2020 Toyota Highlander Spark Plug Type & Gap Guide

The 2020 Toyota Highlander is a highly reliable midsize SUV, but keeping its dynamic powertrains running at peak efficiency requires timely maintenance—including spark plug replacement. Whether you are driving the standard 3.5L V6 or the hyper-efficient 2.5L 4-cylinder Hybrid, using the correct spark plugs with the precise gap and torque is non-negotiable. As an ASE-certified master technician, I've seen exactly what happens when the wrong plugs are installed.

Below is your complete guide to the spark plug specifications, replacement procedures, and torque values for your 2020 Toyota Highlander.

Quick reference

(Note: Toyota heavily relies on Denso as their OEM supplier. Motorcraft and ACDelco are not recommended for Toyota applications.)

Why the right plug matters

Modern Toyota engines utilize high-compression ratios and complex fuel delivery systems (like Toyota's D-4S direct and port injection). Using the exact specified heat range is critical; a plug that is too hot can cause pre-ignition and catastrophic engine damage, while a plug that is too cold will foul out and cause misfires.

Furthermore, electrode metal matters. The 2020 Highlander requires Iridium spark plugs. Iridium is significantly harder and more durable than platinum or traditional copper. Copper plugs will burn up within 15,000 miles in this ignition system, and platinum plugs will struggle to maintain a consistent spark under the high-voltage demands of Toyota's coil-on-plug architecture. Stick to OEM Denso or premium NGK laser iridium plugs.

How to gap a spark plug

Most iridium spark plugs come pre-gapped from the factory (typically around 0.031 inches for the 2020 Highlander). However, shipping and handling can sometimes alter this gap.

1. Measure gently: Use a wire-style gauge tool rather than a sliding coin-style gauge. Iridium center electrodes are incredibly brittle. Dragging a coin gauge across the tip can easily snap the fine wire electrode.
2. Adjusting: If the gap is too tight, use the bending tool on the gapper to apply a light bend to the ground strap. Never pry against the center iridium electrode itself. If the gap is too wide, gently tap the ground strap on a soft wooden workbench to close it slightly.

Replacement procedure tips

Replacing plugs on the 2020 Highlander involves a modern Coil-On-Plug (COP) system.

• The V6 Firewall Challenge: For the 3.5L V6, the front three plugs are fully exposed and take 10 minutes to change. The rear three, however, are tucked under the intake manifold cowl. You will need to remove the upper intake plenum (surge tank) to access the rear coil packs. Have a new intake manifold gasket ready before you start this job.
• The Anti-Seize Debate: Toyota/Denso spark plugs feature a special zinc/nickel coating on the threads. Because of this, Denso specifically recommends against using anti-seize compound. Adding anti-seize acts as a lubricant, which often leads to over-torquing the plugs and stripping the aluminum cylinder head.
• Dielectric Grease: Always apply a small dab of dielectric grease to the inside of the coil pack boots before reinstallation. This prevents moisture intrusion, prevents voltage leaks, and ensures the rubber boot won't bake onto the ceramic plug housing over the next 60k+ miles.

Known issues

While some platforms have notorious ignition flaws—such as the dreaded Ford 3-valve 2-piece plug breakage or GM 5.3 ionization-sensing coil failures—the 2020 Toyota Highlander’s ignition system is incredibly robust. You do not have to worry about broken plug shells or cracked porcelain during removal, provided you blow out the spark plug tubes with compressed air prior to removal to ensure no debris falls into the cylinders.

The most common "issue" owners face is simply sticker shock at the dealership for the 3.5L V6 labor time due to the intake manifold removal. However, with patience and the right tools, it is a straightforward job.

Need plugs replaced? Find a shop on Repairius.