How to Replace Spark Plugs? – DIY Auto Service Guide

How to replace spark plugs

A spark plug is a small metal insulated part that is bolted into the engine’s cylinder head. This small component was first made by Oliver Lodge in 1903 to generate the spark needed to ignite the mixture of air and fuel in the engine’s combustion chamber.

When the piston in the cylinder goes down it draws in that mixture of fuel and air, then when it comes back up it compresses it. Both the fuel and air are ignited by the spark generated when the piston reaches its TDC (top dead center).

Like every vehicle component, spark plugs have a certain lifespan. That’s why you will find this spark plugs replacing guide useful!

When to replace spark plugs


Usually, spark plugs need to be changed about every 80,000 miles (130,000 km) while some are going to be rated at 30,000 miles (50,000 km).

But certain symptoms can indicate that you’ll need to perform some simple car maintenance even before a car spark plug reaches the end of its lifespan.

Engine Light

For example, your engine light could come on or start flashing which is a very common symptom that there’s something wrong either with the spark plug or plug wires. This could mean that the engine is misfiring which can cause an increase in exhaust emissions or uneven power when accelerating.

Trouble Starting & Filling up Gas

If you are having a hard time starting your vehicle it means that the spark is worn out or damaged. Whilst it can also be an issue with the battery, you should check the plugs first as they do a very important job and are located at the heart of the engine.

In case you are filling up your gas tank more often than you used to, it means that the spark plugs are near the end of their lifespan. This causes an increase in fuel consumption as they are not very effective at burning the fuel that’s coming into the engine.

Rough Idling & Acceleration Issues

A change in how your vehicle sounds when you are stationary can tell you a lot about the state of the spark plugs. If your vehicle is making pinging, rattling, and noises similar to someone knocking, your spark plugs are probably in a need to get replaced.

Acceleration issues may come in the form of delay in vehicle responsiveness. A worn-out spark plug will not give you that instant acceleration and it will make your vehicle sluggish, which, of course, means that you need to replace them.

How to Change Spark Plugs

Removing the Old Ones

1. When you open the hood, the spark plugs are going to be located on the engine compartment underneath wires with plug covers on them. On 4-cylinder engines you will find every car spark plug set in a row either on the top or the side of the engine.

On 6-cylinder and 8-cylinder engines you’ll find them separated evenly on each side of the engine. On inline 6-cylinder engines, spark plugs are either on the top or side of the engine head. Some cars have engine covers which you’ll have to remove in order to get to the spark plugs.How to replace spark plugs

2. In case you’ve been using your car prior to this, make sure you leave it to cool down as the plugs and manifold can be extremely hot.

While you are waiting to start with this vehicle maintenance, gather all the necessary tools such as an extension bar, spark plug socket, a feeler gauge (spark gap gauge), and a ratchet socket drive wrench. Once the engine is cool to the touch it’s time to remove the spark plugs.

3. To remove a spark plug, pull one of the wires on the engine compartment by holding it as close to the bottom as you can. Be careful when doing so, to avoid damaging the spark plug head.

Get your socket wrench and together with the extension bar and ratchet remove the spark plug from the housing with caution. Use the feeler gauge to check the gap of the plug which should be between .028 inches (0.7 mm) and .060 inches (1.52 mm). Depending on the type of plugs and vehicle, there should also be a bit of wiggle room too.

Installing New Spark Plugs

1. Before you insert the new plugs clean up around the threads and the wire terminal. Also, check for any wear on the wires and use a wire brush or a can of compressed air to clean around the wire connections.

Before you install the new plugs, make sure to lubricate them with an anti-seize lubricant, especially if you are installing them in an aluminum engine.

2. Using the spark plug socket insert the new plugs and tighten them with a 1/8th of a turn. Do not overtighten them as this can strip the thread on the head of the engine.

Once that’s done, remove the masking tape and make sure you replace the spark plug cables that were initially placed on each plug. Lastly, place the spark plug wire boot back by pushing on it with a little bit of force so it snaps on.



By attempting this DIY Replacing Spark Plugs, it’s obvious that you will need the correct tools and protective gear for your safety. If you do not have all the gear for this, consider taking your car to a pro.

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