A Guide to Spark Plugs for the 2009-2019 Ford Flex
Keep your Ford Flex's engine running smoothly by understanding when and why to replace your spark plugs.
- For the 3.5L EcoBoost engine, use only OEM Motorcraft or premium Iridium plugs from NGK or Denso to prevent performance issues.
- The official replacement interval is 100,000 miles, but changing plugs earlier (60k-80k miles) is good preventative maintenance.
- Always check the spark plug gap before installation, as it is critical for performance, especially on the EcoBoost engine.
- Replacing the rear three plugs requires removing the upper intake manifold on the non-turbo engine, adding time and complexity to the job.
Signs of Failing Spark Plugs
When spark plugs wear out, they can't create a strong enough spark to ignite the fuel mixture properly. This can cause a variety of noticeable problems. If you experience any of these symptoms, your spark plugs might be the culprit.
- Rough Idling: Your engine may shake or vibrate more than usual when the vehicle is stopped.
- Poor Acceleration: The vehicle may feel sluggish or slow to respond when you press the gas pedal.
- Engine Misfires: You might feel a jerking or stumbling sensation during acceleration as a cylinder fails to fire correctly. This can also trigger a flashing Check Engine Light. 🎬 Watch this video to see a misfire diagnosis in action.
- Reduced Fuel Economy: Worn plugs can cause fuel to be wasted, leading to more frequent trips to the gas station.
- Difficulty Starting: A weak spark can make it harder for the engine to turn over, especially in cold weather.
Choosing the Right Aftermarket Spark Plugs
Your Ford Flex came from the factory with high-quality iridium or platinum-tipped spark plugs, usually made by Motorcraft. When choosing replacements, it's important to match the material and heat range specified for your engine. This is especially critical for the 3.5L EcoBoost engine, which puts more stress on spark plugs due to its turbochargers.
A Note on EcoBoost Engines
The 3.5L EcoBoost engine is sensitive to spark plug quality and gap. Many owners and mechanics strongly recommend using the OEM Motorcraft plugs (part numbers have been updated over the years, from SP-534 to SP-580 and SP-580X) or a top-tier iridium equivalent from NGK or Denso. Using cheaper plugs can lead to misfires and poor performance. Always verify the correct part number for your specific model year.
Aftermarket Brand Tiers
Not all aftermarket brands are created equal. Here’s a general breakdown of the brands available for your Flex:
- Top Tier (OEM-equivalent or better): NGK, Denso, and Motorcraft (which is the OEM brand). These brands are widely trusted for both the Duratec and EcoBoost engines. They use high-quality materials like iridium and platinum that provide long life and consistent performance.
- Mid-Grade (Reliable Alternatives): Bosch and Champion offer good quality plugs that can be a cost-effective choice, especially for the non-turbo 3.5L Duratec engine. Autolite's Iridium XP line is also a solid performer.
- Performance-Focused: Brands like MSD and Accel are geared more towards modified vehicles. While they can offer performance benefits, for a stock Ford Flex, sticking with an OEM-style plug is often the most reliable choice.
Check the Gap!
Even though many modern iridium and platinum plugs come pre-gapped, it's crucial to check the gap with a proper gauge before installation. Shipping and handling can sometimes alter the gap. An incorrect gap can cause misfires and poor performance.
• 3.5L Duratec (Non-Turbo): ~0.049 - 0.053 inches
• 3.5L EcoBoost (Turbo): ~0.030 - 0.033 inches 🎬 See how to properly gap and install EcoBoost spark plugs.
Known Issues, Recalls, and TSBs
No specific recalls or Technical Service Bulletins (TSBs) from Ford or the NHTSA directly target spark plugs for the 2009-2019 Ford Flex. However, failing spark plugs are a very common cause of engine misfire codes (P0300-P0306). The primary "issue" Flex owners face is the replacement process itself, particularly for the rear three cylinders on the V6 engine, which requires removing the upper intake manifold on the Duratec engine.
🎬 Watch this walkthrough for removing the intake to reach rear plugs.| Part Type | Estimated Cost |
|---|---|
| New OEM (Motorcraft) | $45 - $120 |
| New Aftermarket | $35 - $150+ |
| Shop Labor | $200 - $450 |
Frequently Asked Questions (FAQ)
How often should I change the spark plugs on my Ford Flex?
Ford generally recommends replacing the spark plugs every 100,000 miles for both the Duratec and EcoBoost engines. However, many owners, especially those with the EcoBoost engine, choose to replace them sooner (around 60,000-80,000 miles) as preventative maintenance to maintain peak performance and fuel economy.
Is it difficult to change the spark plugs myself?
For the 3.5L V6 engine, the front three spark plugs are easily accessible. However, reaching the rear three plugs requires removing the upper intake manifold on the Duratec engine, which makes the job more complex. The EcoBoost engine provides slightly better access to the rear plugs without removing the manifold. If you are not comfortable with this procedure, it is best to have a professional mechanic do the job.
Do I need to use anti-seize on the new spark plug threads?
Most modern spark plugs, including the Motorcraft OEM plugs, have a special nickel plating on the threads that prevents them from seizing in the cylinder head. For this reason, manufacturers like NGK and Ford often advise against using anti-seize, as it can act as a lubricant and cause you to over-torque the plugs, potentially damaging the cylinder head. Always follow the specific instructions from the spark plug manufacturer.
Should I replace the ignition coils at the same time?
It is not strictly necessary to replace the ignition coils (also called coil-on-plugs) with the spark plugs. However, if your Flex has high mileage or you are already experiencing a misfire, it can be cost-effective to replace the coils at the same time, especially since you will have already done much of the labor to access them. At a minimum, you should inspect the coil boots for any cracks or damage and apply dielectric grease to the inside of the boot before reinstalling.
Helpful Videos
Technical Specifications
OEM Part Numbers: CYFS-12F-5 SP-520 SP-534 SP-580 SP-580X CYFS12YT4X
Engine: 3.5L Duratec V6, 3.5L EcoBoost V6. Plug Material: Iridium or Platinum. Hex Size: 5/8" (16mm). Gap (Duratec): ~0.051 in. Gap (EcoBoost): ~0.031 in.
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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.
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