The Pros & Cons Of Hotter Vs. Colder Spark Plugs
The spark plugs in a gasoline engine are not universal, one-size-fits-all components. Plugs are made of a variety of materials with different electrode setups and thread configurations, and knowing the right spark plug type for your car can help maximize your engine's performance and efficiency. Most should work effectively for between 30,000 and 100,000 miles, but a need to replace your spark plugs more frequently might indicate that the ones you're using are too hot or cold for your engine. There's nothing to be gained by using a hotter or colder plug than is called for in your owner's manual, but you'll likely have problems if you stray from this recommendation.
For instance, using a plug that's not hot enough for your engine will lead to carbon fouling, while a plug that's too hot can cause fatal engine or valvetrain damage. It's why we strongly recommend sticking to the recommended spark plugs in the owner's manual unless you've made modifications to the engine. Changes to air and fuel intake systems might mean you need a hotter spark plug to prevent fouling, and the same applies if you retard the ignition timing. Advancing the timing will raise internal combustion temperatures, potentially also requiring the switch to different spark plugs. It's the same with changes in compression ratio; higher ratios mean higher combustion temperatures inside the cylinder. Whether or not an engine uses forced induction and how you drive also come into play regarding spark plug temperatures.
how to identify a plug's temperature range varies by manufacturer. NGK spark plugs have a numbered heat rating, with 1 designating the hottest plugs and temperatures dropping as the heat rating number climbs. For example, a 2010 Mitsubishi Galant uses NGK LZFR6AI Lazer Iridium spark plugs with a heat rating of 6. This indicates a colder plug that is suitable for engines with higher compression ratios like the 9.5:1 ratio on the Galant's 2.4-liter four-banger. Using a different plug may result in poor fuel economy and lackluster acceleration.
Regardless of manufacturer you can tell a cold plug from a hot one by the length of the insulator nose, the white ceramic collar that covers most of the center electrode. Hot plugs have longer insulator noses that help contain heat for more efficient fuel/air combustion, while cold plugs have shorter noses to allow more heat to escape.
If a spark plug tip gets too hot, the fuel/air mixture can ignite prematurely. This is called "pre-ignition" and can damage engine internals or valves. Plugs that run too cold won't combust all the fuel and will become fouled with carbon deposits, reducing the intensity of the spark. For most spark plugs, the optimal firing temperature will be between (500º and 800ºC (about 900-1,500ºF). Before you buy a set of "performance" spark plugs for your car, know that spark plugs marketed in this way won't necessarily boost engine output. They can complement certain engine mods well, although you might need to experiment with a couple different plugs before you find the sweet spot between fouling and overheating. You should also make sure the spark plug gap is correct before installing each plug.
