Subaru Spark Plugs: OEM Vs. Aftermarket

When it’s time to replace the spark plugs in your Subaru, the first decision to make is whether to get OEM or aftermarket replacement spark plugs. Aftermarket spark plugs are typically cheaper. But, you’re not really getting the most value in terms of longevity and reliability.

OEM spark plugs offer the most bang for your buck when you take into consideration the 2 most important factors to look for in a spark plug:

1. Quality of the Components

OEM plugs

If you’ve ever wondered why aftermarket spark plugs are inexpensive, it’s largely because they’re made with low-grade materials.

OEM Subaru spark plugs are built with the highest quality materials. Subaru understands the significance of using the right types of materials in spark plugs. When the aftermarket manufacturer compromises on quality just to save a few bucks, two major problems occur:

A. Electrical System Interference

The electrical voltage inside the spark plug is so high that the plug has to be built with an interference suppression resistor. Without a resistor, the electrical noise created by the spark plug while firing would interfere with your Subaru’s electrical system. This would create all sorts of problems, including:

  • Radio static
  • Navigation system issues
  • Malfunctioning sensors

Aftermarket manufacturers tend to use low-quality interference suppression resistors in plugs to keep costs down. Cheap aftermarket spark plugs may save you a few bucks at the cash register. But you’ll likely deal with electrical problems in your car until you upgrade to OEM spark plugs.

B. Reduced Lifespan

There are several important components inside a spark plug. Even one component that’s built with low-quality materials can kill the entire plug or cause other problems. For example, the lack of a nickel plating on the plug threads can cause the plug to seize inside the cylinder head. For that reason, it’s pretty rare for an aftermarket spark plug to last as long as an OEM spark plug.

2. Fitment

Replacing plugs

Image Credit: Scenic Driver

Aftermarket parts, especially spark plugs, are notorious for poor fitment. While fitment doesn’t matter much with some parts (like emblems, for example), it’s a huge deal with spark plugs. It’s because engine tolerances are so tight that spark plugs need to be the perfect size right down to the micrometer.

If you put in an aftermarket spark plug that’s the slightest bit longer or shorter than OEM specs, or if the electrode gap is even slightly smaller or bigger, you won’t be getting the most out of your engine. Performance and fuel economy will suffer. For starters, the electrodes on the spark plug can interfere with the pistons or valves in your engine if they’re too long. Electrodes that are too short won't completely ignite the fuel mixture, which reduces combustion efficiency.

All OEM spark plugs are made to OEM specs, meaning they’re exactly uniform in length and electrode specs. When you replace a bad spark plug with an OEM one, you’ll get optimal performance and fuel economy.

OEM Spark Plugs Don’t Always Have to be More Expensive Than Aftermarket Spark Plugs

Now that we’ve established that OEM spark plugs are superior to aftermarket spark plugs, we have some good news: genuine OEM spark plugs can be cheaper than aftermarket knockoffs! At least that’s the case at, where we carry genuine OEM Subaru spark plugs at wholesale pricing.