Maintaining your vehicle is an incredibly rewarding task and learning how to replace your spark plugs is a great place to start. There’s a decent chance you will need to replace your old spark plugs several times during your ownership of a 2004 Subaru Impreza. Spark plugs are one of the most vital parts inside your engine as they start the entire combustion process that starts and keeps your engine running for many thousands of miles. Similar to most engine components, 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 maybe you’d just like to know what kind of spark plugs you need to buy. The complete process of changing your spark plugs should take roughly 20-45 minutes. This article will go over everything you will need to know about your Subaru Impreza’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 2004 Subaru Impreza
Recommended 2.5L H4 2004 Subaru Impreza Spark Plugs
Recommended 2.0L H4 Turbocharged 2004 Subaru Impreza Spark Plugs
Recommended 2.5L H4 Turbocharged 2004 Subaru Impreza Spark Plugs
These spark plugs are an exact fit for their respective engines and will match the required specifications. As this 2004 Subaru Impreza features a 4 cylinder engine, ensure you purchase 4 spark plugs. 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 now 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 2004 Impreza. Of course, if you drive your vehicle more aggressively or own a Impreza 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 needs a spark plug replacement prematurely, such as:
- Rough idle
- Problems starting your engine
- Engine misfiring
Note that this list is absolutely not comprehensive, and these problems on their own do not necessarily point to the spark plugs being the standalone culprit. However, the best way to prevent any issues with your vehicle is to take care of it with organized maintenance, and you are definitely doing so with the responsible decision to replace your Subaru Impreza’s spark plugs on a regular basis.
Changing spark plugs on a 2004 Subaru Impreza
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.
As noted before, you should be able to complete a spark plug change with some ordinary tools you most likely already have. However, there are a few tools that are specific to this job that you may not have, and we also want to recommend some commonplace tools that you should definitely have in your toolbox if you don’t already.
- A torque wrench is a very important tool to have in your garage. You will want to check your FSM (factory service manual) to determine the correct torque rating to use when inserting the new spark plugs for your 2004 Subaru Impreza 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 an issue. This tool can help you diagnose the definite problem.
- 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 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 not, you should absolutely have one of these.
- I also highly recommend you have a feeler gauge as it makes it a bit more straightforward to check the exact gap, and it is helpful for countless other jobs.
Tips for changing spark plugs on your 2004 Subaru Impreza
Be sure to reference the video above before you attempt to repair the spark plugs on your 2004 Subaru Impreza, as well as review your FSM (factory service manual) or owner’s manual. Be sure to check the tips shown here to help you as you complete this repair.
- It isn’t a bad idea to use dielectric grease when installing new spark plugs. You can apply a small amount to the inside of the boot and the ceramic part of your spark plugs. It prevents voltage leak and helps avoid the misfortune of the boot fusing to the spark plug over time.
- 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.
- Before starting, remove the negative terminal of your battery. You should always disconnect the battery anytime you work on the electrical system of your Subaru Impreza or any other vehicle.
- Your engine should be completely cold before you replace your spark plugs. Wait at least 30 minutes after your engine has been running before attempting to replace the spark plugs on your 2004 Subaru Impreza
- 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 light coating of anti-seize to the threads of their spark plugs, especially on older vehicles.