What are the implications of using different grades of gasoline in a particular car? The owner’s manual to my new Altima says that regular (87 octane) is acceptable, but what if I use a higher octane? I pay more, obviously, but what is it doing for, or to, the engine? Do diffent octane grades yield different driving performances, or would a different octanes bring about different results wrt engine life?
In general… newer cars and truck engines are designed for certain fuels. While you could put 91 octane (even though the owner’s manual states 87 is recommended), it would probably get poorer gas milege, cost a lot more, and pollute the environment more. I can’t imagine that putting the incorrect fuel into an engine would improve performance or increase the life of the engine… although it probably wouldn’t do much damage either since cars are designed to handle a at least a limited range of octane fuels…
Would you believe I was just about to start a new thread just like this one? 
I had a '76 Chevy Nova for a long time, and it required the mid-grade (89) gas, and did okay with the premium as well…but it did not like the 87 gas at all.
My folks have a '96 Olds Ciera which takes the 87 and could probably accommodate the higher grades, though they are not necessary for it.
My new used '89 Dodge Daytona can take only premium. I attempted to cheat by putting some mid-grade in it, and got the shuddery effect as a result.
If the article I read a few months ago is to be believed, you’re doing nothing but throwing away $ by buying a higher octane than your vehicle requires. It’s not supposed to improve preformance at all.
However, if your car requires a higher grade you ** must ** use that grade. Supposedly the difference in grades is that, contrary to what you’d think, higher grades have more solids in them. The reason they do is to make them burn slower(better engines=more efficent burning of fuel), which is necessary because if you use lowest grade gas in them it can, rarely bur possibly, create a fire ball in… I think it said pistons, but I could be wrong. Anyone know if this is all true?
The reason this gets so confusing is the language typically seen in the manuals. If the manual says, “Use this grade and no other”, that’s sufficiently clear; there’s no question at all. But if it says, as mine does, that the tank should be filled with “unleaded gasoline, at least 87 AKI number”, then one might assume that if you use 89 or 92, it would somehow be better.
Wrt to the environment, shame on me for not thinking of that in my original posting.
I have wondered about this since I read in car talk that octane refers the amount of anti pinging that the gas has. They say in their column that engines with higher compression need higher octane gas because it will burn prematurely causing pining. They then go on to say that higher octane pollutes more. Does anyone know why higher octane gas pollutes more?
Here are some links that talk about the original question but don’t really answer mine.
The second question for this column
The brochure mentioned in the column
http://www.ftc.gov/bcp/conline/pubs/autos/octane.htm
Ok. here’s the real deal on Octane for everyone who wants to know. The Octane number is a measure of a fuel’s tendency not to produce knock in your engine. The higher the number, the less tendency to knock. By itself, the antiknock rating (octane number) has nothing to do with fuel economy or engine efficiency. Only when an engine is designed and adjusted to take advantage of a higher-octane gasoline can the value of the fuel be obtained. Most modren engines are designed to operate efficiently with regular grade gasoline, and do not require a high-octane premium grade. So if your owner’s manual reccomends that you use 87 octane fuel, it’s best if you do that. Using anything else is not only a waste of money, but, since higher octane fuel burns hotter, it can damage your engine. If, however, you happen to have a new corvette or something that reccomends 91 octane, well you are pretty much stuck with having to pay the extra cash, since if you try to use low-grade fuel in it, your engine will probably run quite a bit worse, and also knock like crazy! I’ve had a lot of people bring their cars into my shop complaining about engine knock, and after questioning, find out that the only problem was that they were using the wrong gasoline grade! Saved them a lot of money in the long run.
So there you have it. If anyone wants to know how they go about determining a fuel’s octane rating, just ask.
Ok. here’s the real deal on Octane for everyone who wants to know. The Octane number is a measure of a fuel’s tendency not to produce knock in your engine. The higher the number, the less tendency to knock. By itself, the antiknock rating (octane number) has nothing to do with fuel economy or engine efficiency. Only when an engine is designed and adjusted to take advantage of a higher-octane gasoline can the value of the fuel be obtained. Most modren engines are designed to operate efficiently with regular grade gasoline, and do not require a high-octane premium grade. So if your owner’s manual reccomends that you use 87 octane fuel, it’s best if you do that. Using anything else is not only a waste of money, but, since higher octane fuel burns hotter, it can damage your engine. If, however, you happen to have a new corvette or something that reccomends 91 octane, well you are pretty much stuck with having to pay the extra cash, since if you try to use low-grade fuel in it, your engine will probably run quite a bit worse, and also knock like crazy! I’ve had a lot of people bring their cars into my shop complaining about engine knock, and after questioning, find out that the only problem was that they were using the wrong gasoline grade! Saved them a lot of money in the long run.
So there you have it. If anyone wants to know how they go about determining a fuel’s octane rating, just ask.
Oh, by the way, higher-octane fuel does not pollute more than normal IF it is used in an engine that is designed for it. Any other type of engine using high-octane fuel will not be able to burn it efficiently, and therefore will cause more pollution.
I should add that in my experience, my car (91 Escort, 1.9 liter engine) seems to suffer from poorer performance if I use premium octane gas instead of just plain regular unleaded. It doesn’t knock, but it doesn’t get the same acceleration or mileage, either.
catmandu42 is basically accurate. I worked in a gas station for quite a few years, and the pamphlets they gave us to read said basically what s/he said.
For more information, this page explains how they determine a fuel’s octane rating. Basically, they run it in a test engine under varying conditions and use something called, believe it or don’t, a “knockmeter” see how much knock there is. Sounds primitive, but hey, I guess it must work. On the other hand, this page tells you why they use the numbers 87, 89, etc. (I seem to remember Sunoco came out with a 94-octane gasoline at one point…do they still make it?)
From my memory of the halcyon gas-pumping days of my youth, I seem to recall that, if your car runs fine on regular fuel, the biggest benefit of using a higher-octane fuel is found in the pockets of the station owners and oil companies; the markups on the higher grades tend to be larger.
Just FYI, did you know that Diesel fuel has something similar? It’s called a Cetane rating, and it goes from around 30 to 100. Instead of anti-knock, however, Cetane ratings measure the ignition lag time (delay time) from the point in which the fuel enters the combustion chamber until it ignites. The higher the number, the shorter the lag time. Good to know if you have a diesel engine, because depending on your RPM’s, certain deisels CANNOT run on too low of a cetane-numbered fuel.
Once in a while I’ll see regular for $1.50, mid-grade for $1.60, but premium is only $1.61. Do they just have too much premium and they’re trying to get rid of it, by encouraging mid-grade buyers to spend another penny, even though there’s no real benefit?