A Guide to Selecting the Right Spark Plugs for Your 1938 DeSoto S-5
Keep your classic 228 cubic-inch flathead six-cylinder engine firing on all cylinders with the correct new spark plugs.
- Use standard copper-core spark plugs from a reputable brand like Champion; avoid modern iridium or platinum plugs.
- Always check and set the spark plug gap to 0.025 inches before installation for reliable performance.
- Be extremely careful when removing old spark plug wires, as they can be brittle and may break.
- The 1938 DeSoto S-5 uses a 228ci inline-six engine which requires six spark plugs.
Symptoms of Failing Spark Plugs
On a vintage vehicle like the 1938 DeSoto S-5, the signs of a spark plug problem are often very clear. Because the ignition system is simpler than in modern cars, it is more sensitive to the condition of the plugs. You might feel the engine stumble or shudder, a classic sign of a misfire. Other common symptoms include a rough idle, difficulty starting the engine, and a general lack of power or hesitation when you accelerate. You may also notice that the engine is running less efficiently than it used to.
Choosing the Right Aftermarket Spark Plug
For your DeSoto S-5's original ignition system, selecting the right type of spark plug is more important than just finding one that fits. The electrical systems on these classic cars were designed for a specific kind of plug.
Brand & Quality: Stick with the Classics
Champion is a brand that has been producing spark plugs for over a century and was a common original equipment supplier for vehicles of this era. Their standard copper core plugs are an excellent and appropriate choice for the S-5's flathead engine. These plugs are designed to work perfectly with the stock ignition system's voltage and heat characteristics. Avoid modern plugs made with precious metals like iridium or platinum; they are designed for high-energy ignition systems and may not perform well, potentially leading to fouling and a weak spark in your vintage engine.
Spark Plug Cost Comparison
| Part Type | Price Range (Set of 6) |
|---|---|
| New Aftermarket (Champion Copper) | $22 - $29 |
| New OEM | Not Available |
Warning: Brittle Spark Plug Wires
The spark plug wires and their insulators on a vehicle of this age can become extremely brittle. When removing the old wires from the spark plugs, they can easily crack or break. It is highly recommended to use a dedicated spark plug wire puller tool and twist gently before pulling to avoid damage.
Pro Tip: Always Check the Gap
New spark plugs are not always pre-gapped correctly for your specific engine. For the Chrysler flathead six, a spark plug gap of 0.025 inches is a widely recommended starting point. Always use a feeler gauge to verify and adjust the gap on each spark plug before you install it. An incorrect gap can cause misfires and poor performance.
Frequently Asked Questions (FAQ)
Do I need special high-performance plugs for my DeSoto?
No. In fact, it's best to avoid them. The original ignition system is designed for standard copper-core spark plugs. Brands like Champion provide reliable performance that is perfectly matched to your vehicle's needs.
How often should I change the spark plugs?
For a classic car that is not driven daily, it's a good practice to inspect the spark plugs annually or every few thousand miles. While modern fuels are cleaner, regular inspection helps you monitor the engine's health. Fouled plugs can be an early indicator of other issues.
What does it mean if my old spark plugs are covered in black soot?
Black, sooty deposits on a spark plug are known as carbon fouling. This can be caused by a fuel mixture that is too rich, too much engine idling, or a weak spark. It's a sign that your engine may need a tune-up to adjust the carburetor or check the ignition system.
Are there any recalls or technical service bulletins (TSBs) for the spark plugs on a 1938 DeSoto S-5?
No. Modern recall and TSB systems managed by agencies like the NHTSA do not contain data for vehicles from this era. All maintenance and repair information is based on original service manuals and the collective knowledge of classic car communities.
Technical Specifications
Engine: 228ci Inline-6 Quantity Required: 6 Plug Type: Standard Copper Core Thread Diameter: 14mm Thread Reach: 9.5mm Hex Size: 21mm 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.