How hard is it to change spark plugs on a Subaru Forester?

Changing spark plugs on a Subaru Forester is a doable DIY task, but the level of difficulty depends on the model year and engine layout. Most owners can complete the job in about 1.5 to 3 hours with common hand tools, though newer FA/FB engines and turbo variants can be tighter and require more time or careful disassembly.

Understanding the difficulty by engine layout

The Forester uses a horizontally opposed (boxer) engine layout. Spark plugs are fitted to each cylinder and are accessed via coil-on-plug assemblies. In many Forester engines, all four plugs can be reached from the top after removing the engine cover and coil packs, but space around the rear plugs can be tight and may require moving or removing other components. Some model years or engine variants carry more routing of hoses and electrical connectors, which increases the challenge.

Access considerations by model/year

Access to spark plugs is highly dependent on the engine family and year. Front plugs are usually accessible from the top, while rear plugs may require navigating tight spaces, and in some cases removing the intake plenum, throttle body, or related components to gain clearance. Turbocharged or performance-oriented variants can add extra steps and complexity.

Before you begin, know that Subaru designs emphasize the coil-on-plug setup, which means you’ll remove the ignition coils one by one rather than traditional spark plug wires. This simplifies some steps but also means you’ll handle multiple delicate connectors and boots during the job.

What you’ll need to do the job

Having the right tools and parts on hand will make the project smoother. Prepare for a mix of basic hand tools and a few specialty items, plus care to avoid common installation mistakes such as cross-threading plugs or over-tightening them.

• Correct spark plugs for your Forester’s engine (check the owner’s manual or a trusted parts source for the exact plug type and heat range; most 4-cylinder models use iridium or platinum plugs and a precise gap).


• Spark plug socket with a rubber insert and a long extension


• Ratchet, small 3-inch and longer extensions as needed


• Torque wrench or foot-pounds torque tool to reach the manufacturer’s spec


• Coil removal tool or small flathead screwdriver to release spring clips on coil packs


• Dielectric grease for coil boots (optional but helpful)


• Anti-seize avoidance note: do not use anti-seize on spark plugs unless the service manual explicitly allows it


• Electrical contact cleaner and rags for cleaning around the plug wells


• Replacement gaskets or sealing components if you remove any intake plumbing or the plenum

Note: If you end up needing to remove the intake plenum, throttle body, or other components to access rear plugs, you’ll want a little extra time, follow a proper reassembly sequence, and reference the service manual for torque specs and reassembly steps.

Step-by-step overview of the replacement process

Here is a high-level guide to give you the general flow. Always refer to the specific service manual for your model year to confirm torque specs and any model-specific steps.

• Disconnect the battery and remove the engine cover if equipped to expose the ignition coils and spark plugs.


• Unclip and remove each ignition coil one at a time, keeping track of which coil belongs to which cylinder.


• Carefully remove the old spark plugs using a magnetic socket, taking care not to disturb surrounding wiring or hoses.


• Check the gap on new plugs (if pre-gapped is not guaranteed) and set to the manufacturer’s specification. Install the new plugs by hand to avoid cross-threading, then tighten to the recommended torque.


• Reinstall each ignition coil on its corresponding plug, reconnect the electrical connector, and ensure the boots seat snugly with a dielectric grease if used.


• Reassemble any components you removed (engine cover, intake parts, etc.), reconnect the battery, and start the engine to confirm smooth operation and check for misfires.

Completing the steps with care will help minimize misfires and ensure a proper seal on the threads. If you’ve replaced coils in the process or encountered stubborn plugs, take extra time to clean the plug wells and check for damaged boots before reassembly.

Model-year considerations and tips

Different Forester generations (EJ, FA/FB, and turbo variants) have distinct access quirks. Budget longer time for rear-plug access on some FA/FB engines and for engines where intake components must be removed to gain clearance. If you’re unsure or your Forester is a turbo or high-mileage example, consider watching a few model-specific video guides or consulting a workshop manual to confirm the exact steps.

