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Choosing the right oil pump for your WRX STI isn’t just about stopping a leak—it’s about keeping oil pressure where it needs to be so your EJ25 doesn’t starve under boost. A pump that flows too little risks bearing wear on a built motor, and one that’s not genuine can fail at the front seal, dumping oil fast. This guide cuts through the fitment confusion to land on the pumps owners actually trust for daily driving and high-horsepower builds alike.
I’m Mo Maruf — the founder and writer behind GoCarLife. This guide is built by comparing the manufacturers’ published specifications and the patterns across verified customer reviews, so you get each pick’s real strengths and trade-offs instead of marketing spin.
Whether you’re refreshing a stock long block or upgrading a modified short block, finding a reliable wrx sti replacement oil pump means matching flow rate, genuine OEM construction, and a complete seal kit to avoid the common leak headaches buyers report.
Our Picks at a Glance
How To Choose The Best WRX STI Replacement Oil Pump
Picking the right pump for your EJ25 depends on three things: flow volume, genuine casting quality, and whether you get the seals you need in the box. Here is what each one means for your install.
Flow Volume — 10mm vs 11mm Rotor
The measurement refers to the width of the rotor gear inside the pump. A 10mm pump is the factory standard for the WRX STI and is perfectly adequate for a stock or lightly modified engine. An 11mm pump moves more oil volume per revolution, which helps maintain oil pressure in high-RPM, high-boost builds with larger bearing clearances. The trade-off is that an 11mm pump can cavitate (draw air) at very high RPM if the oil pickup is restrictive, so it pairs best with an aftermarket pickup tube. Owners mention that the 11mm pump is a “great upgrade over the 10mm pump” for modified Subaru engines.
Genuine OEM vs Aftermarket Casting
Subaru’s factory oil pumps are cast and machined to tight tolerances, with quality indicators like blue dot QA marks and smooth casting surfaces. Aftermarket pumps can sometimes have oversized casting tabs that interfere with the oil cooler pipe bracket, or a crank angle sensor boss that doesn’t align right. The genuine part is heavier and uses JIS hardware, and the seal bore is machined to the correct diameter. The data shows that aftermarket front crank seals are a known failure point, with one owner losing 2.5 quarts per 100 miles from an undersized seal.
Complete Kit vs Bare Pump
A bare pump means you still need to source the crank seal, the O-ring for the block face, and the seven pump bolts separately. Some pumps ship with no sealant and no gasket—you must buy your own RTV. A complete kit that includes the crank seal, O-ring, and bolts saves you a second parts run and ensures you have the correct seal profile. Owners note that the kit “contained exactly what I needed”.
Quick Comparison
| Model | Best For | Rotor Width | Weight | Included Seals | Amazon |
|---|---|---|---|---|---|
| Subaru 11mm Oil Pump★ Best Overall | Built / High-boost EJ25 | 11mm | Not specified | Bolts & seals included | Amazon |
| Genuine Subaru 15010AA360 | Budget-friendly OEM swap | 11mm | 1 lb | Not included | Amazon |
| DNJ OP706 | Budget non-turbo Subaru | Standard volume | 2.1 lb | Not included | Amazon |
| Genuine OEM 10mm Subaru Kit | Stock / Daily driver STI | 10mm | 3.16 lb | Full kit: seal, O-ring, 7 bolts | Amazon |
In‑Depth Reviews
1. Subaru 11mm 2.5L Oil Pump w/Bolts & Seals
Our pick — over 4.5★ from 80+ verified ratings; the strongest balance of quality and price.
The go-to 11mm upgrade that bolts on and holds oil pressure for modified Subaru engines.
If you are building a stronger STI short block or swapping a turbo motor into a Forester XT, this is the pump owners reach for. It is a genuine Subaru 11mm pump, which moves more oil than the stock 10mm unit, and the box includes the bolts and seals so you do not have to hunt for the seven pump bolts separately. Owners confirm it “fits perfectly on the STI short block” even in a swapped chassis, and after a full year of use the consensus is that it is “highly recommended for oil flow and lubrication” when paired with an improved oil pickup. The only thing to remember is that you still need to supply your own RTV sealant for the block face—the kit does not include it.
Built-Motor Ready
- Genuine Subaru 11mm rotor for higher oil volume than the factory 10mm
- Complete kit with seven bolts and crank seal included
- Factory sealed packaging with verified OEM casting quality
One Extra Step
- No sealant included—you must buy RTV separately
- 11mm pump can cavitate at very high RPM if not paired with an upgraded pickup
Reach for this if: your EJ25 has a built bottom end, bigger turbo, or higher rev limit that needs the extra oil volume an 11mm pump provides.
Look elsewhere if: your engine is 100% stock and you prefer a simpler drop-in with no pickup upgrade needed.
2. Genuine Subaru Parts – Oil Pump Ay Engine 15010AA360
A proper 11mm OEM pump that costs less than the aftermarket alternatives.
This is the same 15010AA360 part number found on genuine Subaru packaging, with the Subaru Japan markings, smooth casting, and JIS hardware that confirms it is a genuine factory piece. At just 1 pound, it is noticeably lighter than the full 3.16-pound kit above because it is the bare pump—no seals, no bolts, no O-ring. What makes it a value standout is the price: buyers call it a “legit OEM oil pump at a surprisingly low price” and confirm it is an 11mm pump that works as a “great upgrade over the 10mm pump.” The OEM quality is the top praise among owners, and the value-for-money score is strong. You will need to source the crank seal and pump bolts separately, but if you already have a stash of Subaru seals or want to pick your own brand of aftermarket seal, this is the most cost-effective way to get a genuine 11mm rotor.
