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How to Purchase the Right Gasoline

Different brands of gas--even those with the same octane rating-- can cause a vehicle to behave very differently. Your car may act sluggish or misfire (knock) on one oil company's fuel but not another's. Since different refineries offer different formulations of oxygenates, detergents and even octanes, changing brands will often perk up sluggish performance.

Overall Things You'll Need

• Owner's manual

Steps:

1. Check your car's owner manual for the recommended fuel (unleaded gasoline versus diesel) and octane rating or antiknock index (on the yellow sticker affixed to the pump).
2. Try another gasoline brand if your car isn't running smoothly on the manufacturer's required minimum octane. Each refinery mixes its own blends with additives to encourage cleaner burning. Your car may simply need a higher-quality fuel with more scrubbing power to clean out its fuel system and run better. If switching fuels doesn't solve the problem, it may be time to have your mechanic search for a different cause.
3. Get the skinny on octane numbers. Octane ratings are based on a scale of relative burn resistance: Higher-octane gas will not combust prematurely and cause your engine to knock.
4. If your vehicle makes a knocking sound on acceleration, try a higher-octane gasoline. Most cars can optimize their own performance to the gas they're fed, but only up to a certain point: Gas with too low an antiknock index causes an engine to fire prematurely and lose power. Gas with an antiknock index well above the required octane level doesn't increase performance or power, just your fuel costs.
5. Try changing brands again if your engine runs rougher in winter, since fuel blends change seasonally.

What To Look For

• Manufacturer's fuel recommendation
• Octane rating
• No knocking sound
• Improved engine power

Overall Tips & Warnings

• If your car is running smoothly and getting top gas mileage, there's no need to use a higher-octane fuel.
• Engine knock is very damaging to cars. Simply increasing the octane level can save your car from expensive engine wear and tear.
• MTBE is an oxygenate added to fuel to increase its octane rating and clean up emissions. It has proven to be an environmental disaster, leaking into the groundwater supply. As of 2000, the EPA is reducing the use of MTBE.

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