Whether you're maintaining your personal vehicle or a fleet, inspecting and replacing spark plugs at the right intervals keeps engines running efficiently.
Note
Always check your owner’s manual for the correct spark plug type and replacement intervals, as these vary by vehicle.
What to Expect
- Time Needed: 30-60 minutes
- Difficulty: Moderate
- Average Cost: $45
Source: 2025 Fleet Benchmark Report
What You’ll Need
New spark plugs (check owner’s manual for correct type and gap size)
Spark plug socket & ratchet wrench
Spark plug gap gauge
Torque wrench
Dielectric grease (optional)
Shop rags & gloves
How to Inspect and Replace Spark Plugs
Step 1: Locate the Spark Plugs
- Open the hood and find the spark plug wires or ignition coils on top of the engine.
- Some vehicles require removing a plastic engine cover to access the spark plugs.
Step 2: Remove the Old Spark Plugs
- Disconnect the ignition coil or spark plug wire from the first spark plug.
- Use a spark plug socket and ratchet wrench to carefully loosen and remove the plug.
- Inspect the old plug for carbon buildup, oil fouling, or excessive wear.
Pro-tip
If the old plug is covered in oil or heavily corroded, it could indicate a bigger engine issue that needs attention.
Step 3: Check & Adjust the New Spark Plug Gap
- Use a spark plug gap gauge to measure the gap between the electrode and ground strap.
- Adjust the gap if necessary to match manufacturer specifications.
Step 4: Install the New Spark Plug
- Thread the new spark plug into place by hand to avoid cross-threading.
- Tighten with a torque wrench to the manufacturer’s recommended specification.
- Apply a small amount of dielectric grease to the ignition coil boot before reconnecting it.
Step 5: Repeat for All Spark Plugs & Test the Engine
- Repeat the process for each remaining spark plug.
- Start the engine and listen for smooth idling and consistent performance.
Avoid These Common Mistakes
- Over-tightening or under-tightening the spark plugs. Improper torque can cause damage to the cylinder head or spark plug threads. Always use a torque wrench and follow manufacturer specifications.
- Skipping the gap check. Even pre-gapped spark plugs can shift during shipping. If the gap is incorrect, it can lead to misfires and poor performance.
- Mixing up spark plug wires. If you remove multiple wires at once without labeling them, you may reconnect them incorrectly, causing engine misfires. Always replace one plug at a time.
Track service histories across all fleet assets
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FAQs
How often should I replace my spark plugs?
Most spark plugs last 30,000 to 100,000 miles, depending on the type (copper, platinum, or iridium). Check your owner’s manual for the recommended interval.
What are the symptoms of bad spark plugs?
Common signs include rough idling, engine misfires, poor acceleration, decreased fuel efficiency, and trouble starting.
How much does it cost to replace spark plugs?
A DIY spark plug replacement costs $20 to $100, depending on the type. A professional service typically costs $100 to $250, including labor.
Can I replace my spark plugs myself?
Yes! As long as you have basic tools and follow the correct steps, replacing spark plugs is a manageable DIY task for most vehicle owners.
What happens if I don’t replace worn spark plugs?
Old spark plugs can cause misfires, increased fuel consumption, rough engine performance, and long-term damage to ignition coils and other components.
