The 5.7 HEMI uses eight 14mm spark plugs with a long reach, and replacements are typically iridium- or platinum-tipped plugs gapped around 0.040 inches. Common aftermarket options include NGK and Bosch, and OEM Mopar plugs are also suitable. Always verify the exact part number and gap for your specific year and model in the owner's manual or with a dealer.
Understanding the 5.7 HEMI spark plug needs
The 5.7L HEMI is a coil-on-plug, eight-cylinder engine. Each cylinder requires a single spark plug, so you’ll replace eight plugs during a typical service. The engine’s aluminum cylinder heads and ignition system place emphasis on selecting the correct heat range, reach, and gap to maintain reliable firing, fuel economy, and emissions performance. While many owners choose iridium- or platinum-tipped plugs for longevity, copper-core plugs can still be used as factory replacements on older builds. Always start with the OEM specification for your exact year and model.
Common spark plug options for the 5.7 HEMI
Below are the main categories you’ll encounter when selecting plugs for a 5.7 HEMI. This helps you navigate aftermarket choices and OEM replacements.
- Iridium-tipped plugs: Known for long life and stable performance, these are a popular choice for modern 5.7 engines. Examples you’ll see from manufacturers include NGK Iridium IX and Bosch Iridium.
- Platinum-tipped plugs: A durable option that often provides good performance with a longer service interval than copper cores, available from brands like NGK and Bosch.
- Copper-core plugs: A traditional, cost-effective option that can be used as a direct replacement in some applications, though they typically require more frequent service than iridium or platinum types.
- OEM/Mopar plugs: Direct-from-dealer replacements that mirror factory specifications for heat range, reach, and gap; these are a reliable baseline choice.
In practice, iridium- or platinum-tipped plugs are the most common recommendation for a 5.7 HEMI due to longevity and reliable cold/hot performance. Always confirm the exact heat range, reach, and gap for your specific model year before purchasing.
Choosing and installing spark plugs on a 5.7 HEMI
To ensure proper function and avoid damage, follow these guidelines when selecting and installing plugs on a 5.7 HEMI.
- Identify your vehicle year and model to confirm the correct heat range and plug reach; consult the owner's manual or a dealer service bulletin.
- Choose a plug type from reputable brands (iridium or platinum are common for modern 5.7 HEMIs) and consider OEM Mopar plugs if you want exact factory specifications.
- Set the electrode gap to 0.040 inches (1.0 mm) using a spark plug gauge, unless your chosen plug arrives pre-gapped differently.
- Torque each plug to the manufacturer’s specification for your engine (typically in the 11–15 ft-lbs range for 14mm plugs in aluminum heads); use a torque wrench to avoid overtightening.
- Do not apply anti-seize compound on modern spark plugs in aluminum heads; use dielectric grease on the boot terminals and ensure clean, dry threads.
- Inspect coil boots and wiring as you go; coil-on-plug systems can fail independently of plugs, so replace worn boots if needed.
After replacing the plugs, recheck for proper engine running, check for misfires, and clear any stored trouble codes if the vehicle has a diagnostic system. If you’re unsure about the exact specs for your year/model, consult the service manual or a qualified technician.
Summary
The 5.7 HEMI generally uses eight 14mm, long-reach spark plugs with a typical gap of around 0.040 inches. Iridium- or platinum-tipped plugs are common choices for modern engines, with OEM Mopar plugs as a reliable baseline. Always verify the exact heat range, reach, and gap for your specific year and model, and follow proper torque and installation practices to ensure reliable ignition and engine performance.