Chapter 13

Gasoline

Today's gasolines are designed to burn smoothly (often referred to as antiknock quality), ignite quickly, and protect and keep the carburetor or fuel injectors clean (detergency).

The antiknock quality is determined by the gasoline's octane rating and it is important to use the correct octane for your vehicle's engine. Higher octane gasoline is more expensive so there is no point in using it if it is unnecessary.

Higher octane means greater resistance to pinging. In an older vehicle pinging may be accompanied by engine run-on or dieseling. Pinging is caused by the air/fuel mixture detonating prematurely. Your vehicle's owner's manual should specify the correct octane rating to be used, but bear in mind that this rating is generally based on a new engine.

Generally, higher octane gasoline is required for high performance engines, but sometimes other engines need the higher octane as well. If your engine develops a ping try using a higher octane gasoline. If the ping persists even with the higher octane gasoline a common cause is incorrectly set ignition timing.

Driving habits like constant stop-and-go or excessive idling may increase octane requirements because these conditions can cause buildup of combustion chamber deposits. Pulling a trailer, heavy loading, or jackrabbit starting may also contribute to higher octane needs.

If you continue to drive your vehicle that has a ping you may be causing damage to your engine's internal components, including the engine's combustion chamber, valves, rings, and pistons.

If your engine develops a knock this too may be caused by too low of an octane gasoline so try increasing the octane. However, if the knock persists some of the common causes may relate to the engine's components including a defective connecting rod or a worn piston wrist pin.