Tinker Talk – May 2019

By Justin James

An engine’s spark plugs are a small component tasked with a big job. Being able to understand them can turn out to be useful. In this edition of Tinker Talk we will go over the basics of spark plug electrode material, heat range and inspection.

Inspection: Spark plugs should be inspected at the specified service intervals or any time an engine is running poorly. Remove the spark plugs from the engine to inspect the electrodes and insulator tips (refer to Photo A). What you see here can tell you quite a bit about what is going on in the combustion chamber.

• Normal (Photo B): Brown or grayish tan deposits. Cheers to a happy engine.

• Carbon Fouled (Photo C): Black, dry deposits. This can be caused by a rich mixture, excessive time spent at low RPMs, timing issues or too cold of a plug.

• Burned (Photo D): White deposits and/or blistering. The chamber is getting too hot and is approaching the danger zone. This can be caused by engine overheating, too hot of a plug, a lean mixture or timing issues.

• Oil Fouled: Black, oily deposits. Engine oil is making its way into the chamber.

Electrode Material: Spark plugs are typically offered in copper, platinum and iridium. All are good conductors of electricity. Platinum can withstand temperatures of up to 3,000 degrees Fahrenheit. Iridium is essentially glorified platinum and can withstand temperatures of up to 4,000 degrees Fahrenheit. Platinum and iridium plugs do not offer any noticeable performance benefits under normal conditions, but they do tend to last significantly longer than copper plugs.

Heat range: Heat range is something that should only be tinkered with under extreme circumstances. A healthy engine will almost never require, or benefit from, a spark plug that is hotter than what is recommended by the manufacturer. Colder plugs typically only need to be installed when the engine’s power output has been significantly increased. Refrain from altering the spark plug heat range to overcome more significant issues such as incorrect timing, burning oil or incorrect air/fuel mixture.

The amount of information about spark plug composition and function spans far beyond what you have read here. This article is aimed at answering some of the questions that are difficult to find accurate information on. Hopefully this helps you next time you inspect or replace spark plugs.

Tinker, Shred, Destroy, Repeat

-Justin James

(follow more of my Tinker shenanigans on Instagram @justinjamesmoto)