When should I replace my spark plugs on my Subaru Outback?

For most Outback models built in the last decade, you should plan to replace spark plugs around 100,000 miles under normal driving. The exact timing depends on your engine type, the plug material, and how you drive.

Understanding the interval by engine and plug material

Subaru uses different spark plug designs across generations. Many modern Outbacks run iridium or platinum plugs designed for long life, typically around 100,000 miles under normal driving. Older or budget models may have copper-core plugs with shorter lifespans. Always check your owner's manual or ask a Subaru service advisor for your specific model year and engine.

Note: The following guidelines assume normal driving. If you tow, frequently drive in dusty or extreme conditions, or do a lot of short trips, you may want to adjust the replacement interval earlier.

Before listing intervals, here is the general breakdown:

• Most modern Subaru Outbacks (model years roughly 2010 and newer) use iridium or platinum plugs and are designed for replacement around 100,000 miles under normal driving conditions.


• Older Outbacks and certain market variants with copper-core plugs typically have a shorter recommended interval, commonly around 60,000 miles.


• In severe service (short trips, heavy towing, dusty roads, extreme temperatures), consider inspecting or replacing plugs earlier, often around 60,000–90,000 miles regardless of the nominal interval.

Conclusion: For typical owners, 100,000 miles is the baseline, but verify in your manual and adjust for your driving style and environment.

Signs your spark plugs may need replacement sooner

Watch for symptoms that indicate current plugs are worn or fouled. If you notice any of the following, consider replacing them sooner than the listed interval:

• Rough idle or engine misfires, especially at startup or during low-speed acceleration.


• Degraded acceleration, sluggish throttle response, or reduced engine power.


• Poor fuel economy or a noticeable drop in performance; check engine light may illuminate.


• Difficulty starting the engine or frequent stalling.


• Unusual noises from the engine bay, such as ticking or tapping around the spark plug area, or damaged coil boots.

If you notice any of these symptoms, have the ignition system inspected promptly to prevent further engine damage and maintain efficiency.

Replacement process: what to expect

Replacing spark plugs is a common maintenance task, but the exact steps depend on your Outback’s engine. Here is a high-level overview to help you prepare:

1. Confirm the correct spark plugs for your engine and the proper gap. Many newer Subaru plugs are pre-gapped, but always verify the part number in your manual or parts catalog.


2. Disconnect the negative battery terminal to prevent shorts or accidental cranking.


3. Access the spark plugs by removing necessary engine covers and the coil-on-plug packs. In most Subaru engines, each plug sits under a coil; remove the coil’s retaining bolt or electrical connector and lift the coil out carefully.


4. Inspect the coil boots for cracks or damage and replace any damaged boots to prevent misfires.


5. Install the new spark plugs by threading them by hand to avoid cross-threading, then torque to the factory specification using a torque wrench. Do not overtighten.


6. Reinstall the coil packs, reconnect electrical connections, and reconnect the battery. Start the engine and check for smooth operation and absence of misfires.

Replacing spark plugs is typically straightforward for many Subaru Outbacks, but torque specs and coil access can vary by engine. Follow the exact instructions in your manual or consult a professional if you’re unsure.

DIY vs professional service

Even though spark plug replacement is a common DIY task, Subaru’s modern coil-on-plug designs require careful handling and correct torque. If you lack the right tools or are unsure about the sequence, a professional service can perform the replacement quickly and inspect related components such as ignition coils, boots, and seals.

When to seek professional help

Consider a mechanic if you notice misfires after replacement, damaged coil boots, difficulty accessing plugs, or if your engine bay layout makes the job impractical. A shop can also check for other wear or fouling that could affect performance.

Summary

In most Subaru Outback models, the baseline spark plug replacement interval is about 100,000 miles under normal driving. Always confirm the exact interval in your owner’s manual, and adjust for driving style, climate, and conditions. Stay alert for symptoms that suggest wear or fouling, and decide whether to tackle the job yourself or enlist a professional for reliable, long-term performance.

How do I know if my Subaru spark plugs are bad?

