The Car and Truck Fleet and Leasing Management Magazine

Which Fuel Grade is Best for Your Fleet Vehicle?

When it’s time to fuel up your vehicle, is premium fuel ever worth the extra cost? Here are a few tips to help make a decision.

January 2009, by J.J. Keig

Why do some vehicles run better and have fewer problems than others? Could it be as simple as the gasoline purchased? Many people believe premium or high octane fuel is good for their cars and burning it every now and then is good to “clean things out.” Unfortunately, the only thing that will be cleaned out are funds in fuel purchase.

The only benefit high octane gasoline offers is resistance to pre-ignition or knock, which the octane value indicates. Octane has nothing to do with gasoline’s cleanliness or potency.

Just What is in Gasoline?

Gasoline comprises different oil base stocks. After the refining process removes undesirable components, additives and detergents are blended with the remaining fuel to achieve a unique recipe or blend. Each blend reflects a complex balance of chemicals that may be seasonally adjusted to aid desired performance in certain temperatures and provide varying degrees of cleansing or detergent agents. Of particular issue is the nature and amount of additives that comprise a detergent package.

Measuring and controlling gasoline in the fuel delivery system is critical to an engine’s overall performance and efficiency. In modern engines, fuel can be measured and regulated precisely to control any variable or factor in the fuel or its production. A tank of gasoline with minimal detergents and other additives is prone to form gums, varnishes, and other properties that promote coking and deposits.

These undesirable properties, even in very small amounts, not only inhibit fuel performance, but also precipitate harmful conditions inside the motor itself, leading to poor vehicle performance and drivability, reduced fuel mileage, and significantly increased emissions. Specific damages include carbon build-up, sticking valves, gumming, varnishing, reduced spray patterns, dribbling, engine hesitation, stumbling, rough idle, and overall poor performance.

Selecting a Fuel Grade

When selecting a fuel grade, be sure to follow the vehicle’s owner’s manual and/or instructions on the fuel gauge. If no special fuel is indicated, the lowest octane fuel available may be purchased safely. If, on the other hand, mid-range or high octane is indicated, those instructions should be followed.

Virtually all engines manufactured during the past 15 years have incorporated knock sensors that assist the vehicle computer in optimizing engine controls, thus maximizing economy and performance. Regardless of the gasoline grade used, the engine manages input values and makes adjustments many times per second, controlling the tendency to knock before it even happens. Thus, if not designed to operate on mid-range or premium fuel, a vehicle achieves no benefit from its use, and the cost of extra octane goes right out the tailpipe.

Fuel quality can be measured in another, more meaningful way via the additive package, especially the detergents added to base stocks at distribution terminals. Different gasolines in a specific market area, in fact, may be drawn from one, two, or a small number of distribution terminals. In most instances at a final bulk transfer point, special additive packages are blended with the fuel. That particular supply of fuel achieves a specific profile or recipe as prescribed by the oil or fuel company designating it as its brand.

Many companies promote the detergent aspect of their gasoline products, a factor that plays a vital role in the health and well being of any gasoline engine.

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