A spark plug sits above each cylinder head in your engine and “fires” to ignite the compressed fuel and air mixture in the cylinder. The spark plug doesn’t actually touch the mixture; instead the electrical spark travels over a small gap (usually about a millimeter) to initiate the combustion. The force of this mini-explosion drives the piston down, creating power. Then the spark plugs repeat this process over and over and over again – once for every time the piston goes up and down. Usually an engine has one spark plug per cylinder, but some engines may have two spark plugs per cylinder. Without spark plugs, your Subaru won’t start or continue to run.

Keep in mind. You can’t just use any spark plug in any engine. See what your Owner’s Manual says and follow it!

• Copper Spark Plugs: These are the most basic spark plugs. Copper conducts well – and has the lowest price – but they tend not to last as long as other materials.
• Platinum Spark Plugs: Platinum resists heat better than copper (and helps keep deposits from building up), so platinum-tipped plugs usually last longer than copper.
• Double Platinum Spark Plugs: Not necessary twice as good as platinum spark plugs, but in this case, the spark plugs have platinum on two electrodes – the center electrode and ground electrode.
• Iridium Spark Plugs: Iridium is harder and more durable than platinum. (Costlier too!) Because of the cost of iridium, the electrode is thinner, but they still deliver better power, better combustion and longer life than other plugs.

Conditions inside an engine are predictably brutal. As much as modern engines are engineered and built to reduce friction among moving parts, friction – and the heat that goes hand-in-hand with friction – is unavoidable as cylinders get pumping. Depending on engine speed, spark plugs fire 1000 times or more every minute. Wear and tear is a real issue.

No matter how efficient an engine is, a tiny bit of material is left after each combustion. These deposits build up on the spark plugs over time, resulting in uneven performance and even lower gas mileage. In addition, the gap that a spark has to travel to ignite the fuel/air mixture gets larger and larger as the spark plug ages thanks to heat, particulates and normal wear and tear.

That’s why it’s important to have your spark plugs checked (and replaced) according to the manufacturer’s maintenance schedule. Superior materials may have extended the average spark plug’s life, but they won’t last forever.

You like it when your Subaru runs, right?

But beyond the obvious reason, replacing the spark plugs has some ongoing benefits.

• Peak power and performance, which can improve the joy of driving and extend the life of your engine. Start confidently – drive confidently.
• Optimal fuel economy, which can save you money. Squeeze every mile out of every drop.
• Less pollution, which can help the environment. Better combustion leads to lower emissions.

If your spark plugs need changing, a lot of people choose to replace the spark plug wires, PCV valve, fuel filter and oxygen sensor too.

Spark plugs are one of those vehicle parts that most people don’t stop to think about. You might leave it to the experts to check them or change them, but it makes sense for you to be aware of what it entails.