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Kia Optima Engine Spark Plugs Replacement Guide
How to change the engine spark plugs in a 3rd generation 2011 to 2015 Kia Optima with the Theta II 2.4L I4 GDI motor.

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Paul B. Michaels
Author & Photographer
Auto Mechanic Since 1989

2013 Optima 2.4L I4
Pull Off Plastic Engine Cover
Underside of Engine Cover
This automotive maintenance tutorial was specifically written to assist owners of the third generation (2011, 2012, 2013, 2014 & 2015) Kia Optima sedan equipped with the Theta II 2.4 liter inline four cylinder GDI engine in checking or replacing the spark plugs.

Owners of other Hyundai or Kia vehicles with the Theta II 2.4L GDI I4 or 2.0L turbocharged engines such as the Sonata, Tucson, Santa Fe, Rondo, Cadenza, Sportage, Sorento, Genesis Coupe and ix35 may also find these DIY instructions to be helpful.

The OEM iridium tipped spark plugs in this 2013 Optima EX were Denso brand part number FXU16HR11 (3478).

Other compatible replacement spark plugs with their part numbers include the following: Champion REC12WMPB5 (9055), Autolite Iridium XP6203 and NGK Nickel # BR9EYA.

The tools and other items needed to complete this DIY procedure include a 10mm socket, a 1/4" drive ratcheting wrench, a 5/8" spark plug socket, a 6" extension bar, a 3/8" drive ratchet, a spark plug gap gauge, anti-seize lubricant (optional) and dielectric grease.

Hyundai Theta II GDI Motor
Grey Plastic Locking Tab
Pull Up Locking Tab
The first step is to pull off the plastic engine cover.

It is held in place by four friction fasteners on the underside that attach to metal pegs on the top of the engine.

If you have access to compressed air or a wet/dry shop vacuum, thoroughly clean off the top of the engine to help avoid having any debris fall in to the spark plug well.

I'd recommend checking or changing one spark plug at a time to further reduce the risk of having something fall in to the cylinder.

Pull the light grey plastic locking tab on the power connector away from the ignition coil to unlock it.

Press Tab - Pull Off Plug
Remove 10mm Bolt
10mm Bolt Removed
Press down on the release button and slide the electrical connector straight off the ignition coil.

Remove the bolt holding the ignition coil in place to the engine by turning it counter clockwise with the 10mm socket and ratcheting wrench. Set the screw aside in a safe place.

Rotate Ignition Coil
Pull Out Ignition Coil
Spark Plug In Well
Turn the ignition coil back and forth a few times to make sure that the rubber dust boot is not stuck to the old spark plug.

Pull the ignition coil straight up and out of the well. Set the coil aside in a safe place.


Loosen Counter Clockwise
Detach Wrench - Spin Out
Lift Out Old Spark Plug
Attach the 5/8" spark plug socket to the 6" extension bar and the 3/8" drive ratcheting wrench.

(Your spark plug socket should have a rubber insert or a strong magnet to securely hold the spark plug in place.)

Carefully lower the spark plug socket down in to the well and attach it to the old spark plug.

Gently loosen the old spark plug by rotating it counter clockwise.

Once the spark plug is loose, detach the ratcheting wrench from the extension bar and spin it out the rest of the way by hand.

If you can't loosen the old spark plug, do not use excessive force to avoid cracking the ceramic portion of the plug.

Spray a small amount of penetrating oil such as PB Blaster, Liquid Wrench or Kano Kroil and wait at least 15 minutes or more before attempting to loosen it again. If you don't have any penetrating oil, try spraying some WD-40 or warm up the engine for a few minutes to help expand the metal engine block.

Old Denso # 3478
Lower In New Spark Plug
Spin In Clockwise By Hand
Lift the old spark plug straight out of the well and detach it from the socket.

If the rubber insert from the socket is still stuck to the old spark plug, re-insert it back in to the socket.

Inspect the old spark plugs to determine if the engine is running properly.

If the end of the old spark plug looks ashy white, the plugs may have been exposed to high temperatures such as overheating or they are the incorrect heat range for your driving conditions or environment.

On the other hand, if the old spark plugs are dark grey or covered in black soot, the engine may be burning oil and should be checked by a professional mechanic.

I recommend buying the OEM spark plugs which are the Denso 3478 (also known as part number FXU16HR11).

If you have a spark plug gap gauge, check that the gap on the new spark plugs matches the manufacturer's specification which should be .044". If a new spark plug's gap is not correct, it may have been dropped or damaged in shipment and should be returned or exchanged for a new one.

An optional step is to apply a tiny amount of anti-seize lubricant to the upper metal threads of the new spark plug. This will make the plugs easier to take out if they are not changed again for another 100k miles. Do not get any of the anti-seize on the electrode tip at the bottom of the new spark plug. Some spark plug manufacturers recommend against using anti-seize since it can lead to over tightening.

If you do apply anti-seize to the threads of the new spark plug, less force will be necessary to tighten them.

Push the new spark plug in to the socket and make sure that it is securely in place.

Carefully lower the spark plug attached to the socket and 6" extension bar down in to the well. Spin it in by hand it in the clockwise direction until it stops.

Tighten New Spark Plug
Apply Dielectric Grease
Lower Ignition Coil
Attach the 3/8" drive ratcheting wrench to the extension bar and tighten the new spark plug in the clockwise direction to just barely past the point when you feel the crush wash collapse.

Do not over tighten the spark plugs to prevent from cracking the ceramic body or stripping the aluminum threads.

Double check that the new spark plug is tight before moving on to the next steps.

Apply a small amount of dielectric grease to the opening of the rubber dust boot at the bottom of the ignition coil. The dielectric grease will help keep out moisture and create a better electrical contact.

Lower the ignition coil down in to the well and over the tip of the new spark plug.

Rotate the coil back and forth a few times to evenly distribute the dielectric grease.

Spin In 10mm Bolt
Tighten 10mm Clockwise
Push On Engine Cover
Spin in the ignition coil bolt by hand and then tighten it in the clockwise direction to just past hand tight with the 10mm socket and ratcheting wrench.

Try to avoid over tightening the bolt to prevent from cracking the plastic ignition coil.

Push the power plug straight on to the ignition coil until it clicks securely in to place.

Push down the light grey locking tab on the electrical connector.

Line up the plastic engine cover and push it back down in to place.

For more, check out my other Kia Optima Repair & Maintenance Guides.

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