2018 Toyota Highlander Spark Plug Guide

Quick Reference: 2018 Toyota Highlander Spark Plugs

Why the Right Spark Plug Matters

Choosing the correct spark plug is critical for engine performance, fuel economy, and longevity. It's not just about finding a plug that fits; the engineering behind it matters. Key factors include the heat range and the electrode material.

• Heat Range: This determines how quickly the plug dissipates heat from the combustion chamber. A plug that is too "hot" (dissipates heat slowly) can lead to pre-ignition or detonation. A plug that is too "cold" (dissipates heat quickly) can develop carbon fouling, leading to misfires. The factory-specified heat range is essential for your Highlander’s sophisticated engine management system.

• Electrode Material: The 2018 Highlander engines use long-life Iridium spark plugs from the factory.

  • Iridium: An extremely hard, dense precious metal, iridium allows for a very fine-wire center electrode. This sharp point requires less voltage to create a spark, resulting in a more consistent and efficient spark event. The primary benefit is longevity, with replacement intervals often exceeding 100,000 miles.
  • Platinum: Another long-life material, often used for the ground electrode in conjunction with an iridium center. It offers excellent wear resistance but is slightly less durable than iridium.
  • Copper/Nickel: These are standard on older vehicles. They have a larger diameter electrode and wear out much faster, typically needing replacement every 30,000 miles. Using copper plugs in an engine designed for iridium will result in poor performance, reduced fuel economy, and a drastically shortened service life.

How to Gap a Spark Plug

Properly gapping a spark plug ensures the spark has the perfect distance to jump, creating the most effective ignition event. Most premium iridium plugs, like those for your Highlander, come pre-gapped. However, it's wise to verify the gap before installation, as they can be mishandled during shipping. The specified gap for both Highlander engines is 0.043 inches (1.1mm).

1. Use the Right Tool: A wire-style or feeler gauge is recommended for iridium and platinum plugs. Avoid the old "coin-style" disc gappers, as they can put pressure on the fine-wire electrode and damage it.
2. Measure Carefully: Slide the correct wire or feeler between the center and ground electrodes. It should have a slight drag, but not be too tight or too loose.
3. Adjust Gently: If adjustment is needed, do not pry against the center electrode. Instead, gently bend the ground electrode (the L-shaped piece extending over the center) toward or away from the center to close or open the gap. Make tiny adjustments and re-measure until it's perfect.

Replacement Procedure Tips for the 2018 Highlander

Both the 2.7L and 3.5L engines in the Highlander use a modern Coil-On-Plug (COP) ignition system, which eliminates the need for distributor caps, rotors, and spark plug wires.

• Coil-On-Plug Removal: Each spark plug has its own ignition coil sitting directly on top of it. These are typically held down by a single 10mm bolt. After removing the bolt, gently twist and pull the coil straight up to remove it. The rubber boot can sometimes stick to the spark plug, so a firm, steady pull is key. Avoid using tools to pry the coil off, as this can crack the plastic housing.

• The Anti-Seize Debate: Modern spark plugs from manufacturers like NGK and Denso have a special trivalent (zinc-chromate) plating that acts as its own anti-seize and release agent. Applying traditional anti-seize compound to these plugs can act as a lubricant, leading you to overtighten the plug. This can stretch the threads in the aluminum cylinder head or even break the plug. It is generally recommended not to use anti-seize on modern plated plugs. Always follow the plug manufacturer's specific instructions.

• Dielectric Grease: While anti-seize is often discouraged on the threads, applying a small amount of dielectric grease to the inside of the ignition coil boot is highly recommended. This grease prevents the boot from sticking to the new spark plug's ceramic insulator, seals out moisture to prevent corrosion, and makes future removal much easier.

Known Issues

The 2018 Toyota Highlander is not known for any specific, widespread issues related to spark plug replacement. Problems like the notorious Ford 3-valve Triton plug breakage (due to a two-piece shell design) or GM 5.3L ionization-sensing coil issues are not applicable to these Toyota engines. The design is straightforward and robust, making spark plug replacement a reliable maintenance task when performed with care.

Need plugs replaced? Find a shop on Repairius.