Choosing the Right Spark Plugs for Your 1966-1972 Fargo D100 Pickup
Get your classic Fargo running smoothly with the correct spark plugs and avoid common mistakes.
- Stick with standard copper-core spark plugs from brands like Champion or Autolite for best performance.
- Always set the spark plug gap to 0.035 inches before installation using a gapping tool.
- If you have a Slant-6 engine, remember to remove the metal gasket ring from the new spark plugs before installing them.
- A spark plug change is a simple, low-cost maintenance item that can significantly improve your truck's performance and reliability.
Signs of Failing Spark Plugs
Your 1966-1972 Fargo D100 doesn't have a check engine light to tell you when something is wrong. You have to pay attention to how the truck drives and sounds. When spark plugs wear out, they don't create a strong, consistent spark, which leads to several noticeable problems.
- Rough Idle: The engine may shake or vibrate more than usual when the truck is stopped.
- Engine Misfires: You might feel a stumble or hesitation from the engine, especially when accelerating. This feels like a momentary loss of power.
- Poor Acceleration: The truck may feel sluggish or weak when you press the gas pedal.
- Reduced Fuel Economy: If you find yourself visiting the gas station more often, worn plugs could be wasting fuel due to incomplete combustion.
- Hard Starting: A weak spark can make it difficult for the engine to fire up, particularly on cold mornings.
Choosing the Right Aftermarket Spark Plugs
For a classic truck like the Fargo D100, the newest technology isn't always the best. The ignition systems on these trucks were designed for traditional, standard copper-core spark plugs. Fancy iridium or platinum plugs are not necessary and may not perform as well with the original ignition system.
Since the Fargo D100 is mechanically identical to the Dodge D100, parts are interchangeable. The original equipment (OEM) plugs were often from Champion, which is now a readily available aftermarket brand.
Aftermarket Brand Tiers for Fargo D100
| Tier | Brands | Our Price Range (per plug) | Notes |
|---|---|---|---|
| Standard Replacement | Autolite, Champion | $3.50 - $9.31 | This is the recommended choice. Both brands offer reliable, copper-core plugs that work perfectly with the stock ignition system. Champion was the original supplier for many Mopar vehicles of this era. Autolite is also a highly-regarded option trusted by many classic vehicle owners. |
Pro Tip: Check the Gap!
Always check the spark plug gap before installation. The standard gap for nearly all Slant-6 and V8 engines in this era is 0.035 inches. Use a feeler gauge or gapping tool to ensure this measurement is correct. Do not trust the out-of-the-box setting.
Known Issues & Common Mistakes
While there are no formal recalls or TSBs for spark plugs on a vehicle of this age, there are common issues known to owners, especially for the Slant-6 engine.
- Slant-6 Crush Washer: On 1963-1974 Slant-6 engines, the cylinder head is designed for a taper-seat spark plug. Most new plugs come with a removable metal gasket ring (crush washer). This washer should be removed before installing the plug. Leaving it on can cause the plug to sit too high in the head, affecting performance.
- Socket Size: Original plugs often used a 13/16" socket, while many modern replacements use a 5/8" socket. Make sure you have both sizes on hand to remove the old plugs and install the new ones.
- Spark Plug Tubes: The Slant-6 engine uses spark plug tubes that can make access difficult. Take care when removing and reinstalling them to avoid oil leaks. Some owners find a flexible socket extension helpful.
Frequently Asked Questions (FAQ)
How often should I change the spark plugs on my Fargo D100?
For standard copper plugs in these trucks, a good interval is every 20,000 to 30,000 miles. However, since these are often not daily drivers, it's best to inspect them annually for wear, fouling, or corrosion as part of a regular tune-up.
Can I use modern Iridium or Platinum plugs in my classic Fargo?
While they might physically fit, it is not recommended. The original ignition systems have lower energy and were designed specifically for copper-core plugs. Sticking with standard Champion or Autolite copper plugs will provide the most reliable performance.
What is the correct spark plug for my 318 V8 engine?
A common recommendation for the 318 V8 is the Champion RN12YC, which is a standard copper plug. However, always cross-reference part numbers to ensure the best fit for your specific year and engine configuration.
Do I need a torque wrench to install spark plugs?
Using a torque wrench is highly recommended to avoid over-tightening, which can damage the cylinder head, or under-tightening, which can allow the plug to back out. A common torque spec for these engines is around 10-15 ft-lbs, but you should always verify with a service manual. If you don't use one, the general rule is to tighten the plug until it's snug, then give it another quarter-turn.
Technical Specifications
Recommended Plug Type: Standard Copper Core Recommended Gap: 0.035 inches Common Hex Sizes: 13/16" or 5/8" Engine Compatibility: Slant-6 (225ci), V8 (318ci)
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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.