KOYORAD Radiator for Subaru WRX & STI

Critical Fitment Note Before You Order

KOYORAD radiators for the 2002–2021 WRX/STI are manual transmission only. The Hyper V-Core design does not include the internal transmission cooler that auto-trans WRX/STI models require. Automatic owners can fit the same radiator only with the addition of an external auxiliary transmission cooler — get in touch before ordering if you're running an auto so we can spec the supporting parts properly.

Chassis & Engine Fitment

• GD chassis (2002–2007) — KOYORAD VH091672: Subaru Impreza WRX 2003–2007, WRX STI 2004–2007 (EJ205/EJ207/EJ255/EJ257)
• GR/GV/GH/VA chassis (2008–2021) — KOYORAD VH091662: Covers 2008–2014 WRX (EJ255), 2008–2021 STI (EJ257), 2015–2021 WRX (FA20F), 2005–2012 Legacy GT (EJ255), 2005–2009 Outback XT, 2009–2013 Forester XT, 2013–2017 Crosstrek 2.0L
• 2002 model year WRX: Requires the 2002-specific radiator (VH090866) — verify your factory radiator has a radiator cap before ordering. Early WRX without a radiator cap need the specific 2002 unit

Why the EJ & FA Subarus Need a Radiator Upgrade

The factory Subaru cooling system on the EJ-series turbo and FA20F engines is adequate for stock-tune commuting and not much else. Three things conspire against it:

1. Engine bay packaging. Subaru's symmetrical AWD layout pushes the engine forward over the front axle, and the boxer four-cylinder spreads heat across a wider package than an inline engine. The factory radiator sits in a tighter space than most turbocharged four-cylinder cars get, and the airflow path through the front of the car is constrained by the intercooler and air ducting.

2. Plastic end tanks. Like most OEM radiators, the factory Subaru unit uses aluminium core construction with plastic end tanks. The tank-to-core seam is the universal failure point on these radiators — repeated heat cycling makes the plastic brittle, and after 8–12 years the seam starts weeping coolant, eventually cracking and dumping coolant under load. Almost every GD-chassis WRX/STI in Australia is now in that danger zone. The 2008–2014 cars are entering it.

3. Aftermarket power. A tuned WRX or STI generates significantly more heat than the factory radiator was sized to dissipate. The classic symptom is "fine on the street, runs hot on a track day or summer hill climb" — the factory radiator simply runs out of thermal headroom when the cooling demand goes up. ECU-controlled timing pull masks this for a while, but the underlying problem is undersized cooling capacity.

The KOYORAD Hyper V-Core addresses all three: full aluminium construction (no plastic to fail), 36mm dense core with hyper fin/tube density for maximum heat transfer in the tight Subaru engine bay, and significantly greater cooling reserve for tuned cars.

The Hyper V-Core Design

KOYORAD developed the Hyper V-Core series specifically for cars like the WRX/STI — modern turbocharged platforms with limited engine bay space where the factory inlet and outlet positions don't allow KOYORAD's N-Flo internal partition design. The Hyper V-Core's answer is to maximise heat transfer area in the same physical footprint as the factory radiator, using a 36mm thick core with significantly higher fin and tube density than standard radiator designs.

Specifications for the GR/VA chassis VH091662:

• Core: 36mm Hyper V-Core, full aluminium construction
• Dimensions: Core depth 1.41", core height 13.38", core width 26.65"
• Weight: 12.1 lbs (~5.5kg) — significantly lighter than OEM
• Construction: Hand TIG-welded end tanks, Nocolok-brazed core, billet machined filler neck
• Optional accessory port: M14-1.25 thread for aftermarket sensor
• Transmission: Manual transmission only (no internal trans cooler)

Specifications for the GD chassis VH091672:

• Core: 36mm Hyper V-Core, full aluminium construction
• Dimensions: Core depth 1.40", core height 13.40", core width 25.50"
• Weight: 11.8 lbs (~5.4kg)
• Construction: Hand TIG-welded end tanks, Nocolok-brazed core, billet filler neck and 1/8 PT accessory port (plug included)
• Transmission: Manual transmission only

Installation Notes

The KOYORAD installs into the factory radiator position using OEM mounting points, OEM fan shroud bolt pattern and OEM hose locations. No cutting, no bracket modification, no relocation of supporting components.

