There’s a likely probability you will need to replace your set of spark plugs several times during your ownership of a 2015 Subaru Legacy. Spark plugs are one of the most critical components inside your engine as they begin the entire combustion process that starts and keeps your engine running for many thousands of miles. Like most engine parts, spark plugs experience wear over time and eventually need replacement, but fortunately this is a repair you can do yourself. Odds are, if you’ve found yourself here, you have no idea how to do that, or perhaps you’d just like to know what kind of spark plugs you need to buy. The entire process of changing your spark plugs should take roughly 20-45 minutes. This article will go over everything you’ll need to know about your Subaru Legacy’s spark plugs, whether you need some general information or a full, step-by-step guide to performing a spark plug change.
Correct spark plugs on a 2015 Subaru Legacy
Recommended 3.6L H6 2015 Subaru Legacy Spark Plugs
Recommended 2.5L H4 2015 Subaru Legacy Spark Plugs
These spark plugs are an exact fit for their respective engines and will match the required specifications. Make certain that you purchase the correct quantity of spark plugs for your engine corresponding to the number of cylinders. Sometimes manufacturers will bundle spark plugs in quantities that make it difficult to buy the exact amount you need for your engine. In this case, it is a good idea to purchase enough for your next two spark plug changes just so you will always have a new set ready to go. We always try to recommend the best possible spark plugs for the money, and these spark plugs are either a factory recomendation or an equivalent replacement available in today’s market at a reasonable price.
How often should I change my spark plugs?
Very generally, it is advised that you replace spark plugs once every 20,000 to 40,000 miles. Of course, please make sure to check your owner’s manual to determine the specific interval determined by Subaru for the 2015 Legacy. Of course, if you drive your vehicle more aggressively or own a Legacy with some modifications, you may want to consider changing your spark plugs closer to the 20,000 miles end of that spectrum.
However, there are also classic signs of a car that may potentially need a spark plug replacement early, such as:
- Problems starting your engine
- Rough idle
- Engine misfiring
Note that this list is absolutely not comprehensive, and these problems on their own do not definitively point to the spark plugs being the solitary culprit. However, the best way to prevent any issues with your vehicle is to take care of it with regular maintenance, and you are definitely doing so with the responsible decision to replace your Subaru Legacy’s spark plugs on a regular basis.
Changing spark plugs on a 2015 Subaru Legacy
This is a process you should be able to do on your own with some commonplace garage tools. Of course, consult your owner’s manual, as well as a factory service manual (FSM for short) or an equivalent Haynes or Chiltons manual. The video shown below does a good job of outlining the process.
Helpful Tools
- A spark plug gap tool. This allows you to check the gap of your spark plugs and modify it if necessary. Most plugs will come pregapped, but if this is not the case, you should for sure have one of these.
- I also highly recommend you have a feeler gauge as it makes it a bit easier to check the exact gap, and it comes in handy for countless other jobs.
- A set of spark plug sockets – These come in extremely handy because many standard sockets are not deep enough for spark plugs. Additionally, some spark plug holes are a bit smaller, so it requires a thinner wall like the one featured in the product here to fit. The linked product also features a magnet to keep a good hold of the spark plug so you do not drop it into your engine bay!
- A torque wrench is a very important tool to have in your garage. You should check your FSM (factory service manual) to determine the correct torque rating to use when putting in the new spark plugs for your 2015 Subaru Legacy to be certain they are installed properly.
- A spark plug tester – this is definitely a niche tool, but it can save you lots of time. Although we’ve discussed spark plug replacement being a good thing to replace regularly and not just when issues occur, you may also be replacing your spark plugs because of a problem. This tool can help you diagnose the definite problem.
Tips for changing spark plugs on your 2015 Subaru Legacy
- During this process, one of the most vital things to ensure you do is to avoid overtightening the plugs or worse, cracking them due to overtightenting. Use a torque wrench capable of lower, more precise torque ratings to be sure that you don’t make this mistake.
- Your engine should be completely COLD before you replace your spark plugs. Ensure you wait at least 30 minutes after your engine has been running before attempting to replace the spark plugs on your 2015 Subaru Legacy
- Before starting, disconnect the negative terminal of your battery. It is wise to disconnect the battery anytime you work on the electrical system of your Subaru Legacy or any other vehicle.
- Note that this is not official advice as many spark plug manufacturers advise against the use of anti-seize. However, I have heard from numerous old-school mechanics that they always apply a tiny amount of anti-seize to the threads of their spark plugs, especially on older vehicles.
- It’s not a bad idea to use dielectric grease when installing new spark plugs. You can apply a a little bit to the inside of the boot and the ceramic part of your spark plugs. It lessens the chance of voltage leak and helps avoid the misfortune of the boot fusing to the spark plug over time.