A Guide to Spark Plugs for the 1937-1950 Chrysler Imperial
Keep your classic Imperial's straight-eight engine running smoothly with the right set of spark plugs.
- For a 1937-1950 Imperial, modern Champion Copper Plus spark plugs are a reliable and appropriate choice.
- You must manually set the spark plug gap. Use .025" for 1937-1948 models and .035" for 1949-1950 models.
- Symptoms of failure include rough idle, difficult starting, and poor acceleration.
- Replacing all eight spark plugs is a simple, low-cost maintenance task that you can likely do yourself in under an hour.
Signs of Failing Spark Plugs in Your Imperial
Worn or fouled spark plugs can cause a number of noticeable issues. Because these engines are from a different era, the symptoms might be more pronounced than in a modern car. You'll want to look out for a few key signs that it's time for a replacement.
- Rough Idle: If your Imperial's engine shakes, sputters, or sounds uneven when stopped, failing spark plugs are a likely cause. A weak or inconsistent spark in one or more cylinders disrupts the engine's balance.
- Difficulty Starting: While a 6-volt electrical system can sometimes present challenges, worn spark plugs make it even harder for the engine to fire up, especially when cold. A strong spark is needed to get the combustion process started reliably.
- Reduced Power and Poor Acceleration: If your car feels sluggish or hesitant when you press the accelerator, it may be due to misfires caused by bad plugs. With eight cylinders, the loss of one or two might be subtle at first but will impact overall performance.
- Worse Fuel Economy: Inefficient combustion from old plugs means you're not getting the most power out of your fuel, leading to more frequent stops at the gas station.
No Check Engine Light
Unlike modern vehicles, your 1937-1950 Imperial does not have an onboard computer or a "Check Engine" light to warn you about failing spark plugs. You must rely on observing the engine's performance and sound.
Choosing the Right Aftermarket Spark Plugs
For a vehicle as special as the 1937-1950 Imperial, finding "new old stock" (NOS) OEM parts is rare and often expensive. Fortunately, modern aftermarket manufacturers like Champion produce high-quality spark plugs that are excellent replacements. Champion was a common original equipment supplier, and their modern copper plugs are very well-suited for these engines.
Champion Copper Plus
The Champion Copper Plus series is a reliable and cost-effective choice. These plugs use a copper core, which helps control heat and provides reliable performance. For the Imperial's straight-eight engine, a standard copper plug provides the consistent spark needed for smooth operation. There is no performance benefit to using more expensive platinum or iridium plugs in this type of vintage engine; in fact, standard copper plugs are often recommended.
Always Check the Gap
Even if new spark plugs are advertised as "pre-gapped," you must check and adjust the gap for your specific vehicle. For 1937-1948 Imperials, the recommended spark plug gap is .025 inches. For 1949-1950 models, it is .035 inches. Use a wire-style feeler gauge for accuracy.
Cost to Replace Spark Plugs on a 1937-1950 Chrysler Imperial
Replacing the spark plugs is one of the more affordable maintenance jobs for your classic car. The primary cost is the parts themselves, as labor is relatively straightforward.
| Item | Estimated Cost |
|---|---|
| New Aftermarket Spark Plugs (Set of 8) | $29 - $38 |
| Shop Labor | $50 - $150 |
| Total Estimated Cost | $79 - $188 |
Frequently Asked Questions
How often should I change the spark plugs on my Imperial?
For vintage cars using standard copper spark plugs, a good interval is every 10,000 to 20,000 miles or every few years, depending on how much you drive. Given the age of the vehicle, regular inspection is more important than mileage alone.
Is it difficult to replace the spark plugs myself?
No, this is a very feasible DIY job for most owners. The spark plugs on the straight-eight engine are generally easy to access. You will need a spark plug socket, a ratchet, and a gap gauge. The entire process for all eight plugs should take less than an hour.
Should I use anti-seize on the new spark plug threads?
Yes, it is a good practice, especially with cast iron cylinder heads. Applying a small amount of anti-seize compound to the plug threads helps prevent them from getting stuck, making future removal much easier. Be careful not to get any on the electrode.
What about spark plug wires?
When replacing your spark plugs, it's a great time to inspect the spark plug wires. If they are original, cracked, or brittle, they should be replaced. Bad wires can cause a weak spark even with new plugs. Chrysler originally specified non-resistor plugs with resistor wires.
Technical Specifications
Spark Plug Gap (1937-1948): 0.025 inches. Spark Plug Gap (1949-1950): 0.035 inches. Engine requires 8 spark plugs.
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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.