2018 Ford Explorer Spark Plug Replacement — 2.3L & 3.5L EcoBoost

I've done plugs on both versions of the 2018 Ford Explorer, and both jobs are very doable in a home garage with basic tools. The 2.3L EcoBoost is the easier job — all 4 plugs accessible from the top. The 3.5L EcoBoost twin-turbo is more involved, especially the rear cylinder bank, but still a DIY job if you take your time. Here's exactly how I approach both.

Which Engine Do You Have?

• 2.3L EcoBoost I-4 — Standard Explorers, XLT and some Sport trims. A turbocharged 4-cylinder with 280 hp.
• 3.5L EcoBoost V6 — Sport and Platinum trims, and the Police Interceptor. Twin-turbocharged V6 with 365–400 hp.

The 3.5L TiVCT (naturally aspirated) is a different engine not covered here; it uses a different plug and procedure.

Parts and Specs

2.3L EcoBoost (4 plugs)

Item	Spec
Spark plug	Motorcraft SP-556
Gap	Pre-gapped at 0.035" (0.89 mm)
Torque	9 ft-lb (12 Nm) / 108 in-lb
Interval	60,000 miles
Thread size	M12 × 1.25

3.5L EcoBoost (6 plugs)

Item	Spec
Spark plug	Motorcraft SP-537
Gap	Pre-gapped at 0.036" (0.90 mm)
Torque	9 ft-lb (12 Nm) / 108 in-lb
Interval	60,000 miles
Thread size	M14 × 1.25

Always use Motorcraft plugs in Ford EcoBoost engines. The platinum/iridium tip geometry on the Motorcraft plugs is matched to the EcoBoost combustion chamber. Aftermarket "equivalent" plugs have documented fitment and performance issues in EcoBoost applications.

Tools

• 3/8" drive ratchet
• 5/8" spark plug socket (2.3L) or 9/16" spark plug socket (3.5L)
• 3" and 6" extensions
• Universal joint / swivel adapter (essential for 3.5L rear bank)
• Torque wrench (in-lb scale, or ft-lb wrench that reads accurately at 9 ft-lb)
• Dielectric grease
• Compressed air

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2.3L EcoBoost — Step-by-Step

The 2.3L EcoBoost sits longitudinally in the engine bay with the intake facing the firewall. All 4 coil-on-plug units are accessible from the top.

1. Let the engine cool completely — at least 2 hours after last run.

2. Remove the plastic engine cover (held by 4 push-clips on most '18 Explorers).

3. Locate the 4 COP units on top of the engine. Disconnect the electrical connector on each by pressing the tab and pulling straight back.

4. Each COP is held by a single 8mm bolt. Remove all 4 bolts and pull each COP straight up. Twist gently if stuck.

5. Blow compressed air into each plug well before removing the plugs. Any debris in the well will fall into the cylinder if you skip this.

6. Use the 5/8" plug socket with a 6" extension. Break each plug loose (counterclockwise), then spin out by hand.

7. Install new SP-556 plugs. These are pre-gapped — do not adjust. Thread in by hand until snug, then torque to 9 ft-lb (108 in-lb). The aluminum cylinder head strips easily if you over-torque; use a torque wrench.

8. Apply a small amount of dielectric grease inside each COP boot. Reinstall COPs and snug the 8mm bolts.

9. Reconnect all 4 electrical connectors.

10. Reinstall the engine cover and start the engine. A rough idle for 10–15 seconds is normal as the new plugs seat.

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3.5L EcoBoost — Step-by-Step

The 3.5L EcoBoost is a transversely-mounted V6 in the Explorer. The front bank (3 cylinders facing the radiator) is easy. The rear bank (3 cylinders facing the firewall) is the challenge.

Front Bank (Cylinders 1, 2, 3)

1. Remove the plastic engine cover.

2. Disconnect and remove the 3 front COP units using the same process as above — electrical connector, 8mm bolt, straight pull.

3. Blow out plug wells with compressed air.

4. Use the 9/16" socket with a 3" extension. Remove all 3 front plugs.

5. Install new SP-537 plugs. Gap to 0.036" if not confirmed pre-gapped. Hand-thread, then torque to 9 ft-lb.

6. Reinstall front COPs with dielectric grease in each boot.

Rear Bank (Cylinders 4, 5, 6)

7. The rear 3 cylinders face the firewall — there is minimal clearance between the engine and the firewall. This is where the universal joint / swivel adapter earns its place in your toolbox.

8. From the top, disconnect the 3 rear COP connectors. Remove the 8mm hold-down bolts.

9. To pull the rear COPs, you may need to access from the side — some mechanics find it easier to reach in from the passenger-side fender with a long arm. The COPs twist and pull straight up once the bolt is out.

10. Blow out the plug wells with compressed air via a long straw attachment.

11. Use the 9/16" socket + 6" extension + swivel joint. Break each rear plug loose from the top working blind, or use an inspection mirror to confirm socket seating before breaking torque.

12. Remove the old plugs. Install new SP-537 plugs hand-tight, then torque to 9 ft-lb using the same extension + swivel combination.

13. Reinstall rear COPs with dielectric grease, reconnect connectors, and reinstall the engine cover.

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Common Mistakes

1. Using non-Motorcraft plugs. The EcoBoost combustion geometry is tuned to Ford's OEM plug design. Aftermarket plugs (even "equivalent" iridium plugs) have caused misfires and accelerated wear in 3.5L EcoBoost applications.

2. Torquing to 20+ ft-lb. These are aluminum heads with platinum-tipped plugs. 9 ft-lb is the spec. It feels underwhelmingly light — trust the torque wrench.

3. Skipping the compressed air step on the rear bank. The rear cylinder wells on the 3.5L collect carbon debris because the coil boots sit loosely over time. Debris in a cylinder on a turbocharged engine causes serious damage.

4. Forgetting the dielectric grease. On the EcoBoost, the coil boots can stick to the plugs due to heat cycling. You'll find this out the hard way at the next plug change when you're fighting stuck boots off 60,000-mile-old plugs.

5. Not checking the gap. The SP-537 is often listed as "pre-gapped" but transport vibration can close the gap slightly. Verify every plug.

The 2017 Ford F-150 spark plug replacement guide covers the same EcoBoost plug procedure for the F-150's 2.7L and 3.5L variants if you're also servicing a truck. For Explorer-specific maintenance, the 2018 Ford Explorer coolant flush is the next logical service if you're working through the maintenance schedule.

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