A Guide to Spark Plugs for the 2003-2012 Infiniti FX35
Keep your FX35's powerful V6 engine running at its peak with the right set of spark plugs.
- You must buy the correct plugs for your engine: VQ35DE for 2003-2008 models and VQ35HR for 2009-2012 models.
- NGK and Denso are the original equipment manufacturers and are the most recommended brands for reliability and performance.
- During replacement, check for oil in the spark plug wells, which indicates failing valve cover gaskets that also need to be replaced.
- New Iridium and Platinum plugs are pre-gapped; do not try to adjust them.
Understanding Your FX35's Spark Plugs
Choosing the right spark plug for your Infiniti FX35 is more important than you might think. The 2003-2012 model years span two different engines, and each requires a specific type of spark plug. Installing the wrong part can lead to poor performance and even engine trouble.
First Generation vs. Second Generation: A Critical Difference
Before buying, you must know which engine your FX35 has. This is the most common mistake owners make.
- 2003-2008 Infiniti FX35: These models have the VQ35DE engine. They came from the factory with NGK Laser Platinum spark plugs.
- 2009-2012 Infiniti FX35: These models use the updated VQ35HR engine. They came from the factory with Denso Iridium spark plugs.
The two plug types are not interchangeable. Always confirm your vehicle's year before purchasing.
Known Issue: Oil in the Spark Plug Tubes
When changing your spark plugs, it is common to find engine oil on the coil pack boots or down in the spark plug wells. This is not caused by a bad spark plug. It is a sign that the valve cover gaskets and/or the spark plug tube seals have become old and are leaking. If you see oil, you should plan to replace the valve cover gaskets 🎬 See how to replace valve cover gaskets on an FX35. to prevent future misfires and damage to the new plugs and ignition coils.
Choosing the Right Aftermarket Spark Plug
Aftermarket spark plugs can be as good as, or even identical to, the ones Infiniti sells, often at a better price. The original parts are made by NGK and Denso, which are available as aftermarket brands.
Brand Quality Tiers
- Tier 1: OEM Equivalent (NGK & Denso): These are the safest choices for your FX35. They made the original plugs for Infiniti. Choosing their Iridium or Laser Platinum series will give you original performance and longevity. Forum members and mechanics strongly recommend sticking with these two brands.
- Tier 2: High-Quality Aftermarket (Bosch): Bosch offers high-quality Double Iridium and Double Platinum plugs that are designed for long life. They are a reliable alternative if you are looking for a reputable brand beyond the original suppliers.
- Tier 3: Economy (Autolite & Champion): These brands provide a budget-friendly option. However, they often use simpler materials like copper or nickel, which may not last as long as the Iridium or Platinum plugs your FX35 was designed for. You may sacrifice longevity for a lower initial cost.
Pro Tip: For the best results, use Iridium plugs. They provide a stronger, more consistent spark and last much longer than platinum or copper plugs, which is what modern engines like the VQ35 are designed for.
Cost of Replacing Infiniti FX35 Spark Plugs
| Category | Estimated Cost (Set of 6) |
|---|---|
| New OEM (from dealer) | $120 - $180 |
| New Aftermarket (Tier 1) | $70 - $150 |
| New Aftermarket (Economy) | $25 - $60 |
| Shop Labor | $175 - $400 |
Cost estimates are approximate and can vary by location and supplier.
Frequently Asked Questions
When should I replace the spark plugs on my FX35?
Infiniti recommends replacing the original iridium-tipped spark plugs around every 100,000 miles. However, if you experience symptoms like a rough idle, poor acceleration, or a flashing check engine light, 🎬 Watch: 7 symptoms of bad spark plugs you shouldn't ignore. your plugs may need to be changed sooner.
Is it hard to change the spark plugs myself?
It is a manageable DIY job for someone with some mechanical experience. The main challenge is access. On the driver's side, the air intake tube must be removed. On the passenger side, wiring harnesses need to be unbolted and moved to reach the ignition coils. The rearmost plugs near the firewall are the most difficult to reach. Expect the job to take 1.5 to 2.5 hours.
Do I need to gap the new spark plugs?
No. Most modern Iridium and Platinum spark plugs come pre-gapped from the factory. Attempting to gap them yourself can easily damage the fine, brittle electrode tip. It is best to install them directly out of the box.
What happens if I don't change my spark plugs?
Old, worn-out spark plugs will cause your engine to run poorly. You will likely experience a rough idle, hesitation when you accelerate, and worse gas mileage. If a plug is failing completely, the unburned fuel from that cylinder can damage your expensive catalytic converter over time.
My car runs rough after changing the plugs. What's wrong?
Some owners report a rough idle immediately after a spark plug change. This can happen because the engine's computer (ECU) had adjusted itself to the old, worn plugs. After installing new plugs, the ECU may need to be reset. You can do this by disconnecting the negative battery terminal for about 15 minutes.
Helpful Videos
Technical Specifications
OEM Part Numbers: 22401-5M015 22401-5M016 22401-JK01D 22401-EW61C
Engine VQ35DE (2003-2008): NGK Laser Platinum PLFR5A-11. Engine VQ35HR (2009-2012): Denso Iridium FXE22HR11 or NGK Laser Iridium DILKAR7B11.
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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.
- Infiniti FX35:
- 🎬 Helpful Videos
- 🛍️ Shop This Part
- Understanding Your FX35's Spark Plugs
- First Generation vs. Second Generation: A Critical Difference
- Known Issue: Oil in the Spark Plug Tubes
- Choosing the Right Aftermarket Spark Plug
- Brand Quality Tiers
- Cost of Replacing Infiniti FX35 Spark Plugs
- Frequently Asked Questions
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