In this article, we’ll introduce the tools needed to change spark plugs on gasoline vehicles and explain how to do it. How is a spark plug change done. How is the correct spark plug chosen. What to watch out for when changing spark plugs? We’ve prepared this article, full of pictures and explanations, for drivers curious about these questions.
Changing Spark Plugs
The most important thing to watch out for when changing spark plugs is using a plug with the correct specifications — the right replacement part must be chosen. Examining the spark plug tips can reveal many engine faults and tuning issues.
Tools Needed to Change Spark Plugs
To change spark plugs you’ll need gloves, a spark plug socket, a ratchet — or a spark plug wrench, a flat-blade screwdriver, and a feeler gauge to check the spark plug gap. If possible, a torque wrench is preferred over a ratchet.
What sets a spark plug socket apart from other sockets is that it has a rubber insert inside. This lets us grip the spark plug and pull it out of its bore.
Standard Spark Plug Life
Standard spark plugs generally need to be replaced every 20,000-30,000 km.
Iridium/Platinum Spark Plugs
Thanks to their durability, iridium- or platinum-tipped spark plugs can last up to 80,000-100,000 km.
Importance of Torquing Properly
Installing spark plugs too loose or too tight can both ruin the seal and damage the cylinder head.
How Is a Spark Plug Change Done?
We’ve covered the tools needed to change spark plugs. So how is a spark plug change actually done?
First, we’ll remove the plastic engine cover on top. The air filter is inside this plastic cover. We find the mounting point and remove it.
We remove the connectors where the electrical wires plug into the ignition coils, from their sockets. If you don’t have a special tool for this, you can pop them out with a flat screwdriver as shown in the image. However, care is needed not to damage the connector housings.
After removing the connector from its socket, it’s time for the ignition coils.
The ignition coil steps up the electrical energy it gets from the battery to around 30,000 volts and delivers it to the spark plug. This high energy turns into a spark between the spark plug’s electrodes. (Image above)
We grab the ignition coil and carefully pull it straight up.
Once we’ve removed the ignition coil too, we can now access the spark plugs.
We fit the spark plug socket onto the plug inside, using an extension bar and a ratchet, and turn it carefully. Don’t move the socket wrench around too much while changing spark plugs. Try to keep the socket steady both when removing and reinstalling it. If it accidentally skips a thread, and you force it, you can damage the threads in the spark plug bore.
After removing the spark plugs, line them up on a tray, keeping their order straight, and examine the tips. It’s also worth checking the spark plug wires while you’re at it. Check the spark plug wires for cracks, burn marks, wear from rubbing, and make sure there’s no oil on them. If there’s cracking or wear on the spark plug wires, it’s a good idea to replace those too.
Choosing a Spark Plug for the Replacement
Since new spark plugs can vary by vehicle model, we’ll need the car’s catalog or manufacturing specs. Or we can remove the old plug and take it to an auto parts store to ask for the same part, new.
From what we’ve generally seen, Bosch or NGK brand spark plugs are preferred. You can find the right plug for your car on the manufacturer’s website. For example, you can use the link below to select the right spark plug for your car’s model.
Click here to choose the right NGK spark plug for your car model
Installing the New Spark Plugs
Install the spark plugs at the proper tightness. Spark plugs installed too loosely reduce cylinder compression pressure, which reduces engine power and increases fuel consumption.
The spark plug you buy will have the required tightening torque printed on it. If we’re using a torque wrench, we can set this force precisely. If we don’t have a torque wrench, let’s aim to tighten the plug with about the same force we used when removing it.
Spark plugs should be hand-tightened first, then tightened an additional 90 degrees with a wrench for new plugs, or 30 degrees for old plugs. For plugs with a tapered seat, the wrench-tightening angle is 15 degrees.
Once the spark plugs are replaced, we put the coils back in place. We reconnect the coil connectors and close the engine cover.
Before closing the engine cover, we also fit the air filter connection hose that’s on the engine cover back into place.
What Should You Watch Out for When Changing Spark Plugs?
In this section, we’ll try to answer common questions about changing spark plugs.
Should the Engine Be Hot or Cold When Changing Spark Plugs?
First and foremost, the engine must be cold — if it’s hot, wait for it to cool down. Never remove a spark plug from a hot engine; trying to do so can break the plug. The spark plug bore or its threads can be damaged, and the rubber part of the plug socket can tear from the heat. Trying to change spark plugs on a hot engine can also burn your hands.
What Should the Spark Plug Gap Be?
Even though a new spark plug bought from a parts store is new, its gap should still be checked with a feeler gauge and set to the correct value; all 4 spark plugs should have an equal gap.
Every different make and model has a different ideal gap. For example, spark plug gaps like 0.9mm, 0.8mm, or 1 mm. These values are usually printed on a label stuck to the inside of the engine hood. (Spark plug – GAP values)
The spark plug type and spark plug gap values shown on the label stuck to the engine hood (above)
The feeler gauge used to check the spark plug gap (above)
If this isn’t done, the engine will idle roughly, knock, lose power, and consume more fuel. The clearest sign of this fault is a rough idle and engine vibration.
Will a Double-Electrode Spark Plug Fit My Car?
What matters is fitting a spark plug that’s compatible with your car. You can select the right plug for your car on spark plug manufacturers’ websites.
What’s the Difference Between a Regular Spark Plug and an Iridium One?
Platinum or iridium spark plugs have a slightly larger gap than classic plugs (1 – 1.3 mm and similar), and their center electrodes are sharp-edged; if the center electrode has become rounded (taken on a circular shape), the plug should be replaced. Also, when setting the gap on platinum/iridium plugs, the gap should be adjusted without damaging the center electrode.
Does Changing Spark Plugs Improve a Car’s Performance?
My car’s power has dropped a lot. Will changing the spark plugs improve the power? For drivers asking this, here’s what we can say:
Since spark plugs are ignition components, their effects show up first in situations like initial startup and cranking. Depending on the problem with the plugs, they can also affect how the car responds when you press the gas. They can cause problems such as rough idling, knocking, reduced power, and increased fuel consumption. The clearest sign of a spark plug fault is a rough idle and engine vibration. After replacing your spark plugs, your car will use fuel a bit more efficiently. This will have a positive effect on power as well.
Is the Spark Plug Socket a Standard Size?
16 mm sockets are generally used. Some cars, however, use 14 mm sockets.
Related Questions
In a hot engine, the metal in the cylinder head has expanded, and removing a spark plug can damage the thread structure. There’s also a risk of injury from contact with hot surfaces, which is why this job should be done on a cold engine.
This gap determines the strength and reliability of the spark that forms between the electrodes. A gap that’s too narrow or too wide can cause weak or inconsistent ignition, reducing the engine’s performance.
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