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If your Forester from 1998 to 2002 is showing rough idle, hard cold starts, or reduced fuel economy, worn or incorrect spark plugs are a common and fixable cause. Picking the right spark plugs matters for ignition consistency, drivability, and long-term engine health on these Subaru engines. This guide shortlists the top plug options compatible with the 1998-2002 Forester and explains the performance and durability tradeoffs so you can match a choice to your driving style and maintenance plan. We evaluate candidates for ignition performance, longevity, heat range, and ease of installation so you know what to expect before you open the hood.
Looking for other parts? See all Subaru Forester parts & accessories.
Top Picks at a Glance
| Best Overall The best all-around choice for most situations | NGK G-Power BKR6EGP Platinum Spark Plug (8-Pack) |  |
| Best Quality Built to a higher standard if you want something more solid | NGK Laser Iridium Spark Plugs, 4-Pack for Subaru Forester 2.5L H4 (1998–2010) |  |
| Best Value The sweet spot between price and what you get | Genuine Subaru Spark Plugs 22401AA310 — Set of 4 |  |
| Best Budget The cheapest option that still gets the job done reliably | NGK BKR5E-11 Spark Plug (pack of 4) |  |
| Highest Rated A top-rated pick with lots of positive feedback | NGK BKR5EGP G-Power Nickel Spark Plug, Pack of 4 |  |
| Most Popular A crowd favorite that many people choose with confidence | NGK BKR5E-11 Copper Spark Plug — Set of 4 |  |
| Best Seller A high-volume bestseller chosen again and again | NGK G-Power Platinum Spark Plug BKR5EGP — 6 Pack |  |
1. NGK G-Power BKR6EGP Platinum Spark Plug (8-Pack)
| Brand | NGK |
|---|---|
| Core Material | Platinum |
| Thread Size | 14mm |
| Manufacturer Part Number | BKR6EGP |
These NGK G-Power BKR6EGP plugs are factory-quality platinum replacements sold in an eight-pack for doing a full tune-up. They use a platinum-tipped design for longer life and consistent spark delivery compared with standard copper plugs, which helps maintain smooth idle and steady throttle response during everyday driving. Installation is the same as any threaded 14mm plug and they fit front or rear positions where this heat range and thread spec are required. Practical strengths are durability and predictable performance between services, making them a convenient choice if you prefer fewer spark plug changes and a straightforward swap during routine maintenance. They are not a performance upgrade for forced-induction or high-boost tuning, and drivers seeking maximum ignition performance or long-reach specialty plugs should consider other options. For regular street-driven cars the plugs balance longevity and reliable ignition without extra complexity.
Best for: Practical owners who want a reliable, longer-lasting factory-replacement spark plug for routine maintenance on a daily-driven vehicle and value fewer service intervals.
Less Ideal for: Drivers building high-performance, high-boost, or race engines who need specialty or iridium/tuned plugs should look elsewhere.
- Platinum center electrode for extended service life compared with standard copper plugs
- Sold in an eight-pack for full-engine tune-ups without buying multiple single units
- Matches common 14mm thread size and factory replacement fitment for easy installation
- Consistent spark delivery supports smooth idle and steady throttle response in everyday driving
- Not intended as a high-performance or racing plug for turbocharged or heavily modified engines
Verdict: Choose these NGK platinum G-Power plugs if you want a dependable, longer-lasting factory-style replacement to simplify tune-ups on a street-driven Subaru Forester.
