2018 Mercedes-Benz Metris Spark Plug Type & Gap

Quick reference

Why the right plug matters

Choosing the correct spark plug for your 2018 Mercedes-Benz Metris is crucial for optimal engine performance, fuel efficiency, and longevity. Spark plugs are a critical component of your ignition system, responsible for igniting the air-fuel mixture in your engine's combustion chambers.

Heat Range

Spark plugs are designed with a specific "heat range," which refers to their ability to dissipate heat. A plug that's too hot can lead to pre-ignition and detonation, causing engine damage. A plug that's too cold can lead to fouling, where carbon deposits build up on the plug, hindering its ability to spark effectively. The OEM-specified plug for your Metris's 2.0L M274 engine is engineered with the precise heat range for its operating conditions.

Electrode Metal

Modern spark plugs utilize various electrode materials, each with its own advantages:

• Iridium: These plugs offer the longest lifespan and best performance due to iridium's extreme hardness and high melting point. They typically feature a very fine center electrode, promoting a more focused and powerful spark. The NGK PLKER7A8EGS, which is the OEM plug, is an iridium-tipped plug.
• Platinum: Platinum plugs also provide excellent durability and a long service life, though generally not as long as iridium. They often have a platinum pad on the center and/or ground electrode.
• Copper: While copper is an excellent conductor, it's a softer metal, so copper plugs have a shorter lifespan. They are typically found in older vehicles or those with less demanding ignition systems. They are not recommended for your Metris.

How to gap a spark plug

While many modern iridium spark plugs come pre-gapped and it's generally advised not to re-gap them due to the delicate nature of the fine iridium tip, it's still important to understand the process. Always check the gap of any new plug against the manufacturer's specification (0.032 in / 0.8 mm for your Metris).

If you need to adjust the gap on a non-iridium plug (or if an iridium plug is slightly off and you proceed with extreme caution):

1. Use a wire-style gap gauge: Never use a flat, ramp-style gauge, as this can damage the electrode. A wire gauge allows you to accurately measure the distance between the center and ground electrodes.
2. Adjusting the gap: If the gap is too small, gently bend the ground electrode away from the center electrode using the gapping tool. If the gap is too wide, gently tap the ground electrode on a solid surface to close the gap. Always make small, precise adjustments.
3. Re-check: Re-check the gap after each adjustment until it matches the specification.

Replacement procedure tips

Replacing spark plugs on your 2018 Mercedes-Benz Metris with the 2.0L M274 engine is a straightforward process for the DIY mechanic, but a few tips can make it smoother:

• Coil-on-plug removal: Your Metris utilizes a coil-on-plug ignition system. To access the spark plugs, you'll first need to disconnect the electrical connector from each ignition coil and then unbolt and remove the coil. Be gentle when pulling the coils to avoid damaging the boot or the coil itself.
• Anti-seize debate: There's ongoing debate regarding the use of anti-seize compound on spark plug threads. Mercedes-Benz generally recommends against it, as the plugs supplied are typically coated to prevent seizing. Additionally, anti-seize can act as an electrical insulator and alter torque readings, potentially leading to over-tightening. Follow the manufacturer's guidelines, which for your Metris, means installing the plugs clean and dry.
• Dielectric grease on boots: Apply a small amount of dielectric grease to the inside of the ignition coil boots before reinstallation. This helps to seal out moisture, prevents the boots from sticking to the spark plugs, and aids in electrical insulation, ensuring a good connection.
• Torque Spec: Always adhere to the specified torque (15-18 lb-ft / 20-24 Nm). Over-tightening can damage the spark plug and cylinder head threads, while under-tightening can lead to combustion pressure leaks and misfires.

Known issues

The 2.0L M274 engine found in the 2018 Mercedes-Benz Metris is generally reliable, and there are no widespread, specific spark plug-related "known issues" similar to the Ford 3-valve two-piece spark plug breakage or GM's ionization-sensing coil problems. However, it's always good practice to inspect the removed spark plugs for signs of abnormal wear, which can indicate other engine issues.

Need plugs replaced? Find a shop on Repairius.