Replacing worn spark plugs can greatly improve your engine’s performance and efficiency, and it can be done at home with basic hand tools.
Recommended spark plug replacement intervals can range from 30,000 miles to every 100,000 miles, and they vary widely by car manufacturer and spark plug metal types, and design.
You will need to follow the recommendations in your owner’s manual. It’s OK to upgrade, but never down grade from the manufactures factory requirements. Doing so will hinder performance and may cause issues related to sister components or the engine itself.
Spark plugs fire constantly and wear down over driving time, reducing their efficiency. Spark plug replacements can be challenging on some vehicles’ engines.
The greatest challenges you’ll face is accessibility and sticking components, such as when removing the spark plug wires or ignition coils/boots and unscrewing the spark plugs.
Some spark plugs can be difficult to reach and require the removal of the upper plenum/intake manifold. In these cases, a new plenum gasket will be needed. Check the Repair Guide for your specific vehicle and engine.
Why Replace Spark Plugs?
The primary reason for replacement is this: Your car has reached the spark plug replacement interval recommended by the manufacturer. You should be able to find this information in your owner’s manual.
On most cars today, the manufacturer requires plug replacement at around 100,000 miles, but it may be less for your car, so the owner’s manual should be your guide.
That said, this is stunning endurance considering not too many years back, plug replacement occurred as often as every 12,000 to 15,000 miles.
The second reason is that your car is acting up, and after some diagnostic homework, the spark plugs appear to be the culprits. Rough running, misfiring, difficulty starting, and/or an OBD II diagnostic code may direct you to the need for new spark plugs.
In general, any spark plug replacement job will require all the plugs to be replaced. Some engines will have one plug per cylinder, but there are cars on the road today running two spark plugs per cylinder.
If you are unsure of this, your dealer or parts store guy or gal can tell you how many you will need.
How Hard Is It to Replace Spark Plugs?
For the experienced DIY mechanic, any car’s plugs can be replaced. For the newcomer to automotive repair work, plug replacement may be a daunting task, and here’s why.
For most of today’s engine layouts, two problems may loom:
- The top of the engine and the plugs may be hidden beneath one or more covers, heat shield(s), numerous hoses, tied-down wiring bundles, and the underhood support structure.
- If the engine is cross-mounted and, in particular a V6, the rear cylinder head may be tucked against the firewall, making the plugs almost impossible to see.
For these situations, replacing the plugs must be preceded by relocating or removing the things that are in the way. And you may have to include the need to reach into a narrow space between the engine and firewall to access the plugs hidden there.
These steps can be the daunting part of the task. Not impossible, but worthy of consideration. You need to ask yourself, “Do I really want this challenge?”
How To Change Spark Plugs
#1. Gather The Necessary Tools.
Changing a spark plug requires at least the following tools:
- A special socket that is deep enough to accommodate the plug
- An interior rubber gasket that protects the tip of the plug from damage
- A spark-plug gapping tool to check the spacing between the electrode and the ground strap against your vehicle’s specifications
The most common spark plug socket sizes are 5/8 inch and 13/16 inch.
#2. Make Sure The Engine Is Cold.
A hot engine can burn your skin. On top of that, changing a spark plug with a warm engine head can damage the threads that hold it in place.
#3. Disconnect The Battery.
When working on any aspect of an engine’s electrical system, it’s always a good idea to disconnect the battery terminals to prevent accidental short circuits. If you don’t know how to do it properly, follow this article: How To Disconnect A Car Battery?.
#4. Remove Spark-Plug Wires Or Coil-On-Plug Connectors.
Older vehicles use spark-plug wires that connect them to the ignition system. Many newer models rely on a coil-on-plug design, which gives each individual spark plug its own ignition coil.
Regardless of the design of your vehicle, each must be removed prior to replacing your spark plugs.
Spark-plug wires are removed with a simple straight-up pulling motion, holding on to the boot that slips over the plug itself. Remember to label each wire to keep them in the correct order for reinstallation.
Coil-on-plug connectors often feature a locking tab that you may have to depress with a screwdriver in order to release before you’re able to pull the connectors off—be sure to label them carefully for reinstallation.
#5. Remove Spark Plug With the Socket.
Fit the spark plug socket over the protruding plug and gently unscrew it from the engine using a counter-clockwise motion.
Too much force can crack the plug and cause pieces to fall into the engine. Do your best to ensure no debris enters the spark plug hole when you lift it out.
#6. Examine The Spark Plug.
By determining the condition of the spark plug you’re changing out, you can gain insight into how your engine is performing and help diagnose any potential problems.
#7. Install New Spark Plug.
Thread a new spark plug into the cavity where you removed the old one, being careful not to cross-thread or force in the plug.
Screw it in until finger tight, then use your socket to give it another half-turn. With most brands of spark plugs, rubbing a little anti-seize lubricant on the threads can help ensure that the spark plugs will be easy to remove the next time.
#8. Reattach Wires / Coil-On-Plug Connectors / Battery.
Wrap up your installation by reinstalling the vehicle’s spark-plug wires or coil-on-plug connectors in the correct order, and then reconnect the battery.
Be sure and gather up all tools, and the engine is free and clear to start. Starting the engine after the spark plug replacement is a good way to validate your work.
FAQs.
What are the symptoms of a bad spark plug?
If the engine doesn’t seem to catch right away, that might be your first heads-up. It can also be a sign that the engine hesitates or doesn’t have the same pull from acceleration. Rough idling with engine misfires is another sure sign, along with greater fuel consumption.
Any or all of these symptoms suggest it’s time to have your spark plugs changed. Read our Car Advice article How Do I Know If My Spark Plugs Need Replacing? for a full overview, including additional signs it’s time to replace.
What’s the replacement cost for spark plugs?
Spark plugs generally cost less $10 each. The cost depends on the expected life and the material used on the electrode. Platinum- or iridium-tipped plugs using laser technology cost the most: as much as $25 each.
You can pay between $16 and $100 for a set of spark plugs, depending on the type of plugs you need and the number of cylinders your engine has. And when figuring out the price, it helps to remember that some specialty engines use two spark plugs per cylinder.
How often do I need to change my spark plugs?
In the past, experts recommended changing spark plugs every 30,000 miles or so. With today’s extended-life spark plugs, the life expectancy can go as high as 100,000 miles.
Checking and replacing the spark plugs is usually part of your vehicle’s routine service interval. Rarely do you need to make an appointment just for the spark plugs. Consult your Owner’s Manual for more details.
Do I need to replace my spark plug wires?
Usually, yes. You should replace the spark plug wires when you get new spark plugs. With standard spark plugs, that might be every 30,000-40,000 miles or so. If your vehicle uses extended-life spark plugs, you could go as long as 100,000 miles before changing the spark plug wires.
It’s still a good idea to regularly inspect the wires for any frays, cracks, and even bites (yes, bites!), since some wires are made from a soy-based material that’s a favorite snack for rodents.