Two practical things to know:

1. Upper radiator hose may require trimming. Because the Hyper V-Core sits in a slightly different position than the OEM radiator (mounting points are identical, but the thicker core changes the effective face of the radiator), the upper coolant hose sometimes needs to be shortened by 5–15mm for proper clearance. This is a 30-second cut with a fresh blade and is far less invasive than the modifications other thick-core radiators sometimes require.

2. Fan mounting clearance with aftermarket charge piping. The Hyper V-Core's fan mounting points sit roughly 12mm further forward than OEM. On cars with large-diameter aftermarket cold-side charge pipes routing past the passenger-side fan, the passenger fan can foul against the charge pipe. The fix is to remove the intercooler and charge pipe during fan installation, then reinstall the boost plumbing — five extra minutes during the install and you avoid the problem entirely.

3. Radiator cap not included. The KOYORAD ships without a cap because cap pressure ratings vary by build target. Most Subaru owners reuse the OEM cap (which fits the KOYORAD's filler neck), but for tuned or track cars we recommend the higher-pressure KOYORAD SK-C13 1.3 Bar cap as an upgrade.

How the WRX/STI KOYORAD Compares to Alternatives

The two main competing brands in the AU market for these chassis are Mishimoto and CSF. Here's the honest comparison for the Subaru specifically.

vs Mishimoto: Both are excellent radiators. KOYORAD's hand TIG-welded construction and Japanese engineering oversight is meaningful for buyers who value manufacturing detail. Mishimoto's lifetime warranty + accident protection is the strongest in the market and matters if long-term coverage is your priority. Pricing is broadly comparable on this platform.

vs CSF: CSF makes a strong WRX/STI radiator with their newest fin technology. Less common in the AU market than KOYORAD or Mishimoto. For the EJ platforms, KOYORAD's decades of Subaru-specific fitment experience is reflected in the install quality.

For a more detailed cross-brand comparison, see our KOYORAD vs Mishimoto vs CSF buyer's guide.

Build Path — Where the Radiator Fits

For most Subaru WRX/STI owners, the radiator upgrade earns its place at one of three points in a build:

Stage 0 — OEM radiator failure. If your factory radiator is showing signs of plastic-tank failure (weeping coolant, hairline cracks at the seam, slow coolant loss), replacing it with the KOYORAD is significantly better than replacing it with another OEM-spec unit. The aluminium construction means it won't fail again, and the upgrade is permanent. This is the most common reason GD-chassis owners install a KOYORAD.

Stage 1 — Stock turbo, supporting mods, no tune. If you're running the factory tune with bolt-on supporting mods (intake, downpipe, exhaust), the radiator probably isn't the most urgent upgrade — but it's a meaningful long-term investment. Adds cooling headroom for any future tuning.

Stage 2 — Tuned car, street/track use. Once you're running a proper tune (Cobb Accessport, EcuTek, OpenSource), the factory radiator becomes the bottleneck on hot days and at the track. The KOYORAD upgrade restores proper cooling headroom and lets the tune deliver its full power consistently.

Stage 3 — Built motor, big turbo, serious power. At this point the KOYORAD is non-negotiable, and you should also be looking at supporting fuel system upgrades and possibly an external oil cooler for genuinely demanding use.

Supporting Mods for the Subaru WRX/STI

The radiator handles cooling — for the rest of the Subaru build, pair with the Chicane Australia Subaru range:

• Brakes: DIXCEL brake pads for street and track WRX/STI use
• Suspension: Hardrace control arms, bushings and supporting suspension components
• Exhaust: KORSH catbacks and downpipes
• Fuel system: Injector Dynamics injectors for E85 and big-power builds

Shop the Full KOYORAD Range

KOYORAD main collection
KOYORAD for Nissan Skyline R32 / R33 / R34
KOYORAD for Toyota 86 / Subaru BRZ / GR86

Need help choosing the right KOYORAD for your Subaru? Contact us or email sales@chicaneaustralia.com.au — we know the EJ and FA platforms and we'll spec the right radiator for your build.