Moroso Performance Engine Parts

Moroso is the brand most Subaru owners reach for when stock fluid-handling parts give up. If you are shopping this page, the best Moroso part is the one that fixes your weakest link: an aluminum expansion tank for cars with brittle factory tanks, a wet-sump pan with pickup and windage tray for hard cornering, or a small-body air-oil separator for 2015–2021 WRX street builds.

What These Parts Do and What to Look For

Moroso’s Subaru lineup centers on three jobs: cooling, oiling, and crankcase ventilation. The aluminum coolant expansion tanks replace the factory plastic tank that cracks with age and heat cycles; the wet-sump steel oil pans add pickup, windage tray, and 6-quart capacity for steadier oil control; and the air-oil separator kits keep oil mist out of the intake on turbo EJ and FA engines. Fabricated aluminum pieces like the fuse box cover round out the underhood cleanup.

When you shop, match fitment to your exact year and model — the listings are split by generation (02–07 WRX/STI, 08–20 WRX/STI, 15–21 WRX) — and pick the AOS body size that suits your bay. Aluminum construction is the theme across the line: it holds pressure, resists heat, and outlasts plastic.

About Moroso

Moroso built its name in motorsport oil control, where keeping oil where it belongs under hard cornering and acceleration is the difference between a finish and a failure. That racing background shows in the details of this collection: oil pans that ship with the pickup and windage tray engineered together, not as afterthoughts, and expansion tanks fabricated from aluminum instead of molded plastic. For Subaru owners, the practical result is straightforward — the parts address the exact weak points turbocharged EJ and FA engines are known for: oil control under lateral load and crankcase blow-by on boost.

The collection reads like a maintenance upgrade list for a high-mileage or hard-driven Subaru. Coolant system hardware sits next to oil system hardware because the two fail on similar timelines in tuned cars. If you are cross-shopping, our Oil System, Oil Pans, Oil Coolers, and Cooling collections carry complementary parts, and Radium Engineering is another motorsport-grade option worth a look.

Moroso FAQ

Do I need a tune for a Moroso expansion tank or oil pan?

No. These are hardware upgrades — they change how fluids are contained and controlled, not how the engine breathes or fuels, so no tuning is required.

What is the difference between the small-body AOS and a larger one?

The small-body kit is sized for tighter engine bays and street-level builds, like the 15–21 WRX listing shown here. Larger separators handle more blow-by on high-power builds. Pick by your power level and available space, and check your year and model.

Why aluminum instead of plastic for an expansion tank?

Factory plastic tanks go brittle with heat cycles and eventually crack or weep. Aluminum holds pressure cycle after cycle and is the standard fix for aging cooling systems.

Will the Moroso oil pan fit my car?

The wet-sump pan listing covers EJ20, EJ22, and EJ25 engines with 6-quart capacity. Verify your exact model year against the listing before ordering — check your year and model.

Related reading: Enhanced Airflow and Cooling: The Benefits of Upgrading Your WRX Grille for Performance.