Choosing the Right Spark Plugs for Your 1966 GMC PB15 Series
Keep your classic GMC van running smoothly with the correct set of new spark plugs.
- Stick with standard copper-core spark plugs from brands like Autolite, Champion, NGK, or Denso for best results.
- Always check and adjust the spark plug gap before installation, even if the box says they are pre-gapped.
- Symptoms like rough idling, poor acceleration, and difficulty starting are strong indicators that it's time for new plugs.
- Replacing spark plugs is a simple, low-cost maintenance job you can easily do yourself in under an hour.
Signs of Failing Spark Plugs
When the spark plugs in your PB15 Series start to wear out, your engine's performance will suffer. The signs are usually easy to spot if you know what to look for. You might notice the engine is harder to start, especially on cold mornings. Other common symptoms include a rough idle, where the engine shakes or vibrates more than usual, and hesitation or stumbling when you accelerate. You may also see a drop in fuel mileage because unburned fuel is being wasted. In more serious cases, the engine might misfire, which feels like a sudden jolt or loss of power while driving.
Don't Ignore Bad Plugs
Continuing to drive with fouled or worn-out spark plugs can lead to bigger problems. Unburned fuel can damage the catalytic converter (if equipped on later models) and poor combustion can lead to carbon buildup inside the engine. It's a simple and inexpensive part to replace, so it's best to do it as soon as you notice symptoms.
Choosing the Right Aftermarket Spark Plug
For a vintage vehicle like the 1966 GMC PB15 Series, you don't need fancy, expensive spark plugs. The original ignition system was designed for standard, copper-core plugs. These plugs work perfectly and are very affordable. While brands like NGK and Denso are known for high quality, especially in modern or imported vehicles, traditional American brands like Autolite and Champion were original equipment for many vehicles of this era and are excellent choices. The most important factor is getting the correct plug with the right heat range and physical dimensions (thread reach and size) for your specific engine, which could be an inline-6 or a GMC V6.
Brand Quality Tiers
For this particular vehicle, the brands available are all reputable. The main difference is often in user preference and minor design variations.
- Good - Standard Replacement: Autolite and Champion are classic choices for American engines from the 1960s. They offer reliable performance at a very low cost and are often recommended for keeping things original. Many owners of similar-era GMC trucks stick with these brands.
- Better - High-Quality Standard: NGK and Denso are Japanese brands with a global reputation for excellent quality control and performance. They make standard copper plugs that are a great fit for the PB15 Series. Some owners of classic GMCs have reported smoother idling and better starts after switching to NGK plugs.
Check the Gap!
Even if a spark plug is listed as "pre-gapped," you must always check the gap with a feeler gauge before installation. The correct gap for your PB15's engine is critical for proper performance. An incorrect gap can cause misfires and poor fuel economy.
| Brand Tier | Brands | Estimated Price Range |
|---|---|---|
| Standard Replacement | Autolite, Champion | $3.50 - $6.00 |
| High-Quality Standard | NGK, Denso | $4.50 - $9.00 |
| Premium (Generally Not Needed) | Iridium/Platinum variants | $9.00 - $16.38+ |
Frequently Asked Questions (FAQ)
How often should I change the spark plugs on my 1966 PB15 Series?
For a classic vehicle with standard copper spark plugs, a good rule of thumb is to inspect them every year and replace them every 10,000 to 20,000 miles, or every 2-3 years, whichever comes first. Since these vehicles are often not driven daily, time can be as much a factor as mileage.
Do I need special tools to change my spark plugs?
You will need a basic ratchet set, a spark plug socket (which has a rubber insert to protect the plug), a spark plug gap gauge, and possibly a socket extension. These are common tools and the job is very straightforward on these engines.
Should I use platinum or iridium plugs for better performance?
It's generally not recommended. The ignition systems in 1960s vehicles were not designed for these modern plugs. Standard copper-core plugs provide the best performance for the original ignition system and are much more affordable.
What is the correct spark plug gap?
The correct gap can vary depending on the exact engine (inline-6 or V6) and any modifications. A common gap for these engines is between .035 and .040 inches. Always consult a service manual for your specific engine if possible.
Is there a difference between OEM and aftermarket spark plugs for this van?
The original OEM plug was likely an AC Delco. However, high-quality aftermarket brands like Autolite, Champion, NGK, and Denso meet or exceed original specifications. For a vehicle of this age, a new aftermarket plug from a reputable brand is a perfectly reliable and cost-effective choice.
Technical Specifications
OEM Part Numbers: ACDelco R45 ACDelco R45S ACDelco C44NS
Engine dependent. Could be a 14mm thread with either a 3/8" or 3/4" reach. It is critical to physically match the old plug's reach to the new one to avoid engine damage. Common cross-references include Champion J8C and NGK B6S.
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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.