How Often Should You Change Your Spark Plugs?

First, what is a spark plug? It’s a part that plugs (actually, screws) into the combustion chamber of your gas engine (diesels don’t have spark plugs). The spark plug is energized for a brief instant by the ignition coils or coil packs.

When the spark plug is energized, the electric charge jumps from the centre electrode to the side electrode, also called the ground strap. When the charge jumps, it arcs, or sparks. That spark happens at just the right moment to ignite the air and fuel mix in your cylinder. This sets off the controlled explosion that makes your engine run.

Spark plug technology has come a long way from the nickel or copper-tipped electrodes of the 1970s. Back then, they needed to be replaced every year along with the many parts that made up a tune-up.

Today’s plugs use expensive new materials like platinum, iridium, ruthenium, and other exotic-sounding metals for the centre electrode and the ground strap of your spark plug. These metals last longer in the incredibly tough conditions inside your engine. They won’t melt, and they take longer to corrode and wear out.

Most importantly, these new metals offer better ignition, which improves your car’s overall performance. These high-tech plugs deliver better drivability, better combustion, and lower emissions, as well as longer life.

But, just like their ancestors, they still need to be changed. If your spark plugs aren’t changed, it can cause your engine to run poorly or misfire. It can also put a strain on your coil packs and other ignition parts, forcing you to replace those too.

Routine replacement

The easiest way to know when it’s time for a routine spark plug replacement is to check your owner’s manual. The people who designed your car or truck know when it’s best to replace your plugs.

Ford, for example, recommends replacing spark plugs every 160,000 km on the 2022 F-150. Toyota puts the first spark plug replacement for a 2022 Toyota Prius at 144 months or 192,000 km, whichever comes first. Older cars may require plug replacements after just 30 months or 48,000 km. Whatever the interval, it’s important not to leave your spark plugs in for longer than indicated.

Some experts like to change their spark plugs before the recommended interval. Their logic? Leaving your spark plugs in place for almost 200,000 km can make them impossible to remove. They also worry that the ignition coil pack boots will break down after all that time and then break when you try to remove them.

Since spark plugs are relatively inexpensive, there’s no harm in replacing them sooner than necessary.

Replacing a broken spark plug

Even though they’re made of high-tech metals, spark plugs can wear out prematurely. Problems in your engine like oil leaks, bad fuel, and even physical damage can all cause a spark plug to foul and fail.

Your first sign of a bad plug will probably be a higher bill at the gas pump. An engine that’s not running well will use more fuel.

Your second sign will likely be a check engine light. That orange glow is a sign there is something wrong with your engine. A flashing check engine light indicates a misfire, telling you one cylinder is not igniting when it should be. This could be due to a bad spark plug. A NAPA Autopro service centre can help you get to the bottom of the issue, or you can use an engine scanner tool.

There are two easy ways to tell if a spark plug is bad. The first is to pull it out and take a look at the tip. Here’s how to remove your spark plugs if you need a hand.

The tip of the plug (the part in the cylinder) should look brown or light gray. If you see anything else, like deposits, a broken electrode, worn surfaces, or oil, that’s a sign that the plug needs to be replaced. If there are deposits or oil on the plug, your engine probably needs more significant repairs. Your NAPA Autopro service centre can help.

If the plug is physically damaged or cracked, it needs to be replaced.

If you’ve checked the spark plug and it looks ok, your next step is to check the ignition coil, the part that sends power to the plug. Look for cracks, as these can let water in and send the electrical charge to the wrong spot.

Swap the ignition coil pack on the misfiring cylinder to another good cylinder. If the misfire stays, the spark plug likely needs replacement. If the misfire moves, then the coil pack is the problem.