WHAT IS AN OEM PLUG

Original Equipment Spark Plugs

When you change your spark plugs, should you use the same brand and part number as the original, or a different brand?

Most professional technicians say they usually replace same with same, unless there is a reason to install a different brand of spark plug. If you use the same spark plug that the engine came equipped with from the factory, you should not have any problems with spark plug Fouling, misfiring , detonation or pre-ignition

When a vehicle manufacturer chooses a certain spark plug for an engine, the plug has to undergo extensive validation testing to make sure it does not run too cold and foul, or run too hot and cause detonation or Pre-ignition, or suffer misfiring due to electrode position or wear. Most original equipment spark plugs today are platinum or iridium and have a recommended replacement interval of 100,000 miles. So the validation testing is designed to simulate that kind of mileage before the plug receives its stamp or approval.

SPARK PLUG BRANDS

Years ago, most vehicle manufacturers used only one brand of spark plugs in their engines:

AC Delco in GM engines

Motorcraft or Autolite in Ford engines

Champion in Chrysler engines

Bosch in European makes

NGK or DENSO in Asian makes

In most cases the vehicle manufacturer either owned the spark plug supplier, or had a long historical relationship with that supplier. But globalization and competition has changed that once-cozy relationship. Today, you may find some GM or Ford engines factory-equipped with Bosch spark plugs, Mazda engines equipped with Motorcraft spark plugs, Chrysler engines equipped with NGK or DENSO spark plugs, and so on. Most late model Saturn engines use NGK spark plugs. Kia and Hyundai may come factory-equipped with either NGK or Champion spark plugs. Some vehicle manufacturers still rely on a single spark plug supplier, but most use a mix of suppliers, even for the same engine.

For example, a late-model Chrysler V6 may come factory equipped with a Champion spark plug, a NGK spark plug or a DENSO spark plug. All are “factory approved” for the application, so which plug is used on any given day may depend where the engine is assembled, which supplier shipped the vehicle manufacturer a container of spark plugs that day, and so on.

WHICH BRAND OF SPARK PLUG IS BEST FOR YOUR ENGINE?

Here is another fact some people have a hard time digesting: No one brand of spark plug is superior to any other brand. This does not mean any brand of spark plug will work in any engine. The heat range of a replacement spark plug (ANY brand) must be a close match with the original spark plug (ANY brand) for good ignition performance. The electrode configuration can be different as can the materials used to make the electrodes, but the electrode gap(s) must not be too wide or too narrow for the air/fuel mixture or firing voltage capabilities of the ignition system. The electrodes on the replacement spark plugs should also be capable of lasting at least as long as the original spark plugs.

The best advice we can offer is to use the same brand and type of replacement spark plug as the original spark plugs that came in your engine, unless you want to upgrade standard plugs to long life platinum or iridium spark plugs.

If the spark plugs have already been replaced at least once in your engine, and you are not sure they are the same brand as the original, or you don’t know what brand the original plugs were, ask an auto parts store employee to look up the plugs for you in their data base. Most list the original equipment spark plug along with any other brands the store carries that may also fit your engine.

If you want a certain brand of spark plug, but the spark plug manufacturer does not list one of their spark plugs for your engine, there is a reason why. Either they do not make a plug that fits your engine, or the plugs they have do not have the correct heat range or electrodes for your engine.

DO NOT try to match plugs by visual appearance. Two different brands of spark plugs that seem to be identical on the outside (same diameter and thread pitch, same type of electrodes, same length) may have differences inside that create a significant difference in heat range.