Car Care Advice

How to Replace Spark Plugs In Four Easy Steps

Knowing How to Replace Spark Plugs Is an Intermediate Level Repair for DIYers, and This Maintenance Item Should Take Less Than an Hour To Perform On Most Vehicles.

  • DIY Difficulty Level: Intermediate
  • Time Required: about an hour
  • Tools & Materials
  • ratchet
  • extension
  • spark plug socket
  • spark plug gap gauge

What Are Spark Plugs?

new spark plug versus old, worn-out spark plug

To put it simply, the spark plug is as important to your engine as the gasoline in your tank. As its name suggests, the spark plug creates a spark in the combustion chamber to ignite the air/fuel mixture, which drives your engine.

Most engines feature one spark plug per cylinder, but some newer, more advanced engines feature two spark plugs per cylinder. This job is a routine maintenance item , and knowing when (and how) to replace spark plugs will help keep your engine running smoothly

How to Choose New Spark Plugs

emissions sticker showing the brand and gap recommended for spark plugs

Before changing the spark plugs in your vehicle, you’ll need to purchase new ones. Unless your vehicle’s engine has been modified, the easiest way to choose new spark plugs is to use what the manufacturer recommends. The emissions sticker under the hood usually has this information, but if the sticker is missing from your vehicle, your local parts store can definitely look this information up for you.  

When replacing the spark plugs, you should also replace the spark plug wires (if your vehicle is so equipped).

Is It Safe to Drive with Old Spark Plugs?

Only in the most absolute worst-case scenario would an old spark plug create a safety issue or cause damage to your engine, but worn out spark plugs will definitely affect the performance of your engine. If you don’t replace the spark plugs at the recommended intervals, you’re most likely going to suffer from a rougher idle and reduced fuel economy, but waiting too long could result in reduced reliability and even being stranded on the side of the road.

In short, why is this job important?

Spark plugs are what keep your engine going, so you definitely don’t want to forget about this service. The national average cost to replace spark plugs  is estimated to be between $191-$250. The complexity of replacing spark plugs depends totally on the type of vehicle you’re working on. On most vehicles, replacing the spark plugs should take about an hour, and doing this job yourself could save upwards of $100 in labor costs!

When to Replace Old Spark Plugs?

a worn out spark plug in need of replacement

Recommendations vary by automaker as well as vehicle type and severity of duty, but generally speaking, most vehicles should have the spark plugs replaced every 30,000 to 60,000 miles. Some of the more advanced engines with higher-priced spark plugs can go up to 100,000 miles.  

What Are Common Symptoms Indicating Worn-Out Spark Plugs?

  • Engine runs rough
  • Check engine light for cylinder misfire
  • Decreased fuel economy
  • Mileage determined by manufacturer’s preventative maintenance schedule
  • Visual inspection shows worn out spark plugs

How To Replace Spark Plugs

Step 1: Remove spark plug wires/coil packs

view of cylinder head with coil pack removed and spark plug installed

Depending on the type of vehicle you’re working on, the spark plugs could use either plug wires or coil packs. Regardless of which type of spark plug connection your engine has, use extreme caution when removing the wire or coil pack.

Pro tip: For vehicles that use plug wires, work on just one cylinder at a time. Remove the plug wire from the spark plug, replace the spark plug, and then reattach the plug wire. This saves a lot of time and eliminates the possibility of crossing wires, which will lead to an engine misfire and a check engine light.

Step 2: Remove spark plugs

specialty spark plug socket set

Pro tip: Before attempting to remove the spark plug, use compressed air to blow any dirt or debris out of the cylinder head area. This will prevent any dirt or debris from falling into the cylinder or into the spark plug threads.

Use a spark plug socket to remove the spark plug. These specialty sockets feature a rubber insert to hold the spark plug during removal and reassembly. Try to keep the ratchet and/or extension as straight as possible to avoid breaking the top of the spark plug off.

inside of a spark plug socket

Step 3: Check gap on new spark plugs

spark plug gap gauge

The spark plug gap is the distance between the center electrode and the ground electrode, and this gap varies among automakers, vehicles, and vehicle types. My Jeep has an emissions sticker showing the recommended spark plug type and required spark plug gap, but if your vehicle is missing this information, check the owner’s manual. 

Step 4: Install new spark plugs and reinstall plug wires/coil packs

View of cylinder head with spark plugs and coil pack installed

Ensure there is no dirt or debris on any of the threads, and then hand-screw the spark plugs into the cylinder head before attempting to tighten. Cross threading a spark plug can be a very expensive mistake. Follow manufacturer steps for installing new plugs, which means you don’t need to put anything on the threads such as anti-seize.

For optimal installation, you should use a torque wrench to properly tighten the spark plugs, but if you don’t have one (or there isn’t enough room for one), tighten until the spark plug feels snug. Just be sure not to over-tighten the plugs. 

Once the spark plugs have been replaced reattach the plug wires or coil packs.

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Jeffrey-Ross

Lifelong automotive enthusiast with a soft spot for offroading. Wrencher turned writer, but I still love to tinker on just about anything with an engine. Dream car: tie between a ‘71 Hemi ‘Cuda and a ’91 GMC Syclone. #GirlDad #SaveTheManuals

Jeffrey N. Ross
Lifelong automotive enthusiast with a soft spot for offroading. Wrencher turned writer, but I still love to tinker on just about anything with an engine. Dream car: tie between a ‘71 Hemi ‘Cuda and a '91 GMC Syclone. #GirlDad #SaveTheManuals

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