Why properly installing your spark plugs is so important – Jalopnik

Sealing the spark plugs may sound like one of those old-fashioned chores, like installing break points in a distributor or lubricating the frame, but having the right spark plugs and making sure they are adjusted properly is a crucial part of the engine’s operation. Before we dive too deep, let’s start with some basics about spark plugs: They provide the ignition of the air-fuel mixture in most internal combustion engines. (You diesel people can sit this out; we’ll talk about glow plugs another time.)

The connecting nut is located at the top of a spark plug. This is where the spark plug wire, or the individual ignition coil in a coil-on-plug system, connects to the spark plug. The current flows through the plug to the center electrode at the bottom and then jumps to the ground electrode – that curved, semi-horseshoe-like part of the plug. That flow is what we need to control with the gap. Fine-tuning the gap between the ground electrode and the center electrode is what people are referring to when they say a spark plug is “between the holes.” Setting the correct gap can potentially prevent problems such as misfire, fouling, accelerated spark plug wear, poor fuel economy and reduced horsepower, all of which can result from too wide or too narrow spark plug gap. The trick is to be like Goldilocks and find the gap that is just right.

Turbocharged and supercharged engines tend to run hotter, as do high-speed engines, and with their high operating temperatures, cold spark plugs are usually the way to go. Low-speed engines, such as those in lawn mowers and ATVs, can use nice warm plugs to burn away deposits and keep the chambers clean. With a ‘hot plug’ the insulator (the white porcelain part) will be longer than with a ‘cold plug’. Because the insulator insulates, the more of it there is, the better it retains heat. Hot plugs push more heat into the combustion chamber and are better at burning away deposits, something that cold plugs can struggle with.

The specific gap set for your spark plugs will depend on a number of factors, including compression ratio, optimal spark advance, the quality of gasoline you use, the altitude at which the car is typically driven, and any adjustments you may have made, such as adding forced induction.

Feeler gauges are what you need for platinum and iridium plugs. When using feeler gauges, never attempt to use the gauges to enlarge the opening; the gauge will just bend. For the convenience of a coin tool and the accuracy of a feeler gauge, you can purchase a wire loop tool. It’s shaped like a coin, but it has loops of wire of varying thickness sticking out of it, so you can get exactly the opening you want. But if you need to fit the plug to an odd size, that wire tool can leave you hanging because there is only room for a small number of loops.

To close the gap between your spark plugs, you can gently tap the ground electrode against something hard, heavy, and immovable, such as a vice. To loosen the opening, use the prying part of your splitting tool or pliers. You’ll know the opening is correct when your measuring tool requires a good tug to pull it out. Think of it as a good handshake. You don’t want the loose and unpleasant ‘limp fish’, nor the tight ‘phalange cruncher’.