Anyone wishing to opine? I'm now getting 10% less mileage than a month ago - will changing to higher octane gas help / hurt in this instance (winter gas).
No one has demonstrated that any Prius (2001 to 2010) ever gets better (or even as good as 87) gas mileage on any Premium gas. There is plenty of evidence that the older Prius react particularly badly to both winter blend gas and E10 gas. They also react badly to colder temperatures. http://www.theoildrum.com/story/2006/9/13/234043/431 http://en.wikipedia.org/wiki/Ethanol_fuel#Fuel_economy http://hiwaay.net/~bzwilson/prius/pri_mpg_temp_010.jpg Since no one has driven a 2010 through a winter yet, you get to be our guinea pig on how it does.
Without having seen tests on this subject I would guess you would get worse MPG with higher octane fuel. Higher octane fuel is more resistant to burning. You are working with cooler temps which makes the engine take longer and work harder to maintain optimum operating temperature. Higher octane fuel would not help you in this scenario because you should not be experiencing any knock or detonation because of the cooler temps and thus you are already working within optimum parameters (with regards to timing and fuel maps). In very hot ambient temperatures and high load situations you may benefit from higher octane because you have a greater risk of experiencing a pre-ignition or detonation situation. Your car's computer would then retard timing and you would lose power and efficiency. Higher octane is less likely to burn uncontrollably and thus resists detonation. Gasoline FAQ - Part 1 of 4
I too am finding lower mileage on my G3, IV (7200 miles) here in Utah now that cold wintry weather has arrived. I am sure the winter gas blend is a major factor, however, so much depend on your driving environment. When it was 15-20 degrees recently, the ICE would run most of the time, especially on short trips. Naturally, the mileage was way down. Then I experimented and purposely took a longer drive, making every effort to drive non-stop at 35-45 mph for a number of miles. The mileage responded, and the mpg average climed to slightly less than the Summer average. In Winter, air contracts, so I need to check my tire pressure ... I bet it is lower than the recommended pressure. Lastly, driving through snow and slush has to be causing more drag and rolling resistance. I am confident the mileage will be back up come Spring and Summer. Remember, all these issues impact every car. My last car was an Acura RSX, and it's Winter mileage was significantly lower in the Winter also.
There is a warning in the Tech literature against using higher octane fuel. I have posted it before: http://priuschat.com/forums/gen-ii-...0-fuel-economy-vs-grade-brand.html#post718580
Most people don't rev or hit the gas hard enough to get near detonation, just look at how many people cry about losing 1mpg
In my town, only two stations sell 87 octane regular gasoline, the rest sell 85 octane as regular. This is true year-round. Check the pump each time you fill up.
The battery won't work as well in cold weather as the low temps slow down the chemical reaction that produces electricity. The coupled with the higher load on the cabin heater means the IC has to run more often and for longer.
high octane gas will only increase your fuel bill. it probably has a detrimental effect in winter since the only real reason any one uses high octane fuel is to prevent early detonation. any fuel/air mixture has a flash point. that is the temp at which it will explode without need of the spark. its obvious that if this happens at the wrong time, the momentum from the explosion could actually work against your engine. now, in summer, your engine runs hotter so the potential to hit the flashpoint is higher, intake air is warmer, etc. the other thing is that the higher the compression ratio, the hotter the mixture gets... ya know, conservation of energy, same amount of heat but in a smaller area creates higher temp and so on... so, contrary to popular belief, high octane gas does not have more energy and frankly, does not burn as well, and thrives in hot running engines all of which is detrimental you what you want, especially at this time of year... unless of course your name is Pat Sparks!!
True, true. He is usually full of hot air and I almost had to pour high octane fuel into him to reduce the chance of detonation when he was replying to people in the global warming threads.
