and sold it as regular to the station to get rid of it. Putting higher octaine than recommended in your tank reduces MPG.

I don't think I've ever heard of that. Can you explain it more?

I've heard that before, but I don't think I've ever seen any data to back it up. Personally I feel that all things being equal (Ethanol content, additives, etc) the difference in mileage would be statistically insignificant.

-Jay

Fiat 1500 Station Wagon, Chrysler 300, Volvo DL, Honda Accord, Pontiac LeMans, GMC Sonoma, Dodge Dakota, Honda Prelude.
Simple 4-Banger to sophostocated 4-Cylinder, Original Hemi to....well, I havn't done it with the new Tundra.

At least one full tank of gas on I-5 between San Francisco and Los Angeles or between Los Angeles and San Francisco.
"The Grapevine" is the mountain pass between the LA Basin and the Central Valley and the rise is to 4,000 feet or so, the rest of the trip is nearly sea level.

Dividing miled drove by gallons consumed, gas mileage has always gone down using higher octane than recommended.

Any guesses why? As I said, I don't recall ever hearing of anybody else who observed that data, but it's interesting if true. It behooves us to find out why; this is the sort of thing that eventually leads to a new strategy, modification, or idea, once we learn the concepts behind the observation.

A first simple guess would be that the additives required to raise the octane dilute the gas, but I doubt that the percentage of additive is enough for that.

Simply; The engine is tuned for the lower octane gas.

That doesn't tell me anything about why it gets lower FE on high octane gas.

What does that mean, besides compression ratio / timing?

What is it about higher octane rated gas that makes it produce less power in an engine optimized for lower octane ratings?

this is the explination that I heard, is it true? I don't know.

with higher octane gas, the engine must advance the timing. depending on your engine, your ECU may only be able to advance the timing so far or if you are carburated, you have to adjust the timing. I assume they are talking about the spark plug fire. most modern engines do this automatically and I can't see where it would be an issue.

do I have data to back this up? no

I was having issues with my riding mower and I was asked what kind of gas I put in it. I usually just fill the container when I fill my car and yes I usually put premium in my car. I have been putting regular in it lately because stations around here still don't have premium. they are starting to get midgrade back in stock.

this was just a "for what it's worth" statement. take it for what it is. just something someone told me. true? false? I don't know.

My dad always used premium in his lawnmower and tractor because they were initially built for leaded gasoline. His logic being that regular leaded gasoline had higher octane than your standard 87 octane does now.