How to Know When It's Time to Change Your Spark Plugs

For such small car parts, spark plugs handle a big job. When your vehicle is having certain problems (we’ll get to those later), it’s common to overlook the spark plug as a possible culprit. But spark plugs are a critical part of your car’s motor function and need to be checked regularly. If you’re not having them cleaned or changed as needed, you could end up with a vehicle that has trouble starting in the morning, doesn’t accelerate properly or has other issues that can result in a big auto repair bill.

Servicing your spark plugs and having them replaced before they compromise your vehicle’s function is a great way to keep your car running well and ensure you don’t end up stranded.

Understanding what your spark plugs do is the first step in understanding why they’re so critical to your car’s performance. Once you know what they do, you can also learn how to take care of them properly and what to look out for.

What Do Your Spark Plugs Do?

Even if you don’t have an electric car, your vehicle runs on electricity — and it depends on your spark plug to provide it. When you fire up your engine, your spark plugs send out a small bit of electricity that provides the ignition your car needs to start. Without that spark, your car’s not going anywhere (and that means neither are you).

Spark plugs are on the top or side of the engine on four-cylinder and inline six-cylinder machines, and are separated on each side of the engine in V6 and V8 engines. In some cars, you may have to remove an engine cover to see the spark plug wires.

Because of their location, spark plugs are forced to endure incredibly hot temperatures and high pressure, and are designed to burn off such things as fuel additives or other types of contaminants they might be exposed to in the engine. When they’re doing their job, they go unnoticed and are taken for granted, but when they stop working, you’re immediately reminded of how important they are.

When Should You Change Spark Plugs?

Spark plugs are used every time you drive your car, so they start wearing down over time. The most likely component to wear down will be the electrode, which is the small metal rod coming out of the center of the plug. It has a metal hook on one side, which is where it sends the electricity upon ignition.

As the electrode wears down, it won’t create as much electricity. Eventually, if ignored, the problem will keep you from being able to start or drive your car, or you may have trouble accelerating. Typically, manufacturers will recommend that you change your spark plugs every 30,000 miles, but as with every rule, there are exceptions to that.

The type of material your spark plug is made from will affect its longevity. Copper is the least expensive metal and often will only last about 20,000 miles, while iridium and platinum plugs have the best lifespan. You’ll pay more for longer-lasting spark plugs, but you’ll also be able to replace them less frequently, too. Your owner’s manual should tell you what type of spark plugs are recommended, but you can also talk to a trusted mechanic about which plugs are ideal for your car.

Certain factors, like damage from overheating — which can happen if your engine’s air-to-fuel ratio is incorrect — can wear out your spark plugs faster. So can things like oil seeping onto the spark plug and carbon building up on the tip. Also, if you drive your car more aggressively, that can cause your spark plugs to work harder and wear out faster.

That’s why regularly having your spark plugs checked for wear is a good idea, even if you aren’t approaching the 30,000 mile mark.


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How to Tell if Your Spark Plugs Are Failing

In addition to a visual inspection from your mechanic, there are certain performance issues that can signal it’s time to take a look at your spark plugs. Here are six warning signs to watch out for:

  • Your engine isn’t idling smoothly. You want your car’s engine to purr like a kitten, not buck like a bronco. If your engine sounds rough and uneven, and you can feel vibrations in the car, you need to get to a mechanic pronto. This could be due to faulty spark plugs and can cause engine damage if ignored.
  • Your car won’t start. There are several reasons your car won’t start, but spark plugs are often overlooked as the possible culprit. Worn or bad plugs may not be able to produce enough of a spark to fire up the engine.
  • Your engine surges. If your vehicle takes in too much air during the combustion process, that can make the car jerk forward and then immediately slow down. It’s annoying at best and can be dangerous if it occurs in traffic, so don’t let this go unchecked.
  • Your fuel efficiency is off. Incomplete combustion caused by deteriorated spark plugs can decrease your fuel economy by as much as 30%. If you notice a sudden change in your fuel consumption, your spark plugs could be the source of the problem.
  • Your car isn’t accelerating properly. You can tell when your car is sluggish and doesn’t respond to acceleration. If your spark plugs are going bad, it may not accelerate, or it might take an extra few seconds before it responds. Instead of feeling like it’s ready to get up and go, your car might feel more like it’s being dragged or pulled.
  • Your check engine light comes on. Your check engine light is designed to alert you to a number of different potential problems in your vehicle; failing spark plugs is one of the things that can trigger the light.

Don’t Put Off Spark Plug Replacement

If your vehicle is showing any of these symptoms, or if it’s been close to (or more than) 30,000 miles since your spark plugs were inspected, make sure you schedule it as part of your next vehicle maintenance — and don’t put it off. Like everything else with cars, it’s always better to fix the issue before it causes problems instead of waiting for it to result in major repairs.


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