2016–2020 Kia Optima
By Ray Delgado ✓ Certified Mechanic · Published Sep 21, 2026 · Updated Oct 22, 2026
Save $204 by doing it yourself! Shop cost: $260
Quick answer: Spark Plug Replacement on a 2016–2020 Kia Optima is rated Advanced and takes about 60-90 minutes. You'll need 6 tools for this job, and parts cost about $56. This guide walks you through the full job step by step, including the mistakes to avoid.
| Part Name | Part Number | Price | Buy |
|---|---|---|---|
| Iridium spark plugs for Kia Optima (verify engine and heat range) | — | $48.00 | |
| Spark plug boot grease (small tube) | — | $8.00 |
About prices: shown prices are typical retail averages and change frequently; cheaper alternatives may be available. Confirm the current price before buying.
💡 Pro tip: Order all parts at once to save on shipping
Follow these steps carefully
Confirm your 2016-2020 Kia Optima has the 2.4L Theta II GDI four-cylinder — the 1.6T and 2.0T take different plugs. The 2.4L takes four NGK SILZKR7B11 Laser Iridium plugs (stock 9723), pre-gapped to 0.044 inches. Scan for misfire codes (P0300-P0304) first and note the cylinder.
Remove the plastic engine cover to expose the four coil-on-plug units in a row along the top of the valve cover, and unclip the air intake duct if it overhangs the coils. Disconnect the negative battery terminal with a 10mm wrench.
Press the release tab on each coil connector and unplug it, remove the 10mm coil hold-down bolts, and pull each coil straight up — give each a gentle twist first to break the boot's seal on the plug, since the boots bond with heat over time. Keep the four coils in order on a clean rag. On the 2016-2020 Kia Optima, blow each plug well out with compressed air before loosening a plug — the deep wells collect grit under the engine cover that will fall straight into the cylinder. Cover each open well with a rag as you go.
I learned this the hard way: Press the release tab on each coil connector and unplug it, remove the 10mm coil hold-down bolts, and pull each coil straight up
Loosen each old plug with a 5/8-inch (16mm) spark plug socket and a 6-inch extension, keeping the socket straight in the deep wells, and compare each new NGK SILZKR7B11 to the old plug: same 12mm thread, reach and heat range. The new plugs come pre-gapped to 0.044 inches — verify with a wire gauge but never pry on the fine iridium tip; discard any plug that arrives out of spec. Thread each plug in by hand for several full turns until the gasket seats, then torque to the spec in your owner's manual. Install them dry: NGK's trivalent thread plating needs no anti-seize, which would corrupt the torque reading.
I keep a mental note on this one: The new plugs come pre-gapped to 0.044 inches — verify with a wire gauge but never pry on the fine iridium tip; discard any plug that arrives out of spec.
Apply a thin film of dielectric grease inside each coil boot only — rubber, never the plug — to seal out moisture and ease the next removal. Push each coil firmly onto its plug, torque the 10mm hold-down bolts snug, and reconnect every locking-tab connector with a click. Refit the intake duct and engine cover, reconnect the negative battery terminal, and start the 2016-2020 Kia Optima. Confirm a smooth idle with no check-engine light and take it for a drive; a misfire code that returns on one cylinder points to that cylinder's coil pack, not the new plugs.
I've watched people get this wrong: Apply a thin film of dielectric grease inside each coil boot only — rubber, never the plug — to seal out moisture and ease the next removal.
Test your repair before closing everything up. If something doesn't work right, double-check your steps.
⚠️ Common Mistakes to Avoid
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