How to Know When To Replace Your Mazda Spark Plugs

Mazda spark plugs last about 75,000 miles, give or take. When a spark plug goes bad, the engine's performance suffers and you'll notice an increase in fuel consumption.

So when you suspect that at least one of your spark plugs isn't firing as well as it should, it's worth taking the time to pop the hood and check all the spark plugs in your engine. Read on to find out how.

Telltale Signs of Bad Spark Plugs

Old plugs

Luckily, the first indicators of spark plug issues are easy to spot. The most common symptoms include:

  • Misfires
  • Poor gas mileage
  • Loss of power
  • Slow acceleration
  • Difficulty starting the car, especially in winter time

How to Check Your Spark Plugs

Because spark plugs are installed in the cylinder head, a lot of people are intimidated by the idea of pulling their spark plugs out and inspecting them. The process is so much easier than it sounds. The only special tool you would need (in addition to basic hand tools) is a spark plug socket. You can't use a regular socket because they are not deep enough. Also, spark plug sockets contain a little rubber bushing specifically designed to grip the spark plugs and remove them from the cylinder head without damage.

Finding the Spark Plugs

Before you can inspect the spark plugs, you have to take them out of the cylinder head. Here's a general overview of how the process goes:

  1. Open the hood.
  2. Remove the plastic engine cover. In most cases, the cover has Mazda's logo on it.
  3. Underneath the cover are some spark plug coils. They sit directly on top of each spark plug. Remove the 8mm bolts keeping the coils in place.
  4. Unplug the connectors on the spark plug coils.
  5. Lift the coils straight off the spark plugs.
  6. With a spark plug socket, remove the spark plugs.

Now with the spark plugs in front of you, it's time to visually inspect them for signs that they've gone bad.

Inspecting Your Spark Plugs

Image Credit: Oliver Porter

First, let's talk about what a good spark plug looks like. First, find the insulator (the white part inside the spark plug that's wrapped around the central electrode protruding into the combustion chamber) and then note its color.

If the spark plug is still good, the insulator will be grayish white, yellow, or light brown. There will be no buildup on the insulator or anywhere else on the spark plug. It won't have any cracks. There won't be any corrosion anywhere.

If you see any of the following on a spark plug, that means it's bad:

  • Corrosion on the electrode or anywhere else
  • Carbon build up on the insulator (which looks like black velvet)
  • Motor oil anywhere on the spark plug
    • This usually means that the cylinders, valves, or piston rings are worn.
  • Yellow build up on the insulator
    • This usually means that there's lead in the fuel
  • Melted electrode
  • Cracks on the housing or anywhere else
  • Bent electrode

Replacing Your Spark Plugs

Have you determined that one of your spark plugs is bad? If so, it's strongly recommended to replace all of your spark plugs at once. Luckily, you can buy genuine OEM spark plugs online for much cheaper than dealership prices. As authorized sellers of genuine OEM Mazda parts, we carry OEM spark plugs at very competitive prices. Look up your Mazda model in our catalog to find the right spark plugs for your car!