What size socket for Hemi spark plugs?
The typical spark plug socket size for Hemi engines is 5/8 inch (16 mm). This size covers the vast majority of Hemi spark plugs, but some aftermarket plugs may use a larger 13/16 inch hex, so always verify the plug’s hex size before you buy or install.
Common socket sizes used on Hemi engines
Most Mopar Hemi spark plugs—across the 5.7L, 6.1L, and 6.4L families—use a 5/8 inch hex across flats. The standard socket to reach these plugs is a 5/8 inch deep-well spark plug socket, typically with a rubber insert to hold the plug securely and a long extension to clear headers or manifolds. Rare exceptions exist for certain aftermarket plugs that may use a 13/16 inch hex; when in doubt, check the plug manufacturer’s specifications.
Why the right size matters
Using the correct socket helps prevent rounding off the plug’s hex and reduces the risk of dropping or cross-threading. A deep-well design and a rubber insert are especially helpful in the tight confines around Hemi engines, where spark plugs sit near exhaust manifolds and other components.
Model-specific notes
While the 5/8 inch size is the practical default for most Hemis, there are variations across generations and aftermarket plugs. If you’re replacing plugs on a specific year and model, consult the service manual or the plug manufacturer to confirm the exact hex size and torque specification for your vehicle.
Summary
For most Hemi engines, using a 5/8 inch (16 mm) spark plug socket is the standard approach. Always verify the hex size on your chosen spark plugs, as some aftermarket options can require 13/16 inch. Pair the socket with a deep-well design, a rubber insert, and a long extension, and torque the plugs according to the manufacturer’s guidelines and the vehicle’s service manual.
What spark plugs are recommended for a 5.7 Hemi?
Recommended spark plugs for a 5.7 Hemi include NGK Iridium IX plugs (like part #92460 or #92145), OEM Mopar plugs, and Bosch double iridium plugs. Iridium plugs are often recommended for their performance and longevity, with an expected life of 60,000 to 100,000 miles. The correct gap is typically 0.0440.0440.044 inches.
Top recommendations
- NGK Iridium IX (or Laser Iridium): Frequently cited as a top choice for performance and long life, with some models rated for up to 100,000 miles.
- Part numbers: #92460 or #92145
- Mopar OEM: These are the original equipment manufacturer (OEM) plugs and are a direct, reliable replacement, often with a 100,000-mile lifespan.
- Part number: SP143877AB
- Bosch Double Iridium: Another high-quality iridium option that is also a common recommendation.
Other options
- Champion Copper Plus: A less expensive option, but with a shorter lifespan (around 15,000 miles).
- Champion Platinum: An alternative to copper, with a longer life (around 60,000 miles).
Important considerations
- Gap: The correct gap for most 5.7L Hemi engines is 0.0440.0440.044 inches.
- Quantity: The 5.7L Hemi has two spark plugs per cylinder, so you will need a set of 16 plugs.
- Anti-seize: It is recommended to apply a small amount of anti-seize to the spark plug threads before installation.
Can I use 9 16 instead of 14mm for spark plugs?
For the majority of plugs, you need a 5/8” or 16mm socket. Some Fords use 9/16″ plugs, some newer European and Asian vehicles use 14mm plugs, and there are a few applications that use 7/8″, 13/16″, ¾” or 18mm plugs. All spark plugs are 6 sided, except some BMW engines.
Do all 5.7 Hemis have 16 spark plugs?
How many spark plugs are there in a Hemi V8? All modern Chrysler Hemi engines use two spark plugs per cylinder for a total of 16 spark plugs. This includes engines built in 2003 and later, ranging from the 5.7 liter to the 6.2 liter Hellcat engine.
What size socket for 5.7 Hemi spark plugs?
A 5/8 inch spark plug socket is the correct size for a 5.7L Hemi engine. Some sources may also mention a 16mm socket as an alternative, but 5/8" is the most commonly cited size, especially for vehicles that use a 14mm thread spark plug. You will also need an extension and a torque wrench for the job.
This video shows how to change the spark plugs on a 5.7L Dodge Hemi: 59sMoonBuilt GarageYouTube · Aug 9, 2023
- Socket size: 5/8 inch.
- Spark plug thread: The 5.7L Hemi typically uses a 14mm thread spark plug.
- Other tools needed: An extension and a torque wrench are also required for installation.