One of the first signs of spark plug wear is trouble starting your Subaru. If the engine cranks longer than usual before starting or if you experience intermittent starting issues, it's time to inspect your spark plugs.

Do I really need to change my spark plugs at 100,000 miles?

Yes, replacing spark plugs at 100,000 miles is a common and often necessary maintenance task, as many modern vehicles have spark plugs rated to last that long. However, the exact interval depends on your vehicle's make, model, and the type of spark plug installed, so you should always check your owner's manual for the manufacturer's specific recommendation. 
This video explains when to change spark plugs and what happens if you don't: 1mHonest Mechanic ColoradoYouTube · Dec 24, 2023
Why it's important

• Engine performance: Spark plugs that are past their prime can cause rough idling, poor acceleration, and decreased fuel efficiency. 
• Preventing damage: Over time, worn-out plugs can put extra stress on other components, like ignition coils, and may seize in the engine block, making them harder to remove later. 
• Preventative maintenance: Replacing spark plugs is a form of preventative maintenance that can prevent more costly repairs down the line. 

This video explains why it's important to change spark plugs at 100k miles: 52sWhite One Auto, LLCYouTube · May 19, 2021
What to consider

• Owner's manual: Your vehicle's owner's manual is the most reliable source for the correct replacement interval and recommended plug type. 
• Spark plug type: The lifespan of spark plugs varies by material. Iridium plugs are often rated for 100,000 miles or more, while other types like copper or platinum have shorter lifespans. 
• Driving conditions: Severe driving conditions can shorten the life of spark plugs, so your interval may be shorter than recommended if you frequently tow, drive in extreme temperatures, or frequently start and stop. 

How much does it cost to replace spark plugs on a Subaru Outback?

The cost to replace Subaru Outback spark plugs typically ranges from approximately $300 to over $800, with prices varying by model, location, and whether you choose a dealership or an independent mechanic. Dealerships generally have higher labor rates and use OEM parts, leading to a higher price, while independent shops may be less expensive. Newer models with more complex engine layouts can sometimes have higher costs, and labor is often the most significant part of the total price.
 
Factors that influence the cost
This video explains what to consider when buying spark plugs: 30sMrSubaru1387YouTube · Jan 9, 2022

• Location and mechanic: Dealerships and independent shops have different pricing structures. Dealerships typically charge more for labor and use official parts, while independent shops can be more affordable. 
• Engine and model year: The specific model and year can impact the cost. Some engine configurations are more labor-intensive, driving up the final price. 
• Parts: The cost of the spark plugs themselves can vary. Genuine Subaru parts are often more expensive than aftermarket options. 
• Labor: Since replacing spark plugs can be a time-consuming job, the labor cost is often the largest portion of the total bill. 

Examples of recent costs (from customer reports)

• $409: Paid at a dealership for a 2020 Outback. 
• $500+: Paid at a dealership for a 2019 Outback. 
• $300: Paid at an independent shop for a 2019 Outback. 
• $225: Paid at a private mechanic for a 2017 Outback. 
• $275: Quoted for a 2018 Outback at an independent shop. 

How often do spark plugs need to be replaced on a Subaru Outback?

The spark plug replacement interval for a Subaru Outback is typically every 60,000 miles, but you should always consult your owner's manual for the specific mileage recommended for your model and engine type. Some models with turbocharged engines may have a slightly different interval, and long-life spark plugs like platinum or iridium can last longer than conventional plugs. 
Key recommendations

• Check your owner's manual: This is the most accurate source for your specific vehicle's recommended maintenance schedule. 
• 60,000 miles is a common interval: This is the standard replacement interval listed in many maintenance schedules for the Outback. 
• Consider your engine type: Models with turbocharged engines may have a slightly different interval than non-turbocharged models. 
• Long-life plugs: If your Outback has platinum or iridium-tipped plugs, they can last significantly longer, potentially 100,000 miles or more. 
• Preventative maintenance: Replacing spark plugs at the recommended interval can prevent future engine issues like misfires and ensure consistent ignition.