Koyo N-FLO Dual Pass Radiator – 1989–1994 Nissan 180SX / Silvia S13 | SR20DET | Manual Transmission | HH020252N

Koyo HH020252N N-FLO dual pass radiator for the 1989–1994 Nissan 180SX and Silvia S13 with SR20DET engine and manual transmission. All-aluminium construction, 36mm core thickness, bolt-in fitment using factory mounting points and hose connections. Made in Japan. 13.8 lbs. Ships fast across Canada and the US.

Dual Pass Design — How It Works and Why It Matters

A standard single-pass radiator routes coolant from one tank, across the core once, and into the opposite tank before returning to the engine. The Koyo N-FLO dual pass routes coolant across the core twice before exiting — using a divider plate in one of the tanks to split the core into two passes:

• Pass 1: Hot coolant enters the radiator and flows across the upper half of the core.
• Pass 2: Coolant is directed back across the lower half of the core before exiting to the engine.

The result is that coolant spends approximately twice as long in the radiator core for a given flow rate — extracting significantly more heat per pass. On a turbocharged SR20DET, where heat rejection requirements are higher than the OEM radiator was designed for, the dual pass configuration provides meaningful cooling improvement without requiring a physically larger radiator. The N-FLO fits within the factory S13 radiator bay dimensions — no cutting or modification required.

36mm Aluminium Core

The OEM S13 radiator uses a thinner core with lower coolant volume. The Koyo N-FLO’s 36mm all-aluminium core provides:

• Greater coolant volume: More fluid in the core at any given moment means greater thermal mass to absorb heat spikes during hard acceleration or braking.
• More fin surface area: The thicker core accommodates more cooling fins, increasing the total surface area available for convective heat rejection to airflow.
• Aluminium construction: All-aluminium brazed construction is lighter than OEM copper/brass radiators and provides equal or superior heat transfer coefficient. Aluminium is also resistant to the electrochemical corrosion that affects copper/brass radiators over time with modern coolant chemistry.

SR20DET Cooling Context

The turbocharged SR20DET generates substantially more heat than the KA24E or naturally aspirated SR20DE. The factory S13 radiator is adequate for stock SR20DET at moderate use but becomes marginal under:

• Sustained track driving — where engine load and ambient underbonnet temperature are both elevated
• Increased boost pressure — higher boost = higher combustion temperatures and more heat rejection required
• Hot climate driving — particularly relevant for Canadian summer track days where ambient temps compound cooling demand
• Drift use — repeated high-RPM runs with limited forward airflow through the radiator during sideways sections

The N-FLO’s dual pass design and 36mm core address these demands without requiring aftermarket shroud modifications or fan upgrades in most street and club track applications.

180SX vs Silvia S13 — Both Covered

The HH020252N fits both S13 body styles that were equipped with the SR20DET and manual transmission:

• Nissan 180SX (RPS13): Fastback/hatchback body, sold in Japan 1989–1998. North American grey market imports are most commonly the 1989–1994 early chassis years covered by this radiator. The 180SX used the SR20DET from launch.
• Nissan Silvia S13 (PS13): Coupe body style, sold in Japan. Shares the same engine bay, cooling system mounting, and radiator dimensions as the 180SX.

Both share identical radiator bay dimensions and mounting points — the HH020252N is a direct bolt-in for either body style with SR20DET and manual transmission.

Installation

Direct bolt-in replacement using factory mounting points, upper and lower hose connections, and factory fan shroud. Drain the factory coolant completely before removal. After installation, fill with a quality 50/50 premix or distilled water and concentrated coolant (OAT or HOAT formula compatible with aluminium), and bleed the cooling system to purge air pockets before returning to normal driving. Check for leaks at all hose connections after the first heat cycle.

SR20DET manual transmission only — not for AT or KA24E. 1989–1994 S13 180SX and Silvia. 36mm dual pass aluminium core. Bolt-in fit. Made in Japan by Koyo.

Specifications

• Brand: Koyo
• Part Number: HH020252N
• Type: N-FLO dual pass radiator
• Core thickness: 36mm
• Construction: All-aluminium brazed
• Application: 1989–1994 Nissan 180SX / Silvia S13 — SR20DET — manual transmission
• Transmission compatibility: Manual only (MT)
• Origin: Made in Japan
• Weight: 13.8 lbs