1942-1947 Dodge WD20 Spark Plug Replacement Guide
Keep your classic Dodge truck running smoothly with the right spark plugs and essential maintenance tips.
- Use Champion brand copper core spark plugs; they are appropriate for the vehicle's original ignition system.
- Always check and set the spark plug gap to 0.025 inches before installation.
- Replacing spark plugs is a very easy, low-cost DIY job that can significantly improve engine performance and reliability.
- There are no modern recalls or TSBs for this part; issues are related to age and normal wear.
Signs of Failing Spark Plugs
On a vintage truck like the 1942-1947 Dodge WD20, you don't have a check engine light to warn you about problems. You have to pay close attention to how your truck drives, sounds, and feels. Worn-out or dirty spark plugs will give you clear signs that it's time for a change.
- Hard Starting: The engine cranks for a long time before it starts, or it might not start at all. This happens when the spark is too weak to ignite the fuel mixture properly.
- Rough Idle: When the truck is stopped, the engine sounds shaky and uneven. You might feel more vibration than usual through the steering wheel or the seat.
- Engine Misfires: While driving, you might feel a jerking or hesitation as one of the cylinders fails to fire correctly. This can be more noticeable when going up a hill or accelerating.
- Poor Fuel Economy: If you find yourself visiting the gas station more often, bad spark plugs could be causing inefficient combustion, which wastes fuel.
- Sluggish Acceleration: The truck feels weak and doesn't respond as quickly when you press the gas pedal.
Choosing the Right Aftermarket Spark Plug
For a vehicle from this era, the line between "OEM" and "aftermarket" is blurry. Champion was a common original equipment supplier for many American vehicles in the 1940s. An aftermarket Champion plug today is often made to the same basic design as the original.
Pro Tip: Stick with standard copper core plugs. The ignition system on your WD20 was designed for them. Modern platinum or iridium plugs are not necessary and may not perform well with the original ignition system.
Brand & Quality Assessment
Champion: This is the most widely recognized and appropriate brand for your vintage Dodge. Champion Copper Plus plugs are a reliable, cost-effective choice that maintains the original performance characteristics of your truck's engine. They are designed to work perfectly with the 6-volt or 12-volt systems found in these trucks. Given the simplicity and reliability of this choice, there is little reason to seek out other brands.
| Part Type | Price Range | Notes |
|---|---|---|
| New Aftermarket (Champion) | $3.70 - $4.69 | The most common and recommended option. |
| New OEM (NOS) | $20.00+ | "New Old Stock" plugs are rare, expensive, and not necessary for performance. |
| Shop Labor | $50 - $100 | Typically less than one hour of work. |
Known Issues, Recalls, and Service Bulletins
Due to the age of the 1942-1947 Dodge WD20, there are no official recalls or Technical Service Bulletins (TSBs) from the NHTSA or Dodge for spark plugs. Any issues you encounter will be related to normal wear and tear or the general effects of age on the ignition system. Common problems found by owners in forums are typically related to incorrect gapping or oil fouling, which points to other engine issues like worn piston rings, not a fault of the plug itself.
Frequently Asked Questions (FAQ)
What is the correct spark plug gap for my Dodge WD20?
The correct spark plug gap is critical for a strong spark. For the flathead six-cylinder engine in your WD20, the standard gap is 0.025 inches. Always verify this gap with a feeler gauge and adjust the new plugs before installation. Plugs can be handled roughly during shipping, so never assume they are correctly gapped out of the box.
How often should I change the spark plugs?
With today's cleaner fuels, spark plugs last longer than they did originally. A good practice for a vintage truck is to inspect the plugs annually and plan on replacing them every 10,000 to 15,000 miles, or whenever you notice performance issues like a rough idle or hard starting.
What tools do I need to change the spark plugs?
This is a very simple job. You will need a spark plug socket (typically 13/16" or 21mm), a ratchet with an extension, and a spark plug gapping tool/feeler gauge. Anti-seize compound for the plug threads is recommended but should be used very sparingly.
What can the condition of my old plugs tell me?
"Reading" your old spark plugs can give you valuable insight into your engine's health. A light tan or grayish-brown deposit indicates a healthy engine. Black, sooty plugs suggest a rich fuel mixture or weak spark. Oily deposits can mean internal engine wear, such as worn piston rings or valve guides, which may require more than just a plug change to fix.
Technical Specifications
OEM Part Numbers: Champion RJ12C
Thread Diameter: 14mm, Thread Reach: 9.5mm (3/8"), Hex Size: 21mm (13/16"), Seat Type: Flat Gasket, Recommended Gap: 0.025 inches.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.