How to Buy the Right Spark Plugs

1 of 6 in Series: The Essentials of Replacing and Gapping Spark Plugs

To buy the proper spark plugs for your vehicle, you must know its specifications. Your owner’s manual may have specifications for buying and gapping the spark plugs on your vehicle. If you don’t have an owner’s manual, or if yours lacks the necessary information, you can find the correct spark plugs and spark plug gap in a general “Tune-Up Specification Guide” (called a “spec sheet,” for short) at an auto supply store. These guides are either in pamphlet form or printed on large sheets, like the one shown here, that are displayed near the parts section of the store.

Use ignition specifications to find the right plugs. These specs are for a 2004 Toyota Prius.
Use ignition specifications to find the right plugs. These specs are for a 2004 Toyota Prius.

To obtain the specs for your particular vehicle, you need some basic information. All this information should be in your owner’s manual, and most of it is also printed on metal tags or decals located inside your hood. You can usually find these in front of the radiator, inside the fenders, inside the hood, or maybe even inside the lid of the glove compartment. These identification tags also provide a lot of other information about where the vehicle was made, what kind of paint it has, and so on, but don’t worry about that information right now.

At the auto supply store, don’t just ask a salesperson which type of plug you should buy — you have a very good chance of getting the wrong one. First look up the specifications yourself, and then ask for the plug by number. If you’re unsure, have a salesperson double-check it for you.

Here’s what you need to know to obtain the specs for your vehicle:

  • The make of the vehicle, for example, Toyota, Chevrolet, and so on.

  • The model, for example, Prius, Malibu, and so on.

  • The model year

  • The number of cylinders and type of engine

  • Whether the vehicle has an automatic or a manual (standard) transmission

  • The engine displacement, meaning, how much room there is in each cylinder when the piston is at its lowest point? (For example, a 3-liter 6-cylinder engine has a displacement of one-half liter, or 500 cubic centimeters — usually shown as 500 CCs — in each cylinder.) The bigger the displacement, the more fuel and air the cylinders in the engine hold.

    The displacement of engines on older vehicles may be listed in cubic inches, such as 302, 350, 454, and so on. Modern vehicles are usually listed in liters (1.8, 2.3, 5.9) or cubic centimeters (2200, 3400, 3800).

  • The kind of fuel system. If your engine is fuel-injected, you may need to know whether your car has throttle body injection or multi-port injection. Carburetors, on the other hand, were distinguished by how many “barrels” they had.

  • The spark plug gap. This is the amount of space that there should be between the center and side electrodes of each spark plug.

  • The part number for the spark plugs designed for your vehicle.

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The Essentials of Replacing and Gapping Spark Plugs

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