Choosing and Replacing Spark Plugs for Your 1966-1972 Citroen D21
Keep your classic Citroen's unique engine firing smoothly with the right set of new spark plugs.
- Standard copper spark plugs from brands like NGK or Champion are an excellent and affordable choice for the D21's original ignition system.
- Always verify the spark plug gap is correct (0.6mm-0.8mm) before installation to prevent misfires.
- Be careful not to over-tighten plugs in the aluminum cylinder head to avoid stripping the threads.
- Symptoms of failure include rough idle, engine misfires, hard starting, and decreased fuel mileage.
Symptoms of Failing Spark Plugs
Worn or faulty spark plugs can cause several noticeable problems in your D21. If you experience a rough idle, where the engine shakes or sputters when stopped, it could be a sign of a bad plug. You might also notice the engine hesitating or misfiring during acceleration. Difficulty starting the car, especially when the engine is cold, is another common symptom. Finally, a decrease in fuel economy can indicate that your spark plugs are no longer firing efficiently.
Known Issues for the Citroen D21
While no specific recalls or Technical Service Bulletins (TSBs) for spark plugs exist for this classic vehicle in the NHTSA database, owners on forums report some common issues. A frequent problem is running-on or "dieseling," where the engine continues to sputter after being turned off; this can sometimes be related to using spark plugs of the wrong heat range. Also, be aware that the aluminum cylinder head is susceptible to stripped threads if plugs are over-tightened or cross-threaded during installation. Always thread new plugs by hand to ensure they are seated correctly before using a wrench.
Choosing the Right Aftermarket Spark Plug
For a classic car like the Citroen D21, you don't need expensive, exotic spark plugs. Standard copper plugs are often the best choice as they are what the ignition system was originally designed for. All three available brands—Autolite, Champion, and NGK—offer suitable options.
Brand Quality Assessment
- NGK: Generally considered a top-tier choice for reliability and quality by mechanics and classic car owners. They offer standard copper plugs like the BP6HS and BPR6HS that are listed as compatible with the D21 engine. Some owners choose to upgrade to NGK Iridium plugs for claims of better starting and a more stable idle, but this is not essential.
- Champion: A traditional American brand that was original equipment for many classic cars. They offer dependable, OE-type replacement copper plugs like the L87YC that are a good fit for the D21. Some classic vehicle enthusiasts have noted that Champion plugs can be more prone to fouling in low-compression engines during light use compared to other brands.
- Autolite: Known for providing good value, Autolite is another reliable option. They produce standard copper plugs that are compatible with the 1966-1972 D21. While quality is generally good, some mechanics feel that consistency can be less precise than NGK.
Check the Gap
Always check the spark plug gap before installation, even if the box says they are "pre-gapped." The correct gap for a Citroen D21 is typically between 0.6mm and 0.8mm (0.025" - 0.032"). An incorrect gap can lead to misfires and poor performance.
Cost of New Aftermarket Spark Plugs (1966-1972 Citroen D21)
| Brand Tier | Example Brands | Price Range (Per Plug) |
|---|---|---|
| Good (Standard Copper) | Autolite, Champion | $3.68 - $4.98 |
| Better (Premium Copper/Platinum) | NGK (Standard, G-Power) | $6.99 - $9.97 |
| Best (Iridium) | NGK (Iridium IX) | $9.97 - $14.32 |
Frequently Asked Questions
How often should I replace the spark plugs on my D21?
For standard copper spark plugs used in a classic car like the D21, a good interval is every 10,000 to 20,000 miles or every few years, depending on use. Regular inspection and replacement will keep the engine running reliably.
Do I need special tools to change the spark plugs?
You will need a spark plug wrench, which is a deep socket designed specifically for this job. A 21mm or 13/16" socket is typically required. It's also helpful to have a socket extension and a way to clean debris from around the spark plug holes before removing the old plugs.
What is a spark plug's "heat range"?
The heat range refers to how quickly the spark plug tip dissipates heat. A "hot" plug stays hotter to burn off carbon deposits, while a "cold" plug runs cooler to prevent pre-ignition in high-performance engines. For a stock D21, using the standard, manufacturer-recommended heat range is crucial to avoid issues like engine run-on.
Can I use modern iridium or platinum plugs in my D21?
Yes, you can use modern plugs like NGK's Iridium IX series. They may offer benefits like a longer lifespan and more stable idle. However, the original ignition system was designed for standard copper plugs, which are more than adequate and often the most cost-effective choice.
Technical Specifications
Thread Size: M14x1.25; Wrench/Hex Size: 21mm (13/16"); Thread Length: 12.7mm (0.5"); Recommended Gap: 0.6mm - 0.8mm (0.025" - 0.032").
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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.