premium gas in a regular car
 

I mistakenly filled my car with high octane gasoline. my mileage which has been mid 30s, jumped to low 40s . can premium gas do this? will it hurt my car?

Perhaps you should see if that's a repeatable result. No harm will come from it though.

My Subaru would only run well on high test until I reset the timing.sc

It will not hurt anything at all.
This kind of increase is sometimes blamed in the anti-knock properties of higher octane gasoline and it's sometimes credited with premium gas not having ethanol in it, either way if your car really does get improved mileage from higher grade gasoline it can be well worth the extra 10 or 20 cents per gallon because your cost per mile is dropping.

if the results are repeatable, I pay 54 dollars to fill with regular 58 to fill with premium and it would cost 64 dollars to travel the same distance on regular as I am able to on premium.

my wife filled the tank though and brought me the receipt and mileage so I am not really holding my breath on it!

http://ecomodder.com/forum/fe-graphs/graph5973.gif

Which tank was filled with premium? The last two tank average is 33.985. Fill error? As Frank said repeatable? I also see forties once before how was that achieved?

I did a fuel cleaning with seafoam and drove the car like it was a rental. that is why the mileage is around 26 mpg. the 40mpg previously was with a huge grill block that hung down like an airdam and a small upper grill block, smooth wheel covers, and a recent professional alignment . I removed the huge air dam because I think the transmission overheated. The wheels were also very bald, and since then I have put on new tires that have actual tread on them.

I would suspect that a number of other factors influenced the high mileage of this particular tank--prevailing winds and travel direction, temperatures, number of acceleration/deceleration events, rate of acceleration events, average speed--any number of things. You can't chalk it up to the premium right off the bat without controlling for other variables. Here's what Cartalk has to say:

"Premium gas gives you more miles per gallon than regular gas.

Sorry, that's pretty much booo-gus.

Here's why.

Each gallon of gas that we pump from our local Quickie Mart is actually made up from as many as seven different ingredients. The exact amount of energy in each gallon of premium or regular gas will vary from company to company, depending upon what kind of additives they use.

In actual fact, you'll get a greater range of fuel economy between different brands of regular gas, than you will between the same manufacturer's regular and premium gasses. Interesting, eh? We thought so.

Finally, here's a nice irony: to increase gas' octane rating, companies add ethanol, when they're mixing up a batch of premium fuel. Interestingly, ethanol actually contains less energy than untreated gas, so the net result from the ethanol component is a reduction in your MPG. Other premium additives, however, have the reverse effect, and slightly increase your MPG. So okay, overall premium provides a very slight net increase in MPG, but it's so slight that we swear you won't notice the difference.

I always used the increased MPG that resulted from using premium as a justification to purchase it.

Too bad. Consider yourself better informed now, and stop lining the pockets of oil companies, okay?"

H
ere is something strange about the gas companies in Nova Scotia. Many companies sell pure gas if you buy the 91 octane. the 87 and 89 are E 10 gasolines! This might be my answer.

That is how it is here as well, the lower grades of gasoline have ethanol in them while the premium does not, so the lower grades have less energy in them and if your engine has a knock then the most common way to make that knock go away is by adding more fuel for the cooling effects and because an engine that is running lean tends to run hotter.