Get a quote
Maintenance and gear

How spark plugs work and what they can tell you about your engine | DIY

by Hagerty
27 April 2021 3 min read

The humble spark plug is well over a century old, but its technology and function have remained unchanged. Learning how a spark plug works and what it can tell you about your engine is critical, even in the age of highly intelligent, computer-controlled engines. From heat range to material, we are here to share what you should know about these hardworking components.

How much is your car to insure? Find out in four easy steps.
Get a quote

Construction

From the outside, a spark plug appears very simple and, in a few ways, it is. The top of the plug is a cap, and the spark-plug wire attaches to it. The cap also connects to the electrodes that run through the centre of the ceramic porcelain insulator. The final piece is the threaded case that holds everything and creates the grounding connection. The electrode pokes out the base of the plug in line with a small ground strap (also known as a ground electrode or side electrode), thus providing a clear path for the high-voltage arc to follow and ignite the fuel and air mixture in the cylinder.

We can’t talk about spark plug construction without mentioning heat ranges. The basic thing to keep in mind here is that a “colder” plug snaps off the same spark energy as a “hotter” plug. Heat ranges have nothing to do with energy and everything to do with keeping the plug clean. Ideal operating temperature for a spark plug is between 500 to 800 degrees C. This is hot enough that the porcelain ceramic that surrounds the electrode tip in the combustion chamber can burn off any contaminants or combustion byproducts that stick to it.

A colder plug has more insulation and therefore transfers more heat away from the electrode into the cylinder head or engine block. Too cold, and the contaminants build up and foul the plug; too hot, and the porcelain will crack and degrade.

Types

There are four main types of plug construction: copper, platinum, double platinum, and iridium. Each step up brings a price increase, but also greater durability and spark energy. The shape of each is unique and, if you’re pulling apart an unknown engine, can help you identify which kind of plug you’re looking at. The shape of the electrode is the most obvious tell; to differentiate between a platinum and a double platinum plug, look for the disc on the ground strap.

There are also two types of sealing mechanisms: a crush gasket and a conical seat. The crush gasket is the most common and the simplest. The conical seat is reasonably rare and should only be used with cylinder heads that have been cut with a matching seat; if you’re used to crush gaskets, you may find the torque specification for conical-seat plugs surprisingly low.

Reading

A spark plug can tell you a lot about the running condition of an engine. A buildup of oil or other contaminants can cause a plug to foul and stop firing, while a worn-out plug can misfire after the electrode and ground strap are consumed over many hours of use. Pulling the spark plugs is a simple task on most engines, so even if the engine seems to be running normally, a quick check won’t hurt.

The spark plug is a critical piece in a standard non-compression ignition engine. Understanding this humble component goes a long way to helping you understand how to keep your engine in top shape or, if you’re looking for more power, to tweak its performance. There are more information-packed DIY videos coming, so be sure to subscribe to the Hagerty YouTube channel to never miss an instalment.

Via Hagerty US

Also read

Socket Set: How to lift a car safely
Socket Set: A beginner’s guide to changing brake fluid
The Revival Guide: How to get your classic car ready for the road

You may also like

Socket Set: How to check and change spark plugs
Socket Set: How to check and change spark plugs
Elbow Grease Alcantara
Elbow Grease: Brushing new life into Alcantara
Socket set ignition system
Socket Set: Maintaining your car's ignition system
A story about

Your weekly dose of car news from Hagerty in your inbox

Leave a Reply

Your email address will not be published. Required fields are marked *

More on this topic
Share

Thank You!

Your request will be handled as soon as possible