Summary

For most Subaru Forester owners, spark plug replacement is a manageable DIY project, but it sits in the moderate difficulty range. Expect 1.5 to 3 hours for a straightforward top-access job on standard 4-cylinder engines, with longer times if you need to remove intake components or if spaces are particularly tight. Use the correct plugs, follow the torque specifications, and handle coil packs and wiring with care. When in doubt, especially on newer FA/FB engines or turbo models, consult the official service manual or a qualified technician to ensure proper procedure and sealing.

What is the most common problem with the Subaru Forester?

The most common problem with the Subaru Forester is the continuously variable transmission (CVT), which can suffer from issues like shuddering, delayed acceleration, and whining noises, and may require expensive repairs. Other frequent issues include problems with the engine (especially oil consumption), the electrical system, and, in certain model years, issues with windshields cracking and batteries dying quickly.
 
You can watch this video to learn more about Subaru Forester common problems: 51scar PROblemsYouTube · Feb 19, 2024
Transmission (CVT)

• Shuddering and jerking: This often occurs when accelerating from a stop.
• Delayed acceleration and slipping: The engine revs up but the car doesn't speed up as expected, which can be dangerous when merging.
• High-pitched whining: This can be a sign of worn pulley bearings inside the transmission.
• Repair cost: CVTs are often not rebuildable and require a complete, expensive replacement. 

Engine

• Excessive oil consumption: Many model years, particularly from the 2014-2018 generation, are known for burning through oil rapidly.
• Oil leaks: Leaks, often requiring expensive engine replacements, are another reported problem. 

Electrical and other issues

• Electrical malfunctions: Issues can range from infotainment system glitches and GPS errors to more serious problems like a battery dying prematurely or the EyeSight safety system turning off unexpectedly. 
• Air conditioning (AC): Some models experience AC failure that can be costly to fix. 
• Windshields: In the 2019-2024 generation, windshields can crack from small chips. 
• Airbag malfunctions: Older models, such as the 2009-2011, have been associated with malfunctioning airbags. 

This video explains some of the most common issues with the Subaru Forester, including the transmission and engine: 57sGear GazetteYouTube · Oct 23, 2025

Is it difficult to replace spark plugs yourself?

Yes -- many people can and do change spark plugs themselves. It's a straightforward maintenance task for most gasoline engines when you have basic tools, a clear workspace, and follow correct procedures. Suitability depends on vehicle design, mechanical skill, and tools.

How long does it take to change spark plugs on a Subaru Forester?

If you have multiple socket extension sizes and the correct spark plug socket, 30-60 minutes the first time you do it. If you don't have the correct tools then however long it takes for you to take it to somebody who does.

Why are Subaru spark plugs so expensive?

Subaru spark plugs are expensive due to the significant labor involved in replacing them and the cost of the specialized, long-life iridium spark plugs used in most models. The unique boxer engine configuration places the spark plugs on the sides, requiring mechanics to lift the engine or partially disassemble other components to access them. This difficulty and the use of high-quality parts drive up the total cost.
 
Labor costs

• Difficult access: The boxer engine's flat, opposed cylinders mean spark plugs are located low down near the frame rails, unlike many inline engines where they are on top.
• Time-consuming replacement: Accessing the plugs can require significant labor, such as unbolting the engine from its mounts and carefully lifting it slightly to create enough space.
• Increased hourly rates: The extended time needed for the job results in higher overall labor costs from dealerships or independent mechanics who charge by the hour. 

Part costs

• Premium materials: Subaru uses premium iridium or platinum spark plugs, which are more expensive than standard copper plugs but offer a longer lifespan, often exceeding 100,000 miles. 
• Precise manufacturing: These plugs are manufactured with high precision to meet Subaru's specific engine requirements, which adds to their cost. 

Other factors

• Bundled services: Dealerships sometimes bundle spark plug replacement with other maintenance tasks for the 60,000-mile service, making the final bill appear higher. 
• Dealer markup: While the parts themselves are more costly, the primary reason for the high price is the labor involved, and dealership labor rates are often higher than those at independent shops.