OEM Price Break
- Genuine Subaru 11mm pump confirmed by Japan markings and part number
- Weighs only 1 pound—much lighter than the full kit
- Owners praise the OEM quality and the lower price versus dealer
Bare Bones
- No crank seal, O-ring, or bolts included—bring your own
- Not a true drop-in unless you already have seal parts on hand
Best if: you want the genuine Subaru 11mm casting without paying for a full seal kit you don’t need.
Not ideal if: you want one box with everything needed to button up the front of the engine.
3. DNJ OP706 Oil Pump Housing for 1990-2015 Subaru
A low-cost aftermarket option, but one that demands careful seal and fitment attention.
This DNJ pump covers a wide range of Subaru and Saab 9-2X models from 1990 through 2015, and at 2.1 pounds it sits between the bare OEM pump and the full kit in heft. The price is the main draw—it undercuts the genuine Subaru options significantly. However, the buyer experience is a mixed bag. Several customers note that the front crank seal fails soon after installation, with one describing a loss of 2.5 quarts per 100 miles. Another found the casting tab for the oil cooler pipe mount was oversized, requiring grinding to fit the bracket, and the crank angle sensor needed shimming. The consensus among those who had issues is to buy a good aftermarket seal kit separately and inspect the casting carefully before installation. It pumps oil and maintains pressure when everything lines up, but the fitment margin is tighter than an OEM piece.
Wallet Friendly
- Lowest upfront cost in this roundup
- Broad vehicle coverage: Subaru Baja, Forester, Legacy, Outback, Impreza, Saab 9-2X
- Maintains oil pressure when seal and casting align
Known Pitfalls
- Front crank seal reported undersized—may leak heavily; buy a quality replacement seal from Napa or Subaru
- Casting tab for oil cooler pipe may need grinding to fit
- Crank angle sensor may need shimming; not a true bolt-on for every application
Consider this if: budget is the primary factor and you are comfortable doing pre-install fitment checks and supplying your own seal kit.
skip it if: you want a guaranteed bolt-on experience without grinding or shimming.
4. Genuine OEM Subaru 10mm Oil Pump w/Seal & O-Ring Bolts
The everything-in-the-box kit for a stock STI that needs a leak-free, low-maintenance install.
This is the most complete package you can buy for a factory-spec replacement. It includes the genuine Subaru 10mm pump (part 15010AA300), seven pump bolts (800706500), the oil pump seal (10991AA000), and the crank seal (806733030)—all genuine Subaru items. At 3.16 pounds, it is the heaviest kit here because of the hardware and seals. For a stock or lightly modified WRX STI daily driver, the 10mm rotor is exactly what Subaru engineered for the car, and the complete seal package means you avoid the “failed front crank seal” headache that some aftermarket pumps cause. Owners describe it as a “complete package” that “contained exactly what I needed” and note that after installation there are “no runs, drips or errors.” The only thing the box does not contain is RTV sealant—buy a tube of the correct grey silicone before you start the job.
Total Drop-In Package
- Genuine Subaru 10mm pump—the exact factory-spec part for a stock STI
- Includes crank seal, pump O-ring, and all seven pump bolts
- Heavier construction (3.16 lb) with OEM casting quality; owners call it “perfect”
Know Before You Install
- Still need to buy RTV sealant—not included
- 10mm rotor is not ideal for high-boost builds that need extra oil volume
Choose this for: a stock-block STI or a daily driver refresh where you want one box with every OEM part to stop leaks.
Not for: a built motor running 25+ psi where the 11mm flow advantage becomes necessary.
Understanding the Specs
Rotor Width — 10mm vs 11mm
This is the thickness of the pump’s inner rotor. A wider rotor displaces more oil per turn, raising oil pressure and volume. Stock STI engines use a 10mm pump. Built engines with larger bearing clearances or higher RPM need the 11mm to keep bearings fed. Too much pump for a stock engine can aerate the oil at high RPM if the pickup is restrictive.
Complete Kit vs Bare Pump
A bare pump is just the housing and rotor—you supply the crank seal, O-ring, and bolts. A complete kit bundles all of those parts and sometimes the pump bolts. Choosing a bare pump saves money but risks a seal mismatch that can cause an oil leak days after installation. Owners who bought a bare pump and a cheap seal ended up losing quarts of oil per 100 miles.
FAQ
Will an 11mm oil pump hurt my stock STI engine?
Do I need to buy a separate seal kit with the genuine OEM pump?
What RTV sealant should I use for the oil pump install?
How do I know if my oil pump is failing?
Will a 10mm pump fit a 2015 STI?
Can I use an aftermarket pump on a daily driver Subaru?
How much heavier is the full OEM kit compared to a bare pump?
Will a DNJ pump work on a 2004 WRX?
Final Thoughts: The Verdict
For the majority of shoppers, the wrx sti replacement oil pump winner is the Subaru 11mm 2.5L Oil Pump because it delivers the extra flow a modified EJ25 needs and arrives with all the bolts and seals. If you are refreshing a stock daily driver, the Genuine OEM 10mm Kit is the leak-proof, complete package. And for a tight budget where you are comfortable doing fitment checks, the DNJ OP706 gets the job done if you supply your own quality seal.
How We Picked
We do not accept paid placement. Every pick is matched to a real buyer and a real use-case; we do not hands-on test units.
Sources & Methodology
Specifications: manufacturer listings and product documentation. Review insights: verified customer reviews, as of July 2026. Pricing: not shown on this page (it changes often); check the current price via the retailer link.
As an Amazon Associate, GoCarLife earns from qualifying purchases. This does not affect which products we feature.