The 2015 Forester uses a cartridge-style oil filter mounted on top of the engine

The 2015 Subaru Forester does not have a spin-on oil filter like many other vehicles. Instead, it uses a cartridge filter — a cylindrical element that sits inside a plastic housing on the top of the engine. The housing is a white or translucent plastic cap with a large center bolt. This design means you cannot straightforward unscrew and replace a filter; you must open the housing, remove the old element, and install a new one.

The cartridge filter is located directly above the engine block, toward the passenger side. It is one of the most visible components on top of the engine and is impossible to miss once you open the hood. Because it sits high and exposed, it is easier to access than spin-on filters on many other vehicles, though you will still need to drain some oil from the housing when you open it.

Key Takeaways

  • The 2015 Forester has a cartridge-style filter in a plastic housing on top of the engine, not a spin-on filter underneath.
  • You will need a filter wrench to remove the center bolt of the housing — a standard 86 mm or 3.3 inch socket wrench works, or a dedicated cartridge filter wrench.
  • The correct replacement filter is Subaru part number 16510AA051 or equivalent OEM and aftermarket cartridge filters designed for this model year.
  • Changing the filter takes 10 to 15 minutes once you have the right tools and does not require lifting the vehicle.
  • You must replace the rubber O-ring seal on the housing cap every time you change the filter to prevent oil leaks.

What tools and parts you need

To change the oil filter on a 2015 Forester, you need an 86 mm cartridge filter wrench or a standard 86 mm socket wrench to remove the center bolt of the housing. Many auto parts stores stock dedicated cartridge filter wrenches that fit this size. If you use a socket wrench, make sure it is 86 mm (approximately 3.3 inches) — using the wrong size will round off the bolt and make removal difficult or impossible.

You will also need a new cartridge filter element and a replacement O-ring seal. Subaru part number 16510AA051 is the OEM filter for the 2015 Forester. Many aftermarket brands also make cartridge filters for this model, including Fram, Bosch, and Mobil 1. The O-ring usually comes with the new filter, but if it does not, Subaru part number 16510AA000 is the correct seal. Have an oil drain pan ready — you will spill a small amount of oil when you open the housing.

Step-by-step replacement process

Start with a warm engine (not hot). Warm oil drains faster and more completely than cold oil. Open the hood and locate the white plastic filter housing on top of the engine. Place your oil drain pan underneath it to catch spilled oil.

Use your 86 mm wrench to turn the center bolt counterclockwise. Turn slowly at first — the bolt is tight and you do not want to slip and damage it. Once it breaks loose, you can turn it by hand. Remove the bolt completely and set it aside. Lift the plastic housing cap straight up and away from the engine. Oil will drip from the housing and the old filter element, so keep the drain pan positioned underneath.

Remove the old cartridge filter element from inside the housing. It will be wet with oil. Inspect the rubber O-ring seal on the underside of the plastic cap. If it is cracked, hardened, or visibly damaged, replace it with a new one. If it looks intact, you can reuse it, but Subaru recommends replacing it every time you change the filter to prevent leaks.

Wipe the inside of the plastic housing clean with a lint-free cloth or paper towel. Remove any debris or old rubber particles. Insert the new cartridge filter element into the housing, making sure it sits flat on the bottom. The element should not be forced — it should slide in smoothly. Place the plastic cap back on top of the engine, aligning the center hole. Thread the center bolt back in by hand first, then tighten it with your wrench. Tighten firmly but do not over-tighten — you are sealing a rubber O-ring, not a metal-to-metal joint. A quarter turn past hand-tight is usually enough.

Start the engine and let it run for 30 seconds. Check underneath the housing for any oil drips. If you see oil leaking from around the cap, turn off the engine, let it cool for a minute, and tighten the center bolt another quarter turn. If the leak stops, you are done. If it continues, the O-ring may be damaged or installed incorrectly — remove the cap and check.

OEM versus aftermarket cartridge filters

Subaru's original equipment manufacturer (OEM) filter, part number 16510AA051, costs between $12 and $18 depending on where you buy it. Aftermarket cartridge filters from brands like Fram, Bosch, and Mobil 1 typically cost $8 to $15 and meet the same performance standards. Both OEM and quality aftermarket filters will protect your engine equally well.

The main difference is brand consistency and warranty. OEM filters come with Subaru's backing and are may provide to fit without modification. Aftermarket filters are made by third-party manufacturers but are engineered to the same specifications. If you are unsure whether an aftermarket filter will fit, check the product description or call the parts store — they can confirm compatibility with your 2015 Forester before you buy.

Common mistakes to avoid

The most common error is forgetting to replace the O-ring seal on the plastic cap. If you reuse an old, hardened O-ring, oil will leak from the housing even if the bolt is tight. The seal costs less than $2 and takes five seconds to swap out — always replace it.

Another mistake is over-tightening the center bolt. The bolt threads into the plastic housing, not into metal. Over-tightening can crack the plastic or damage the threads, making the housing unusable. Tighten until snug, then stop. If you have already over-tightened and the bolt spins freely without tightening, the housing threads are stripped and the cap will need to be replaced.

Do not confuse the oil filter housing with the oil drain plug. The drain plug is located on the underside of the engine and is a separate bolt. The filter housing is the white plastic cap on top. If you are changing the oil at the same time, drain the oil first, then change the filter.

When to change the oil filter

Subaru recommends changing the oil filter every time you change the engine oil. For a 2015 Forester with standard driving, that is every 6,000 miles or every six months, whichever comes first. If you drive in severe conditions — frequent short trips, towing, or dusty environments — Subaru recommends every 3,000 miles or three months.

You can check your specific maintenance schedule in your owner's manual, which will list the exact interval for your driving conditions. The filter element cannot be cleaned or reused — it must be replaced each time. A clogged filter restricts oil flow and can damage the engine, so do not skip this step or extend the interval beyond what Subaru recommends.

Frequently Asked Questions

Can I change the oil filter without changing the oil?

Yes. The filter and oil are separate maintenance items. You can change the filter alone if you want, though most people change both at the same time since you are already working on the engine. If you change only the filter, you will still lose a small amount of oil from the housing, so check your oil level afterward and top it up if needed.

What size wrench do I need for the center bolt?

You need an 86 mm wrench. This can be a socket wrench, a cartridge filter wrench, or an adjustable wrench set to 86 mm. Do not guess at the size — using a wrench that is too small or too large will slip and damage the bolt. If you do not have an 86 mm wrench, most auto parts stores will loan or rent one for free or a small deposit.

Is the O-ring really necessary to replace every time?

Subaru's official recommendation is to replace it every time. In practice, if the O-ring looks clean and flexible, it can last two or three oil changes. However, a new O-ring costs less than $2 and takes five seconds to install. The cost of replacing a cracked housing due to a failed seal is much higher, so replacing the O-ring is the safer choice.

What should I do with the old filter element?

The old cartridge filter element can be placed in your regular trash. It contains oil residue but is not classified as hazardous waste in most jurisdictions. If you want to recycle it, some auto parts stores accept used filters, though they typically do not charge you for disposal. Check with your local store.