Is it hard to change spark plugs in a Subaru?
Not especially for a capable DIYer, but it can be more challenging on certain Subaru engines. For many four-cylinder Subarus, a spark plug swap is doable in about one to two hours with the right tools. Turbocharged or rear-bank plugs in some models can extend the process due to tighter spaces and additional components.
Understanding the layout can affect the difficulty
Subaru engines use a boxer (flat) layout with coil-on-plug ignition in most modern four-cylinders. Access to plugs varies by model: some engines let you reach the front and rear plugs from the top with minimal disassembly, while others require removing parts such as the intake plenum or supplementary hoses to access rear plugs. The job tends to be straightforward on non-turbo engines but can be noticeably more awkward on turbocharged or older designs where tight confines and heat make removal and installation slower.
Before diving into any spark plug replacement, it helps to know your exact engine code (for example, EJ-series or FA/FB-series) and consult your owner's manual or a service guide for torque specs, gaps, and any model-specific cautions. This ensures you use the correct parts and procedures for your Subaru.
Gathering the right information and tools beforehand can save time and reduce the risk of cross-threading or damaged ignition components. Below is a practical checklist and a step-by-step guide tailored to Subaru engines.
Below is a practical checklist and guide to help you determine whether this is a DIY job for you and how to approach it safely and efficiently.
Tools and parts you’ll typically need, plus a plan for a smooth job.
- Correct spark plugs for your engine (iridium/platinum, appropriate heat range and gap p. autoparts guidance or service manual).
- Spark plug socket (usually 5/8 inch or 16 mm) with a magnetic insert
- Ratchet, extensions, and a swivel or wobble extension for tight spaces
- Torque wrench to meet the manufacturer's specified tightening torque
- Coil-removal tool or small flat-head/trim tool to release coil connectors, plus gloves or eye protection
- Dielectric grease for coil boots (optional but helpful for a clean, stable connection)
- Small pick or magnet for retrieving dropped fasteners (optional)
- Light source or a work lamp to see into tight spaces
- Anti-seize compound (generally not recommended on modern Subaru plugs due to torquing behavior; consult your manual)
- Lubricant or penetrating oil for stubborn boots or plugs (sparingly)
- Safety gear: gloves, eye protection, and disconnecting the battery before starting
Having the right toolkit and parts on hand helps keep the job steady and reduces surprises in a cramped engine bay.
Step-by-step procedure for replacing spark plugs in a Subaru
Before starting, ensure the engine is cold and you’re in a well-lit, stable workspace. This step-by-step outline covers a typical four-cylinder Subaru with coil-on-plug ignition. Some models may require additional steps for rear-bank plugs or intake-manifold removal; consult your service guide for model-specific nuances.
- Disconnect the negative battery cable to prevent any accidental short or shock while working near electrical components.
- Remove the engine cover if your model has one, to expose the coil packs and spark plug wells.
- Identify each coil pack and its electrical connector. Gently disconnect the connector and move the coil aside without pulling on the wiring harness.
- Remove the ignition coil/boot from each cylinder one at a time to access the spark plug. Do not twist excessively; lift straight up to avoid damaging the coil boot.
- Use a spark plug socket with extension to reach into the plug wells and carefully unscrew the old spark plug. Keep the plug if you’re inspecting it for wear, or discard and replace with a new one that matches your engine’s specification.
- Check the plug gap on the new plug (or rely on manufactured pre-gap) and thread it in by hand to avoid cross-threading. Once finger-tight, snug and then torque to the vehicle’s specification using a torque wrench.
- Reinstall the ignition coil/boot over the new plug. Apply a thin coat of dielectric grease to the inside of the boot if desired to improve electrical contact and ease future removal.
- Repeat the process for each cylinder. After all plugs are replaced, reinstall any removed components (coil covers, intake pieces, engine cover) and reconnect the negative battery cable.
- Start the engine and listen for smooth idle. If you notice misfires or rough running, double-check that all boots are seated properly and that each electrical connector is fully engaged.
The level of difficulty can vary depending on whether your model has exceptionally tight rear-bank access or requires removing parts such as the intake manifold. In those cases, the process can take longer and may benefit from extra hands or professional help.
Model-specific considerations
Engine families differ in how accessible the plugs are. In most non-turbo Subarus with the EJ-series four-cylinders, plugs tend to be more accessible from the top, though rear plugs can still be a challenge. The FA/FB-series engines (including turbocharged Subarus like the WRX) place coils directly on the plugs, so you’ll be dealing with coil removal for each plug and, in some configurations, tighter spaces around the intake and turbocharger components. Always verify the exact procedure for your model year and engine code before starting.
When to consider hiring a pro
If the rear-cylinder plugs require removing the intake manifold, or if you’re dealing with a high-mileage engine with stubborn boots or damaged coil boots, the job becomes more intricate. In these cases, a professional shop can save time and reduce the risk of damage to ignition coils, boot seals, or the threads in the spark plugs.
Summary
For many Subaru owners, replacing spark plugs is a feasible DIY task that rewards careful preparation, correct parts, and a methodical approach. The main variable is engine design: most four-cylinder Subarus offer straightforward top-access plugs, but turbocharged or rear-bank plugs can demand more space and additional disassembly. Plan for about one to two hours for a standard job, longer for tight spots or unfamiliar setups, and always consult your model’s service manual for precise torque specs and gap settings. If you’re unsure, enlisting professional help is a prudent option to ensure reliability and avoid damage.
