CSF 3781 Radiator

OE-Style Radiator for Honda Civic

CSF 3781 is an OE-style radiator built with an aluminum core and plastic tanks for direct replacement cooling performance. It is designed for 2016-2021 Honda Civic applications, including Honda Civic Si models, and uses a cross-flow layout with left-side inlet and right-side outlet connections.

Key Features

• Aluminum core with plastic tank construction
• Cross-flow radiator design
• Core thickness: 1 1/4 in.
• Single-row core configuration
• Inlet diameter: 1 1/4 left; outlet diameter: 1 1/4 right
• OE-style plastic tanks and aluminum core
• Cap not included

Detailed Description

CSF part number 3781 is engineered as a direct-fit radiator for 2016-2021 Honda Civic models, with fitment also listed for Honda Civic Si. The radiator uses a cross-flow layout and an OE-style plastic tank and aluminum core design to match factory-style cooling system architecture. With a 26 9/16 in. core length and 17 11/16 in. core width, this radiator is built around the dimensions needed for proper vehicle fitment and cooling system integration. CSF states its radiators are manufactured to high-performance standards and validated through wind tunnel testing for cooling performance.

This part cross-references Bosch 13582 and Spectra Premium CU13582 for the same application.

What This Radiator Helps Address

• Overheating caused by a leaking or restricted radiator
• Coolant loss from cracked plastic tanks or aged seams
• Reduced heat transfer from a worn or clogged core
• Temperature instability during daily driving or stop-and-go traffic
• Cooling system service needs on a 2016-2021 Honda Civic or Civic Si

Installation Notes and Tips

Verify inlet and outlet orientation before installation: inlet is left and outlet is right. Confirm all hose connections, mounting points, and surrounding cooling components match the OE-style layout before filling and bleeding the system. Because the cap is not included, reuse or replace the radiator cap as needed based on the vehicle’s cooling system requirements.

Quality Assurance

CSF manufactures radiators in ISO/TSO-certified facilities and supplies a broad range of radiator applications worldwide. Part number 3781 is built to OE-style specifications with aluminum core and plastic tank construction for consistent fitment on the listed Honda Civic applications.