2. NGK Laser Iridium Spark Plugs, 4-Pack for Subaru Forester 2.5L H4 (1998–2010)
| Brand | NGK |
|---|---|
| Manufacturer Part Number | 4024161339 |
| Compatible Engine | 2.5L H4 Subaru Forester |
| Pack Quantity | 4 |
These NGK Laser Iridium spark plugs replace the factory plugs in the 2.5L Subaru Forester and are built around a fine-wire iridium center electrode and a plated ground electrode for improved ignitability. In normal use they deliver stronger, more consistent sparks than standard copper plugs which helps smoother starts, steadier idle, and more complete combustion under load. The construction includes a copper core for heat transfer and application-specific electrode geometry to match Subaru ignition requirements. That combination supports extended service life and predictable performance up to the typical iridium interval, so you can go longer between changes. Practical limitations are that iridium plugs cost more than basic replacements and you should confirm exact fitment before installation; they also will not fix mechanical or fuel-system issues. For owners chasing crisper throttle response and reliable ignition in a stock or mildly tuned Forester, these offer a straightforward, durable upgrade.
Best for: Drivers who prioritize sharper throttle response and reliable ignition in a 1998–2002 Subaru Forester and want a longer-lasting, performance-focused replacement.
Less Ideal for: If you are on a strict budget or plan frequent engine tuning changes that require different plug heats or gaps, a lower-cost standard plug or specialist racing plug may be a better fit.
- Fine-wire iridium center electrode for improved ignitability and fuel burn
- Application-specific electrode geometry for consistent firing in Subaru 2.5L engines
- Copper core promotes efficient heat transfer to help prevent fouling and hot spots
- Longer service life compared with standard copper plugs
- Higher up-front cost compared with basic replacement plugs
Verdict: Choose these NGK Laser Iridium plugs if you want a durable, performance-minded ignition upgrade that delivers crisper throttle response and longer service life for your 1998–2002 Forester.
3. Genuine Subaru Spark Plugs 22401AA310 — Set of 4
| Manufacturer Part Number | 22401AA310 |
|---|---|
| Unit Count | 4.0 Count |
| Thread Size | 14mm |
| Core Material | Copper |
These Genuine Subaru spark plugs are a direct-fit replacement sold in a set of four and intended for non-turbo Subaru four-cylinder engines. They use copper cores and factory-specified thread size for straightforward installation with standard tools. In typical use you swap all four plugs during a routine tune-up to restore consistent firing, smoother idle, and reliable cold starts on supported Forester models. The key practical benefits are exact fitment to Subaru specifications and OEM-grade materials, which reduce the risk of fitment issues, misgapping, or premature failure that can occur with some aftermarket units. Because they are copper-core plugs, they provide good conductivity and perform well for everyday driving, but they do not offer the longer service life or higher heat-range tolerance of platinum or iridium options, so expect more frequent replacements under heavy use. Overall they are a sensible, no-nonsense choice if you prioritize factory-fit reliability and predictable serviceability for routine maintenance.
Best for: Buyers who want a straightforward, factory-spec replacement that restores original ignition performance with minimal fuss and compatibility concerns for routine maintenance.
Less Ideal for: Drivers seeking maximum longevity or high-performance ignition parts should consider platinum or iridium plugs instead.
- Factory replacement fitment reduces installation guesswork and fitment issues
- Copper core offers strong electrical conductivity for reliable ignition under normal driving
- Sold as a set of four so you can replace all cylinders at once for consistent performance
- Copper construction has shorter service life than platinum or iridium alternatives
Verdict: Choose these genuine Subaru spark plugs when you want a direct, factory-quality replacement to restore reliable ignition during standard maintenance.
4. NGK BKR5E-11 Spark Plug (pack of 4)
| Thread Size | 14 millimeters |
|---|---|
| Gap Size | 0.9 millimeters |
| Compatible with Vehicle Type | Car, Truck |
| Core Material | Copper |
These NGK BKR5E-11 plugs are straightforward, factory-quality replacement spark plugs intended for vehicle-specific applications. With a copper core and nickel-plated metal top, they deliver the familiar ignition characteristics you expect from a standard replacement part and are commonly used where factory copper plugs are specified. Installation is typical for spark plugs: remove the old plugs, check torque and gap, and fit the BKR5E-11 to the recommended 0.9 mm gap. The resistor design helps reduce radio interference and the 14 mm thread size matches many passenger car and truck cylinder heads. As a budget-friendly option, they give dependable starting, idle smoothness, and predictable fuel burn without the cost of platinum or iridium types. The limitation is that copper plugs wear faster than precious-metal alternatives, so they will need replacement more often under high-mileage or high-heat conditions. For routine maintenance on a compatible 1998–2002 Subaru Forester engine that calls for a copper plug, these are a sensible, economical choice.
