Typically, expect to replace spark plugs around 100,000 miles if your 5.7 HEMI is equipped with iridium or platinum sparks; copper plugs usually require more frequent changes, roughly 30,000 to 60,000 miles. Always check your owner’s manual or consult your dealer for the exact interval for your model year and plug type.
In this guide, we break down the standard replacement intervals, signs that you should replace sooner, and a practical how-to for performing the job on a 5.7 L HEMI. The eight-cylinder HEMI uses one spark plug per cylinder and a coil-on-plug ignition design, which affects access and replacement steps. Driving conditions, maintenance history, and plug type all influence when you’ll need to replace them.
Understanding the 5.7 HEMI spark plugs
The 5.7 L HEMI is an eight-cylinder engine with one spark plug per cylinder and coil-on-plug ignition. Modern factory plugs are typically iridium or platinum long-life designs, designed to last longer than older copper plugs. Depending on your model year, you may have different spark plug brands or part numbers, but the replacement approach—removing each coil, pulling the old plug, and installing a new one—remains consistent. Always verify the recommended plug type and gap specification for your exact vehicle.
Plug count and ignition design
There are eight spark plugs—one for each cylinder—paired with coil-on-plug ignition. This arrangement simplifies timing and ignition but can make access for replacement more straightforward on top of the engine, though some models may require minor disassembly to reach the deepest plugs.
Plug type and longevity
Factory plugs in many 5.7 HEMIs are designed for long service life, typically iridium or platinum. These materials are more durable and maintain electrode shape longer, which is why the common guidance tends toward a 100,000-mile replacement interval under normal driving. If your vehicle uses copper plugs, the interval will be much shorter, generally 30,000–60,000 miles.
Recommended replacement intervals
Before listing the intervals, note that the exact mileage can vary by plug type, model year, and driving conditions. The following guidance reflects common industry practice for the 5.7 HEMI.
- Copper spark plugs: typically 30,000–60,000 miles, depending on driving habits and conditions. If you’re using copper plugs, expect more frequent changes.
- Platinum or iridium spark plugs: commonly up to 100,000 miles under normal driving. Extreme conditions (towing, frequent short trips, high heat) may shorten this interval.
- Always follow the owner’s manual or a dealer’s recommendation for your exact vehicle, as intervals can vary by year and plug type.
In practice, most drivers with modern iridium or platinum plugs in a 5.7 HEMI won’t need a plug change until around the 100,000-mile mark under standard use, but severe service or early signs can shorten that window.
When to replace sooner: signs and service considerations
Even with long-life plugs, wear or fault conditions can necessitate earlier replacement. Watch for these indicators and act when you notice them.
- Misfiring or rough idle, especially at idle or during acceleration.
- Loss of power or sluggish acceleration, along with a drop in fuel economy.
- Illumination of the check engine light with misfire-related trouble codes (e.g., P0300 series).
- Difficulty starting or longer cranking times, especially in cold weather.
- Visible wear on plugs or electrode erosion during inspection.
- Engine running rough or vibrating due to worn ignition components (coils/wires) that may coexist with plug wear.
If you notice any of these symptoms, have the ignition system inspected and consider replacing plugs as part of a broader diagnostic or maintenance service.
How to replace spark plugs on a 5.7 HEMI
Replacing spark plugs on a 5.7 HEMI is a doable task for a confident DIYer, but it requires careful handling of ignition coils and correct torque. The following steps assume coil-on-plug ignition and typical factory plugs. If you’re unsure, a professional shop can perform the service quickly and correctly.
- Park the vehicle on a level surface and disconnect the negative battery cable. Let the engine cool fully to avoid burns and thread damage.
- Remove any engine covers or intake components that may block access to the spark plugs, following the factory manual.
- Locate the ignition coil for the first cylinder. Disconnect the electrical connector, then remove the coil mounting bolt and lift the coil away from the spark plug.
- Carefully remove the old spark plug with a spark plug socket attached to a long extension. Use a swivel-extendable adapter if needed to reach deeper plugs.
- Check the spark plug gap on the new plug if it isn’t pre-gapped to the manufacturer’s specification. For iridium/platinum plugs, gaps are often pre-set; verify before installation.
- Thread the new plug by hand to avoid cross-threading, then tighten it to the manufacturer’s specified torque (typically around 11–15 ft-lbs, or 15–20 Nm, but always confirm with the service manual for your exact plug and model year).
- Reinstall the ignition coil, reconnect the electrical connector, and move on to the next cylinder. Repeat steps 3–7 for all eight cylinders.
- Reassemble any engine covers or intake components you removed. Reconnect the negative battery cable.
- Start the engine and listen for smooth operation. If codes were present, clear them if necessary and verify that the check engine light remains off after a short drive.
Using the factory-recommended plug type and torque is essential for optimal performance and avoiding thread damage. If in doubt, seek professional assistance.
Summary
For most 5.7 HEMI engines, iridium or platinum spark plugs are designed to last about 100,000 miles under normal driving, with copper plugs requiring more frequent changes around 30,000–60,000 miles. Monitor for signs of wear or misfire, and consider replacement sooner if you tow, drive in extreme heat, or take many short trips. When replacing, follow the coil-on-plug access steps and torque specifications from your vehicle’s manual. Regular maintenance and timely replacement keep the 5.7 HEMI running smoothly and efficiently.