Check Your Vehicle's Gas Mileage and Octane Requirements
Checking your vehicle's gas Increase-Fuel-Mileage-on-a-Car is pretty easy, and you can determine it's octane requirements as it ages using the same method, detailed in the steps below.
Steps
- Fill up the gas tank. It isn't a good idea to "top off" your tank nowadays, apparently; but if you do, just stay consistent and top off later, when refilling, also.
- Reset your trip odometer. If you don't have a trip odometer, write down the mileage.
- Drive around. You should always drive on the "top half" of your tank, especially for newer cars; but let your tank get down to at least half full.
- Fill up the gas tank (using the next higher octane from last time, if you want to check the octane requirements of your vehicle). Check odometer, or do the math, to determine how many miles you've driven since the last fill-up; divide by the number of gallons you just filled up with, for example: {{safesubst:#invoke:convert|convert}}/{{safesubst:#invoke:convert|convert}} = 20 mpg.
- Octane is a pre-explosion inhibitor, and older vehicles tend to require more octane for best performance and gas mileage due to carbon buildup raising the compression ratio. Newer vehicles may often benefit from higher octane as well, depending upon their computer settings; but it is pointless to get higher octane gas than your vehicle can use.
To Check for Octane Requirements
- Reset the trip odometer, or jot down the new odometer reading.
- Drive down to a half tank again.
- Fill up the tank. If you've noticed considerably better mileage, refill with the higher octane; if not, use the lower (this puts the cart before the horse, this time; but you have to fill up to calculate mpg).
- Divide mileage/gallons to get mpg for higher octane. In this example, we'll say {{safesubst:#invoke:convert|convert}}/{{safesubst:#invoke:convert|convert}} = 24 mpg.
- Divide the increase in gas mileage by the mpg at the lower octane rating to get increased mpg in %. Example: mpg @ higher octane = 24 mpg, for an increase of 4 mpg; mpg @ lower octane = 20 mpg; 4/20 = .20, or a 20% increase in mpg @ higher octane. Woo-hoo! As a rule of thumb, you should use the higher octane if you get a 3-5% or more improvement in mpg, strictly on a cost basis- but personal considerations may sway this (at $3 a gallon v. $3.10 a gallon = 3.3%). At about a 10% improvement, more or less, you should notice smoother running, also.
- You only have a half a tank of higher octane gas, if you refilled at a half tank, so this should be taken into consideration. A tank full of 87 octane, driven down to a half a tank, and refilled with 91 octane, would give you a tank of roughly 89 octane gas.
Tips
- You can also compare the "same" octanes of different gas stations this way- with sometimes surprising results.
- Your cell phone has a calculator for precise division.