Best for: Buyers seeking an economical, factory-equivalent replacement for routine maintenance on a compatible Forester who prioritize reliable starting and normal driving rather than extended service intervals.
Less Ideal for: Drivers chasing maximum longevity, higher-mileage intervals, or marginal performance gains should consider precious-metal spark plugs instead.
- Factory-style copper core for predictable ignition performance
- Resistor design reduces radio and ignition interference
- Vehicle-specific fit and common 14 mm thread size simplify installation
- Affordable, cost-effective option for routine maintenance
- Copper construction has shorter service life than platinum or iridium plugs
Verdict: A sensible, budget-friendly factory-style replacement for routine spark plug maintenance on compatible 1998–2002 Subaru Forester engines.
5. NGK BKR5EGP G-Power Nickel Spark Plug, Pack of 4
| Brand | NGK |
|---|---|
| Core Material | Platinum |
| Thread Size | 14 millimeters |
| Vehicle Service Type | Car, Truck |
| OEM Part Number | BKR5EGP |
These NGK G-Power nickel spark plugs are a straightforward, reliability-focused replacement for compatible Subaru Forester engines. They use a v-groove center electrode and a high-purity copper core to improve ignitability and heat dissipation, which helps consistent starting and reduces the chance of overheating in everyday driving. Trivalent plating and cold-rolled threads reduce the risk of cross-threading and eliminate the need for anti-seize, making installation simpler and less risky for DIYers and techs alike. The 0.6 mm platinum tip on some NGK variants maintains a stable gap over time for longer service intervals compared with plain nickel plugs. Expect steady performance for daily commuting and light towing without the sensitivity or higher voltage demands of ultra-fine iridium plugs. Note that these are a conventional nickel/platinum design rather than a premium iridium or ruthenium option, so peak performance and maximum longevity will be less than top-tier specialty plugs.
Best for: Drivers who prioritize dependable, easy-to-install replacement plugs that restore consistent starting and mid-range drivability for everyday use in a 1998–2002 Forester.
Less Ideal for: Drivers seeking maximum longevity or the smallest performance gains for high-output or heavily modified engines should consider iridium or ruthenium plugs instead.
- Improved ignitability from v-groove center electrode for reliable starts
- Copper core improves heat dissipation to reduce overheating risk
- Trivalent plating and cold-rolled threads reduce installation damage and remove need for anti-seize
- Pack of four covers a full engine tune-up for a typical 4-cylinder Forester
- Not a premium iridium or ruthenium tip so longevity and peak performance are lower than specialty high-end plugs
Verdict: A practical, reliability-first spark plug set that delivers consistent starts and straightforward installation for routine Forester maintenance.
6. NGK BKR5E-11 Copper Spark Plug — Set of 4
| Thread Size | 14mm |
|---|---|
| Compatible with Vehicle Type | Car |
| Automotive Fit Type | Vehicle Specific Fit |
| Core Material | Copper |
These NGK BKR5E-11 plugs are a straightforward factory-quality replacement arranged as a set of four. They use a copper core with a metal top and a 14mm thread, which makes them suitable where the 1998–2002 Subaru Forester specifies a copper-type spark plug and a 14mm thread size. In everyday use they restore consistent ignition timing and smooth idle after worn plugs are replaced, and their OEM-grade construction favors predictable longevity and compatibility. Installation is typical for standard spark plugs and they work well with stock ignition systems; no special gapping or heat-range modification is usually required if they match the Forester application. The main limitation is that copper plugs wear faster than iridium or platinum alternatives, so they may need replacing more often under high-mileage or performance use. For buyers who value reliable, factory-style replacements backed by widespread use, these NGK plugs are a safe, low-risk choice.
