Is it actually worthwhile to buy 93 octane gas? Or should I save myself the 10-20 cents/gallon and just buy 89? I drive a 93 Toyota Camry LE, 4 cylinders, and the owner’s manual says to get the more expensive gas, but I’m not sure why.
Why is there no 91 octane gas? At every gas station I’ve ever seen, the octane jumps from 89 to 93 for no discernable reason.
Why would my car get 300 miles to a tank city and almost 400 highway? Is this an unusually large disparity in city v. highway mileage?
I am very curious about this stuff and have a basic working knowledge about cars, though I’m largely in the dark about these things.
City mileage is less than highway mileage because there is more stopping and starting involved (stoplights, stop signs, heavy traffic, etc). Acceleration to a particular speed requires more fuel than maintaining that speed. 3-5 mpg would be a standard disparity, but I don’t know how many gallons a tank of gas is for you and moreover I am too lazy to try to do math to find out whether yours fits it or not.
I’d say my gas tank holds about 16 gallons (I could be wrong). If the disparity is 5 mpg, mine is still big. I was able to drive from Binghamton, NY to Richmond, VA on 1 tank of gas, but can barely make it through a week of local driving to and from work. I find this weird. I realize that it’s only 25 miles to the gallon highway, so that part isn’t so off, but to get only 18 or so city seems low for a Camry. Yes, I have it serviced regularly, though all of a sudden it won’t go in reverse–time for a new tranny, I suspect.
No, higher octane than required MAY improve performance but no guarantee on that. It will probably not improve gas mileage. Actually, your 10 year old car, if it’s got a lot of miles, may have lost enough compression that it can’t effectively use high octane anymore.
Some places do have 91 octane as a “mid-grade” fuel, but it’s not one of the standards. Actually, you can blend gas to any octane you want, if there’s a market for it. I think it was Sunoco that used to have pumps that would blend to any of about 6 or 7 different octanes, each at it’s own price.
Gas mileage is so affected by individual driving, you can’t predict it.
So I should just buy the 89 octane from now on? This will save me plenty of $$$ in the long run.
KenGr: Are you saying that there is scientifically something about the way I drive that makes my car so much more efficient on the highway than in the city? Is there a way to drive that will be more fuel efficient?
If you want max fuel efficiency, keep a few things in mind:
a) Cars burn gas at their highest level under acceleration.
b) If you’re going a few blocks with traffic lights, approach every light slowly so you’re less likely to get stuck at a red one. If you’re going a few blocks with stop signs, don’t drop the hammer and drag race to the stop sign.
c) Coast as much as possible.
d) If you have to put considerable pressure on the brake pedal when you stop, you’re wasting gas, as all you’re doing is reducing speed generated under acceleration, which as I said is a fuel mileage killer.
You can coax some mad miles out of your car if you want to, but you’ll be driving in a manner inconsistent with most everyone else, so you’ll have to be very careful of people who will cut you off or tailgate you because you’re going too slow.
Incidentally, here’s a good description of why you need higher-octane-rated gas for some engines.
My mother actually tested this with her toyota camry (also a 93, I think). It got the best mileage with 89 octane. I wasn’t surprised that the 87 got worse mileage, but I was suprised that the 91 octane mileage was slightly worse than the 89 (but not as bad as the 87). This was driving the same road to work and back during the week, which was mostly interstate driving, about 20 miles one way.
If your owner’s manual says to use 93 octane gasoline as a minimum, then I’d keep using it. Unless the engine management system is equipped with a knock sensor to advance or retard the ignition, it is entirely possible that the engine can be damaged if you use lesser grades. Sometimes the owner’s manual for knock sensor-equipped cars will state something like “Premium unleaded (min 93) is recommended. NEVER use less than 87 octane”, which means that you can use 87 but might take a hit on performance and/or mileage.
I can’t recall ever seeing 91 around my area, so I can’t help here.
Your highway vs. city mileage doesn’t sound that far off. Let’s assume each fill-up for you takes about 14 gallons. One week you do 300 miles in the city. That’s about 22 mpg. The next week you do 400 miles on the highway. Thats almost 29 mpg. Sounds normal to me. I get about 22 city and 31 highway. As KenGr points out, your highway speed does affect mileage too, though I’ve found that I get my best highway mileage well above 55mph (not that I condone that for anyone else).
91 octane petrol is highly common in Kansas City. 93 is somewhat uncommon, in fact. I imagine it may vary regionally a bit depending upon the level of oxygenates in the fuel and the level of volatility/additives for volatility control.
I grew up in West Virginia, now live in Ohio, and in both places 87/89/93 octane was standard. However, some gas stations around here do 87/89/92, and the Sunocos all have 86/87/89/93/94 (Economy, Regular, Plus, Super, Ultra 94).
But in western Pennsylvania, you’d be hard pressed to find anything but 87/89/91. I’ve seen 91-octane as the highest grade in lots of places I’ve traveled.
Two of my cars require 91-octane minimum, and any gas station you find will be able to accomodate that.
Why? Because the design of the engine requires the higher octane to avoid preignition and the damage it can cause. The money you save on gas will only pay for a portion of repairing the engine damage caused by using a lower octane than required.
Acceleration, as racinchikki said, is not fuel efficient. Braking takes kenetic energy that you burned gas to get and turns it into heat, so that fuel is basically thrown away. Your engine is least efficient when it is cold, better when warmed up. So, stop-and-go driving for short distance gives you lousy mileage.
Finally, air resistance hurts your mileage, so driving 80 instead of 55 on the highway will affect your fuel consumption.
I’ve always been advised to use the lowest octane gas you can that allows the car to run properly. If you have problems with preignition (described as “knocking and pinging,” IIRC) on the cheapest grade of gas, go up a notch, or until the problems stop.
I’d agree with this (you may also start on high octane, and drop until it pings, then go back up). Or simply consult your owner’s manual and believe it. I have a car whose manual says it requires 91 octane, and have no particular urge to find out if 89 will make it ping or not.
People get confused about the meaning of octane ratings, partially because it’s the higher compression “performance” engines that require the high octane. This leads people to believe that they are going to get an extra boost from putting the high octane gas, and have the engine in their Taurus crank out the horses to turn it into a race car. That’s backwards. Higher octane fuels burn SLOWER, and are formulated expressly to prevent preignition in higher compression engines, not to produce any more “power”. The higher compression engine design is what produces the extra power.
As usual, we can partially blame advertising - they always label the high octane pump “Performance Plus”, or something like this, and don’t emphasize that it’s “gas for high performance engines”, not “gas that will give your engine high performance”.
I agree with yabob. I just want to add that my car’s manual suggests 91 octane gas. Locally, it’s only available at a few Sunoco stations. I was assured at the dealership that it would run fine on the much more common 89 octane gas, and I haven’t experienced any problems with knocking.
One other point… it’s not really true that accelleration is when you get the worst gas milage. That’s second worst.
Worst is waiting in traffic or a light, not moving at all but burning gas.
Miles per gallon = 0.
If you do a lot of this it can account for any level of terrible city milage.
Question: I’ve always understood that 87 Octane gasoline means 87% Octane Hyrdrocarbons (which compress very well) and 13% other variations on hyrdocarbons (which don’t compress very well). And if you were using 93 Octane, it meant 93% Octane Hydrocarbons and just 7% Other.
So how do you get 115 Octane AVGAS - as used in Spitfires and P51 Mustangs and other super-high-performance Aviation gasoline engines?
You’re understanding is correct as far as the original definition of octane, but it goes further. Antiknock additives such as tetraethyl lead can be added to fuel to reduce its propensity for preignition.
