Q: What are the Different Types of Spark Plugs Available?

Talking about spark plugs is a never-ending discussion. Which ones are best? The answer to that question is somewhat trite, but can still be relevant depending on your vehicle and its intended use.

Spark plugs come in two basic categories: resistor and non-resistor. Three types of metal are used for their electrodes: copper, platinum (single and double), and iridium.

Resistor spark plugs are used for normal, everyday driving. One of the reasons for the resistor is to reduce the amount of electromagnetic interference induced into other systems on the vehicle, namely the radio.

Non-resistor spark plugs are generally used in high performance cars, like race cars, where quicker ignition system response is required.

Copper core spark plugs have been in use for over 100 years. They’re readily available, inexpensive, and work well in most engines. Copper plugs have a limited life span, generally about 30,000 miles before needing replacement.

When deciding on which copper plugs to use, conventional wisdom held different results for different makes: Ford vehicles worked best using either Motorcraft or Autolite spark plugs, GM used AC-Delco plugs, Chrysler used Champion plugs, european vehicles used Bosch, and asian vehicles used either Nippondenso or NGK spark plugs. With today’s more modern engine designs and higher performance ignition systems, copper core conventional wisdom is a moot point since these modern ignition systems don’t use copper core spark plugs anyway.

Copper plugs are generally the plug of choice on older vehicles (muscle cars, vintage, motorcycles, etc.).

Platinum spark plugs, both single-platinum (one platinum electrode) and double platinum (two platinum electrodes), are used for their longer service life. The platinum electrodes last much longer than copper. Back in 1992, GM released their Northstar series of engines, starting with Cadillac. This was the first engine with an advertised tune-up frequency of 100,000 miles. This claim was made possible due to the use of platinum-tipped spark plugs instead of copper. Performance improvements using platinum is negligible. The sole selling point of using platinum spark plugs is the extended life span. Platinum plugs are also more expensive than copper plugs.

Iridium spark plugs last longer than platinum plugs (roughly 15% longer) and are more costly than platinum. That’s where the difference ends.

Many people ask "Can I use a platinum spark plug in my old car?" The quick answer is "yes", but you may not want to. The copper plugs designed for older ignition systems were of a higher heat range than their equivalent platinum or iridium brothers. A hotter plug means it retains more heat in the core of the plug. Colder plugs shed heat more rapidly, keeping the plug "cooler." Using a platinum or iridium spark plug in an older engine may lead to the fouling of the plug rather rapidly because the plug is too cold to burn off any excess fuel and oil that get into the combustion chambers of the engine. Burning off extra fuel and oil is what the hotter copper core spark plugs did very well.

Today’s engines run cleaner and ignition systems are more powerful. The need for copper plugs doesn’t exist. Platinum plugs are the spark plug of choice for most vehicle manufacturers.

Still unsure of which spark plug to use? Just use whatever spark plug your vehicle manufacturer recommends and you should have no problems. If you need any assistance with your spark plugs, a certified mechanic can switch them out for you.