Best for: A buyer who wants a low-risk, factory-style replacement that restores stock ignition performance on a 1998–2002 Subaru Forester without upgrading to premium electrode materials.
Less Ideal for: Drivers seeking the longest-lasting or high-performance plugs for modified engines should consider platinum or iridium options instead.
- Factory-quality construction from a major OEM supplier
- Copper core promotes good conductivity and predictable ignition
- 14mm thread and vehicle-specific fit reduce fitment risk
- Sold as a set of four for full-engine replacement
- Copper core wears faster than iridium or platinum alternatives
Verdict: Choose these NGK copper plugs if you want a trustworthy, factory-style four-pack replacement that restores stock ignition behavior on a 1998–2002 Subaru Forester.
7. NGK G-Power Platinum Spark Plug BKR5EGP — 6 Pack
| Core Material | Copper |
|---|---|
| Top Material Type | Ceramic, Metal |
| Thread Size | 14mm x 1.25mm |
| Position | Center |
These NGK G-Power platinum spark plugs are a direct-fit replacement sold in a pack of six for routine spark plug service. They use a platinum-tipped ground electrode and a copper core with a high-strength alumina silicate ceramic insulator to deliver consistent spark performance and good heat transfer. The trapezoid-cut ground electrode and corrugated ribs help reduce quenching and prevent flashover, which can improve ignition stability and cold-start response compared with worn plugs. Trivalent metal plating on the threads reduces corrosion and seizing, which makes installation and future removal easier for maintenance-minded owners. They are best used as factory-style service parts for vehicles that specify this resistor-type plug and the 14mm x 1.25mm thread size. Limitations are that these are not an iridium or multi-electrode performance plug, so you should not expect extended interval life beyond typical platinum longevity or gains for high-performance tuning applications.
Best for: A risk-averse Forester owner who wants a dependable, factory-style replacement to restore reliable ignition and easy maintenance without changing the engine tune.
Less Ideal for: Drivers seeking maximum longevity or small performance gains from high-end iridium plugs or those doing performance modifications should consider higher-end alternatives.
- Platinum-tipped electrode offers improved wear resistance over standard copper plugs
- Corrugated ribs and trapezoid ground reduce flashover and quenching for steadier ignition
- Trivalent plating on threads resists corrosion and makes removal easier
- Sold in a 6-pack so you can replace all cylinders at once
- Not a premium iridium design so lifespan and marginal performance gains are lower than top-tier performance plugs
Verdict: A straightforward, factory-replacement platinum spark plug pack that restores reliable ignition and simplifies maintenance for risk-averse owners.
Choosing the Right 1998-2002 Subaru Forester Spark Plug: Key Factors to Consider
Ignition Consistency
Consistent ignition across idle, throttle transitions, and cold starts directly affects drivability on the 1998-2002 Forester. A plug that maintains a stable spark helps eliminate hesitation, rough idle, and intermittent misfire signs that owners commonly report.
Materials and electrode design influence how reliably a plug fires under varied engine loads. For Forester engines, look for plugs that retain their electrode profile and gap over many miles so your timing and fuel delivery remain effective without repeated tune-ups.
Heat Range
Heat range determines how quickly a plug sheds combustion heat to the cylinder head and operates within the correct temperature window. Using a plug that runs too hot can cause pre-ignition or electrode wear, while a plug that runs too cold can foul from deposits and cause misfires.
For the Forester, choose plugs with a heat range suited to the factory ignition timing and typical driving conditions in your area. If you often tow, drive in hot climates, or have modified timing, adjust the heat range accordingly, but for stock engines stick close to the OEM recommendation for reliable service life.
Electrode Material and Longevity
Electrode composition, such as copper, platinum, or iridium, affects both spark efficiency and how long the plug maintains its gap. Iridium and platinum electrodes typically offer longer service life and more consistent performance over time compared with standard copper cores.
