Choosing the Right Spark Plugs for Your 1979-1986 GMC P3500
Keep your workhorse running strong with the correct spark plugs for your V8 engine.
- Stick with standard copper core spark plugs from reputable brands like ACDelco, NGK, or Autolite for the best performance in these vintage engines.
- Expensive iridium or platinum plugs are not necessary and may not provide any benefit.
- Always check and adjust the spark plug gap before installation; a common gap for the 5.7L V8 is .035 inches.
- Accessing the rear plugs can be challenging due to the van's engine 'doghouse', so be prepared with extensions and a universal joint.
Signs of Failing Spark Plugs
Worn-out spark plugs can cause noticeable problems in your P3500. Because these are heavy-duty vehicles, you might feel these symptoms more, especially under load.
- Rough Idle: The engine may shake or vibrate more than usual when you're stopped.
- Engine Misfires: You might feel a hesitation or stumble during acceleration.
- Poor Fuel Economy: If you're filling up the tank more often, bad plugs could be the cause.
- Difficulty Starting: A weak spark makes it harder for the engine to fire up, especially when cold.
- Reduced Power: Your van may feel sluggish and struggle to haul heavy loads or get up to speed.
Choosing the Right Aftermarket Spark Plug
For the big V8 engines in the 1979-1986 P3500, like the 5.7L 350 or the 7.4L 454, you don't need the most expensive, high-tech spark plugs. In fact, these older engine designs run best on traditional copper core plugs. They provide a strong spark and handle heat well for this application. While platinum or iridium plugs are available, they are often not necessary and can sometimes cause issues.
Brand Quality Tiers
| Tier | Brands | Description |
|---|---|---|
| OEM & Premium Aftermarket | ACDelco, NGK | ACDelco is the original factory brand for your GMC and a very safe choice. NGK is highly respected for its reliability and performance in these engines, making it a top-tier alternative. |
| Quality Aftermarket | Autolite, Champion, Denso, Bosch | These are all trusted brands that make reliable spark plugs. Autolite and Champion were common choices for American vehicles of this era and are excellent direct replacements. Denso and Bosch are also solid performers. |
| Performance | MSD | MSD specializes in performance ignition systems. Their plugs are a good choice if you have other ignition upgrades, but they are overkill for a stock engine. |
| Budget-Friendly | Skyward | This brand falls into the economy category. It will get the job done, but may not have the same lifespan or quality control as the more established brands. |
Check Your Engine
The P3500 came with different engines, most commonly the 5.7L (350) and 7.4L (454) V8s. Always confirm your engine size before buying, as they may require different spark plugs.
Known Issues, Recalls, or TSBs
There are no active recalls or Technical Service Bulletins (TSBs) from the NHTSA related to spark plugs for the 1979-1986 GMC P3500. Issues with spark plugs on these vehicles are almost always due to normal wear and tear over time.
Cost to Replace Spark Plugs
The cost for a full set of 8 spark plugs will vary based on the brand and material you choose.
| Item | Estimated Cost |
|---|---|
| Aftermarket Spark Plugs (Set of 8) | $28 - $135 |
| Shop Labor | $120 - $250 |
| Total Estimated Cost | $148 - $385 |
The Importance of Gapping
The 'gap' is the tiny space between the two electrodes at the tip of the spark plug. For your P3500, this measurement is critical. A common gap size for the 5.7L 350 engine is 0.035 inches. Always check the specification for your engine and use a gap tool to measure and adjust each plug before installation. An incorrect gap can lead to misfires and poor performance.
Frequently Asked Questions
Do I need expensive iridium plugs for my P3500?
No. Your 1979-1986 P3500's engine was designed for standard copper core spark plugs. While iridium plugs last longer, they won't provide a noticeable performance benefit on a stock engine of this vintage and are not worth the extra cost.
How often should I change the spark plugs?
For standard copper plugs in these engines, a good interval is every 20,000 to 30,000 miles. Since this is a work vehicle, more frequent checks are a good idea, especially if you notice any of the failure symptoms.
Is replacing the spark plugs a DIY job?
Yes, it is a DIY-friendly job if you have the right tools. However, access can be tight on a P3500 van. The engine cover (doghouse) inside the cab must be removed, and reaching the rearmost plugs can be difficult. You will need a ratchet, various extensions, a universal joint, and a proper spark plug socket.
Should I replace the spark plug wires at the same time?
It's a very good idea. Spark plug wires carry the high voltage to the plugs, and they degrade over time. If the wires are old, cracked, or oily, they can leak voltage and cause the same symptoms as bad plugs. Replacing them with the plugs ensures your entire ignition system is refreshed.
Technical Specifications
OEM Part Numbers: CR43TS
Engine compatibility: 5.7L (350ci) V8, 7.4L (454ci) V8. Recommended Material: Copper Core. Recommended Gap (5.7L): ~0.035 inches (Always verify for your specific engine and plug).
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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.