It’s important to make sure that your spark plugs have the right gap when you are doing an engine tune-up. When you buy spark plugs, they may not necessarily have the right gap between their electrodes for your engine. Having the wrong gap can cause your engine to misfire, lose power, and run less efficiently, which lowers your gas mileage.
Check your car or truck’s owners manual for the recommended spark plug gap for your engine.
You’ll also need some special tools to get the job done.
You can use either a feeler gauge or a spark plug gauge to gap your spark plugs.
Types of Spark Plug and Feeler Gauges
A feeler gauge is made up of thin metal blades of different thicknesses joined together like the blades of a pocket knife. Each blade is a precise thickness, and may be marked in millimeters or thousandths of an inch. To gap your spark plugs with a feeler gauge, you will also need a pair of pliers (a pair of straight-handled pliers works best). Depending on the feeler gauge you get, some have wire loops and a bending hook designed especially for gapping spark plugs.
The pros of using a feeler gauge is that it’s more accurate than ramp-style spark plug gauges, and that most feeler gauges have enough different blades to measure almost any gap. So, if your vehicle has an odd-sized gap, a feeler gauge will likely still have a blade that’s the right thickness to handle it.
The cons of using a feeler gauge is that you need a pair of pliers for bending the spark plug electrode, since the feeler blades will bend if your try to use them for bending the electrode. A feeler gauge is also more expensive than spark plug gauges are.
Spark plug gauges come in two main types.
A ramp-style spark plug gauge looks like a silver dollar with numbers marked all around the edge of its face, and a thin outer edge that has a gradual change in thickness all the way around the coin.
These are the least expensive gauges for gapping spark plugs, and you can bend the electrode with them, so you don’t need any other tools. However, they are the most difficult to read and the least accurate gauges, mostly do to the gradual slope of their measuring and bending edge.
Wire loop-style spark plug gauges also look like a coin, but they have several wire loops of different thicknesses all around their outside edge, and a driver or hook to bend the electrode on a plug.These gauges are as accurate as a feeler gauge, and they don’t need a separate tool for bending. They are also less expensive than feeler gauges. However, they only have a limited number of loops, so if your engine needs an odd gap size, a loop-style spark plug gauge may not have a loop to fit it.
Essentially, which gauge you use is up to your own personal preference. Each gauge has its own pros and cons for gapping spark plugs.