Longer-life electrodes reduce maintenance frequency, which matters if you prefer infrequent tune-ups. However, consider whether the vehicle will benefit from extended-life plugs given driving habits and whether you routinely change plugs at recommended intervals.
Spark Plug Gap and Tolerances
Correct spark plug gap is critical for optimum spark energy and combustion. A gap that is too wide can overtax the ignition coil and cause misfires, while a gap that is too narrow can produce weak ignition and reduced efficiency.
Check the specified gap for the 1998-2002 Forester and verify whether the plug arrives pre-gapped or requires adjustment. Some fine-wire tips are more delicate and should be gapped carefully with the right tools to avoid damaging the electrode.
Fitment and Thread Specifications
Proper thread size, reach, and seating are essential to avoid cross-threading or reaching issues that can damage the head. The correct plug must match the Forester's cylinder head depth and thread pitch to ensure secure installation and proper heat transfer.
Always confirm fitment details for the 1998-2002 Forester so the plug seats correctly and the gasket or washer type matches expectations. Incorrect reach or thread differences can lead to combustion sealing problems or localized overheating.
Serviceability and Installation
Ease of installation and serviceability are practical factors many owners value. Plugs that accept standard socket sizes, are available with clear gap specs, and do not require specialty tools make routine maintenance simpler.
If access to the spark plugs is tight under the intake or ignition leads on your Forester, consider plug designs that make removal and reinstallation less fiddly. Also factor whether the plug's construction tolerates routine torque without risk of breaking or galling.
How Spark Plug Heat Range Affects Forester Performance
The correct heat range keeps the plug tip hot enough to self-clean carbon deposits while avoiding temperatures that invite pre-ignition. On 1998-2002 Forester engines, maintaining that balance supports steady idle, prevents fouling during short trips, and reduces the chance of detonation under load.
When evaluating options, look for clear heat-range data and guidance on whether a plug is a direct-equivalent to factory recommendations. Small shifts in heat range can noticeably change how the engine behaves during city driving versus highway cruising.
- Running too hot increases electrode erosion and risk of pre-ignition.
- Running too cold leads to carbon fouling and misfires on short trips.
- Choose a plug that suits your dominant driving conditions and any engine modifications.
Symptoms That Point To Worn or Incorrect Spark Plugs
Several common symptoms on the Forester suggest plug attention: rough idle, hard cold starts, decreased fuel economy, and sporadic engine misfire codes. Cold-start misfire issues often present as prolonged cranking or stutter right after starting.
Identifying whether a symptom is plug-related vs. other ignition or fuel issues often requires a combination of visual plug inspection and basic diagnostics. Look for excessive electrode wear, heavy carbon deposits, or oil fouling when removing plugs.
- Hard starting or long cranking times.
- Rough idle or intermittent stalling.
- Decreased fuel economy and hesitation on acceleration.
Gap Setting And Basic Installation Tips
Setting and verifying the correct spark plug gap ensures the ignition system operates within expected parameters. Use a feeler gauge or gap tool and set the gap to the specification recommended for the Forester engine. Fine-wire plugs can be fragile, so use care when adjusting.
When installing, apply the correct torque to avoid damaging the cylinder head or plug. Hand-start the plug to avoid cross-threading and tighten to the specified torque range. If a gasket-type seat is used, replace crush washers as needed to ensure a proper seal.
- Always check and set the gap before installation.
- Hand-start threads to avoid cross-threading, then torque to spec.
- Replace crush washers if applicable and inspect ignition boots for wear.
Choosing Between Long-Life And Standard Plugs
Long-life plugs such as those with iridium or platinum tips last significantly longer than basic copper plugs, reducing how often you need to perform plug service. For owners who drive many miles between maintenance intervals, investing in longer-life electrodes can make sense.
However, if you perform regular tune-ups on schedule or prefer lower initial cost and simpler service, standard plugs can still provide reliable performance. Consider driving pattern, maintenance habits, and whether you prefer extended intervals when deciding which type to prioritize.
- Iridium/platinum: longer life, consistent gap retention.
