Has anyone noticed this as well?

It's usually the other way around winter gas (oxygenated) has less power than summer gas (Courtesy of Chevron):


The oxygenated gasoline season begins October 1 or November 1, depending on the area. This coincides with changes in the weather -- lower temperatures and rain or snow -- which reduce fuel economy.

Summer or winter, a car's fuel economy is lower while it is warming up, a process that takes 5 to 10 miles or urban driving. Factors which make the effect greater when temperatures are lower include: more time spent at idle to defog/defrost windows of cars parked outside, more time spent using a "fuel rich" warm up mixture, and the additional energy needed to overcome higher viscosities of the cold fluids: engine oil, differential oil, and transmission fluid. The effect is magnified by short trips. The fuel economy of a five mile trip can be 5% to 15% lower in winter.4
One might assume that the energy saved by not running the car's air conditioner would counter-balance some of the low temperature warm up effects. But the air conditioners of many cars operate when the climate controls are on the "defrost" or "defog" setting to improve defogging performance by reducing the humidity of air blown on the windshield.
Rain or snow on the roadway decreases fuel economy because it offers more resistance to the forward motion of the tires. Loss of traction (tire spinning) also decreases fuel economy.
Finally, bad weather often results in more bumper-to-bumper travel during commute times. Stop and go driving exacts a heavy fuel economy penalty.

Adjusting gasoline volatility for seasonal ambient temperatures also requires changes in gasoline composition. Summer gasoline is given a lower volatility to avoid vapor lock and minimize evaporative losses. Winter gasoline (both conventional and oxygenated) is given a higher volatility to facilitate starting and warmup. The compositional changes required for the shift from summer gasoline to winter gasoline decrease the gasoline's energy content. Depending on the magnitude of the volatility change, the fuel economy of winter gasoline will be 0.5% to 1.5% lower than of summer gasoline.

 

I also found out that in the US, there is a bi-product of gasoline that is hightly toxic and the major gas companies have tons and tons of it so what do they do with it? In the winter time since you are supposed to get the best gas mileage, they put a percentage in each gallon of gasoline so that you really do not notice much difference in the MPG; and the best part, it is perfectly legal. I laughed and did not believe it when I first heard it but it acutally turned out to be true. One of those things that they do not want you to know.

 

Is your AC on? That kills some of the power, atleast in my car it does.

 

If you buy gas from the same station you always do try and switch to another brand or to another station and see if the same thing seems to occur. Some gas stations mix gas when they get deliveries of too much regular gas and what they do is they tip it over into the premium tanks so they do not have to take it back to the gas depot.

 

I gased my SUV at a place called Jersey Oil...boy did I notice a significant difference aft. (not positive of course)

 

Wow. Watching this thread, I am learning a lot about gas stations. Kinda makes you not want to go to them or at least have your own.

 

I monitor my MPG on both my cars. I haven't seen a significant performance decrease in either car.

However


It does seem the daily beater is a bit less responsive on the throttle lately. The 308? Heck, it only knows idle & to-the-metal, so it's not a fair test