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How to Easily Spot Bad Spark Plugs on Your Vehicle

Spark plugs may be relatively tiny in the grand scheme of car parts, but they have a big job. A bad spark plug can make the difference in getting you from point A to point B.

Failing to maintain them can leave you and your vehicle high and dry when you need to go somewhere. 

Today, we’ll teach you how to save yourself a headache and easily spot bad ones in your vehicle. Let’s get started! 

What Do Spark Plugs Do for Your Car?

A spark plug sits in a cylinder head in your vehicle’s engine. One end of it connects to an ignition coil. This coil generates the voltage necessary to create a spark. The spark created from the ignition coil interacting with the spark plug will ignite the fuel. 

In the time it takes for you to snap your fingers, it has done its job multiple times. The spark lasts roughly 1/1000th of a second, and it ignites thousands of times every minute while your vehicle runs. 

What Happens When Spark Plugs Go Bad? 

A handful of things happen when your spark plugs go bad. Some are larger than others, but, ultimately, your vehicle will lack efficiency. However, by knowing what to watch out for, you can avoid a much more serious situation down the road.

Reduces Fuel Economy

If your spark plugs go bad, you could experience as much as a 30% loss in your fuel economy. Your bank account will definitely take a hit with the prices we see at the pump lately! It’s a good idea to reset your trip meter each time you fill up your tank. This will help you know what your fuel economy was for that tank.

Don’t forget that your fuel economy can change for various reasons. You may notice a drop in fuel if you’re towing, driving in stop-and-go traffic, or dealing with elevation changes. However, if you experience a reduction in your MPGs under normal driving circumstances, it’s a good idea to check your spark plugs.

Lack of Acceleration

Your vehicle uses complex computer systems to allow different components to communicate back and forth quickly. These systems tell the spark plug when to ignite when you’re accelerating. One that’s failing may not ignite or have a delayed ignition.

This will cause your car to run sluggish and not accelerate how you might expect. Generally, slow acceleration can occur for a variety of reasons. A qualified mechanic could quickly and rather easily test yours and let you know if that’s the issue or not.

Difficult to Start

There’s a whole lot going on behind the scenes when you insert your key and turn on the ignition. The simple act of turning your car key in the ignition starts a complex process that requires a complex system to work in harmony to start your vehicle.

However, a faulty spark plug can throw things out of sync and make it difficult to start your vehicle. If you notice your vehicle has troubles starting, don’t delay taking it to a mechanic. You don’t want the situation to worsen and cause more extensive damage. 

Loss of Power or Idling

A bad spark plug will cause your vehicle to lose power and sound rough when idling. You may also notice that the vehicle also vibrates significantly while idling. This is typically the result of a spark plug issue and a cylinder misfiring.

Again, take your vehicle to a mechanic to ensure it’s something as simple as a spark plug and not something more serious that will get worse.

Man repairing spark plugs.
It’s easy to spot a bad spark plug, but it can save you quite a headache in the long run.

How Do You Check Spark Plugs in a Car?

You’ll need a socket wrench, socket, and extender to check your spark plugs. They make special sockets with padding in them that protect it. But, if you’re careful, it’s not always necessary.

You’ll want to shut off the vehicle long enough for it to cool down. Then, wipe down the area around the spark plugs and clear away any debris. You don’t want anything falling into the cylinder once you remove it. Remove the wire from the spark plugs and place the socket over it to loosen it.

Once you remove them, look for any cracks in the porcelain, damage to the threading, or any burns to the electrode.  If the electrode is a little dirty, wipe it down with a rag before putting them back into the cylinder if there is nothing wrong with them. Replace any plugs that have damage to them.

Pro Tip: Need help changing your spark plugs? We uncovered Should You Avoid Mobile RV Repair?

How Often Should You Change Spark Plugs?

Standard spark plugs typically last anywhere from 10,000 miles to 30,000 miles. However, more expensive and higher-quality ones can last upwards of 60,000 miles to 100,000 miles. 

While it’s typically not included in an oil change, it’s a good idea to have your spark plugs checked every other oil change. This can help catch any issues with yours and keep your vehicle running smooth.

Spark plugs under a magnifying glass
Spark plugs might be small, but they have a big impact on your vehicles performance.

Can You Clean Spark Plugs?

Because spark plugs play such an important role in the engine of your vehicle, you want them to be as clean as possible. You can use various abrasives to clean yours.

Using 220-grit sandpaper is a good way to keep the electrode clean. You want the electrode to look shiny like bare metal. Keep sanding until it does. If sandpaper isn’t able to do the trick, it’s likely time to replace the spark plugs.

You should also use a wire brush on the threads of your spark plugs. This will help remove any oil or grime that have found their way onto it. It’s also a good idea to wear gloves while doing this to avoid poking yourself with the wire brush. Spraying brake cleaner on your spark plugs can also help remove dirt and debris.

Pro Tip: We spoke to an RV mechanic, these are the RV systems he says will break first.

How Long Do Plugs Last? 

There are typically three standard types: copper, silver, and iridium. Standard ones use copper and typically last 10,000 to 20,000 miles. Silver plugs are usually used on older vehicles and typically don’t last much past 20,000 miles. Long-lasting and expensive iridium plugs can last upwards of 60,000 to 100,000 miles.

How Can You Tell if a Spark Plug Is Firing? 

As you can see, there are some relatively easy ways to spot issues with your spark plugs. If you don’t keep up on your maintenance or pay attention to your vehicle, it can take a toll on your vehicle. It will not only ride rougher, but you’ll experience a loss in fuel efficiency.

Do yourself a favor and keep an eye on these signs of failure so you can keep your vehicle running smoothly. 

When was the last time you changed your spark plugs? Drop a comment below!

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  1. Sam Fitzwater says:

    If any build up is on it , that’s bad and if the plug is wet , it’s not firing replace it , but if your going to pull them out. For the cost of standard plugs I would replace them .I have always kept a few old one incase of issues . When your away from home it’s better to have a old one than none, it could get you to a service area.