- Copper: lower initial cost, easier to re-gap in some cases.
- Match the choice to your maintenance cadence and driving demands.
Troubleshooting Persistent Misfires
If swapping plugs does not cure misfires, expand diagnostics to ignition coils, wiring, and fuel delivery. Misfires that persist after correctly gapped, properly torqued new plugs often indicate coil pack degradation or fuel injector issues rather than plug failure.
Use systematic checks: inspect plug condition, verify coil output where possible, and monitor for codes that identify specific cylinders. Addressing root causes prevents repeatedly replacing plugs without resolving the underlying issue.
- Check coils and wiring for damage or arcing.
- Confirm fuel pressure and injector function if misfires persist.
- Inspect plugs for oil fouling that could indicate valve cover gasket leaks.
Still looking for the perfect fit?
Select your Subaru Forester configuration to see the most relevant Spark Plugs recommendations
How We Chose the Best 1998-2002 Subaru Forester Spark Plug
We narrowed the selection using criteria that reflect real-world needs for 1998-2002 Subaru Forester owners. First, ignition consistency: plugs had to deliver repeatable spark energy across idle, cruise, and cold-start conditions relevant to these engines. Second, longevity and electrode wear resistance were considered to reduce maintenance frequency while preserving performance. Third, appropriate heat range and heat-shedding characteristics were required to match the Forester's factory timing and typical operating temperatures. Fourth, compatibility and correct thread fitment were verified for the model years in scope to avoid fitment issues. Fifth, installation practicality was assessed, including spark plug gap tolerances and whether standard tools suffice. We excluded any options lacking documented fitment for the 1998-2002 Forester, plugs intended solely for racing or modified engines with extreme timing changes, and parts without clear heat-range information. The final list balances real-world durability, ignition quality, and straightforward serviceability for typical Forester owners.
Our full evaluation process is outlined in our review methodology.
FAQ
How often should I change spark plugs on a 1998-2002 Forester?
It depends on plug type and driving habits. Standard copper plugs often need replacement more frequently, while iridium or platinum plugs can last longer. Follow manufacturer service intervals and inspect plugs if you notice rough idle or starting issues.
Can a bad spark plug cause a cold start misfire on my Forester?
Yes. Worn or fouled plugs commonly cause misfires on cold starts, producing long cranking or hesitation immediately after starting. Visual inspection of removed plugs helps confirm if fouling or electrode wear is present.
Do I need special tools to change the spark plugs on these Forester years?
Most plug changes require a spark plug socket, extension, ratchet, torque wrench, and a gap tool. No specialty tools are typically needed for the 1998-2002 Forester unless access is restricted by aftermarket components.
Should I change the gap on pre-gapped long-life plugs?
You should verify the gap even if plugs come pre-gapped. Fine-wire long-life tips can be fragile, so if adjustment is needed, use the correct tool and minimal force to avoid damaging the electrode.
What does a fouled spark plug look like on my Forester?
A fouled plug may have heavy black carbon deposits, oily residue, or glazed white buildup depending on the cause. Each pattern points to different issues, such as rich running, oil leaks, or overheating, which guides further diagnosis.
Can I use a colder or hotter plug for performance reasons?
Altering heat range should only be done with clear intent. A colder plug can resist pre-ignition in high-load or modified engines, while a hotter plug helps burn deposits in low-use engines. For stock Foresters, stick close to recommended heat ranges unless you have compensating modifications.
Final Verdict
For 1998-2002 Subaru Forester owners, prioritize plugs that match the correct heat range and offer reliable ignition consistency. Decide between long-life electrode materials for reduced service intervals or standard plugs if you prefer lower initial cost and planned maintenance. Verify gap and fitment at installation and use proper torque to protect the cylinder head.Balance your driving habits, maintenance cadence, and any engine changes when selecting spark plugs. Focusing on heat range, electrode material, and correct gap will deliver the most noticeable improvements in starting, idle smoothness, and long-term reliability.
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