Subaru Forester Spark Plug Replacement Guide (2020-2024)
Everything you need to know about replacing the spark plugs in your 2020-2024 Forester's boxer engine.
- Replace your spark plugs every 60,000 miles or 6 years as recommended by Subaru.
- The boxer engine makes this a difficult job; expect 2-3 hours of labor and higher shop costs.
- Use high-quality NGK Laser Iridium plugs, as NGK is the original equipment manufacturer.
- Check for oil in the spark plug tubes, which could indicate a leaking gasket (TSB SB22-168).
Understanding Spark Plug Replacement in Your Forester
The spark plugs in your 2020-2024 Subaru Forester are a key maintenance item. Subaru recommends replacing them every 60,000 miles or 6 years, whichever comes first. Pushing them beyond this interval can lead to a noticeable drop in performance and fuel efficiency, and potentially cause more expensive problems. Worn plugs can cause engine misfires, which may trigger a flashing check engine light and can damage your catalytic converter over time.
Symptoms of Failing Spark Plugs
🎬 Watch: A visual guide to common bad spark plug symptoms.
- Rough Idle: Your engine may shake or vibrate more than usual when stopped.
- Poor Acceleration: The car may feel sluggish or hesitant when you press the gas pedal.
- Reduced Fuel Economy: You may notice you're filling up the gas tank more often. Worn plugs can reduce fuel efficiency by up to 30%.
- Engine Misfires: The engine may stumble, and you might see a flashing check engine light. This is often accompanied by fault codes like P0300, P0301, P0302, P0303, or P0304.
- Difficulty Starting: The engine may take longer to crank over before it starts.
OEM vs. Aftermarket Spark Plugs
When it's time for a replacement, you have a choice between Original Equipment Manufacturer (OEM) and aftermarket plugs. For the 2020-2024 Forester, the original factory spark plugs are made by NGK. This means you can buy the same quality part from NGK in an aftermarket box, often for less money than the Subaru-branded equivalent. The recommended part is an NGK Laser Iridium plug, which is designed for long life and high performance. While cheaper copper or basic platinum plugs are available, they are not recommended for this engine and will not last as long. Sticking with a high-quality Iridium plug from a reputable brand like NGK ensures compatibility and performance.
Counterfeit Parts Warning
Be cautious when purchasing spark plugs from online marketplaces like Amazon or eBay. There have been widespread issues with counterfeit NGK plugs that can cause poor performance and even engine damage. It is safest to buy from a reputable auto parts retailer.
Known Issues for 2020-2024 Foresters
- Voluntary Recall WRE-20: Some 2020 models were built with incorrect ignition coils. This could cause a misfire and damage the spark plug. A dealer can check if your vehicle is affected and, if a misfire code is present, may replace the spark plug(s) and ignition coil(s) for free.
- TSB SB22-168: A Technical Service Bulletin was issued for potential oil seepage from the spark plug tube gasket on models up to 2023. This oil can leak onto the spark plug and ignition coil, causing misfires. If you are replacing your plugs, it is a good idea to inspect these seals for any signs of leakage. 🎬 Watch: How to replace leaking spark plug tube seals.
Installation & Replacement Cost
Replacing the spark plugs on a Subaru boxer engine is more difficult than on a typical inline or V-engine. The plugs are on the sides of the engine block, with very little clearance. To access them, the battery and air intake box must be removed. This job is possible for an experienced DIY mechanic but can be frustrating for a beginner.
🎬 See this trick for extracting the difficult driver's side plug.Special Tools Required
You will need a special 14mm thin-wall spark plug socket, a wobble extension, and a variety of different length extensions to complete this job. A standard spark plug socket will not fit.
| Part Type | Cost (per set of 4) |
|---|---|
| New OEM (Dealer) | $140 - $180 |
| New Aftermarket (NGK Iridium) | $75 - $125 |
| Shop Labor | $250 - $450 |
| Total Professional Job | $470 - $600+ |
Frequently Asked Questions
Can I use cheaper spark plugs in my Forester?
It is strongly recommended to use the specified NGK Laser Iridium spark plugs. Cheaper plugs are not designed for the high-energy ignition system in your Forester, will not perform as well, and will wear out much faster, requiring you to repeat the difficult installation process sooner.
Why is the replacement cost so high at a shop?
The majority of the cost is labor. Due to the boxer engine's design, mechanics need to remove other components to access the spark plugs, which takes 2-3 hours. This makes the job significantly more time-consuming than on other vehicles.
What is the spark plug gap for the 2020-2024 Forester?
The NGK Laser Iridium plugs come pre-gapped to the correct specification (0.032 inches or 0.8mm). You should not need to adjust the gap on these plugs, and attempting to do so can damage the fine iridium tip.
Should I replace the ignition coils with the spark plugs?
It is not required, but it is a good preventative measure, especially if your vehicle has over 100,000 miles. An ignition coil failure can cause the same symptoms as a bad spark plug. Since you already have everything taken apart to access the plugs, replacing the coils at the same time can save you from doing the same labor-intensive job twice.
Helpful Videos
Technical Specifications
OEM Part Numbers: 22401AA95A
NGK Part #: DILKAR7Q8 or 91899 Type: Laser Iridium High Ignitability Hex Size: 14mm (Thin Wall Socket Required) Pre-Gapped: Yes (0.032 in / 0.8mm)
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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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