CSF FL5 Type R vs FE1 Civic Si Radiator: Which Fits Your Build?

Quick answer

For an FL5 Civic Type R or DE5 Integra Type S, choose the CSF FL5 radiator for its 2-row 42mm core and CNC-machined brackets. For an FE1 Civic Si or DE4 Integra, the CSF FE1 radiator is the direct fit and costs less.

Why the FL5 radiator costs more than the FE1

The price gap reflects the hardware, not a difference in brand. The FL5 unit uses a 2-row, 42mm ultra-high-performance core with B-Tube technology, 5mm multi-louvered fins, CNC-machined mounting brackets, and a hand-polished finish. The FE1 unit is also a full aluminum radiator, but its catalog listing does not itemize core thickness or bracket construction, so you are paying for a simpler direct-fit upgrade rather than the FL5's larger core and machined mounts.

That matters if you track the car or live in a hot climate: the FL5 radiator's extra core volume and surface area are aimed at sustained heat, while the FE1 radiator is sized for the Si's lower-output engine and typical street or light-track use.

Chassis fit is not interchangeable

These radiators are listed for different platforms. The FL5 radiator is specified for the 2023+ FL5 Civic Type R and 2024+ DE5 Integra Type S. The FE1 radiator is specified for the 2022+ FE1 Civic Si and its DE4 Integra sister car. The catalog does not list a shared fitment, so do not assume one will drop into the other chassis.

If you are unsure which platform you have, check the model year and trim on your registration before ordering. Buying the wrong radiator means return shipping and downtime.

What the FL5 coolant temperature benefit depends on

A larger core helps only when the rest of the cooling system can use it. If your FL5 still runs the stock thermostat, fan settings, and coolant mix, the CSF radiator can lower peak temperatures on track, but it will not fix a tuning or airflow problem. The catalog does not supply before-and-after temperature data, so treat any claimed drop as dependent on your setup, ambient temperature, and driving style.

For street driving, the FL5 radiator is mostly insurance. For repeated hot laps, it is the more appropriate choice because the 42mm core and louvered fins are designed to reject heat over longer periods.

Trade-offs to weigh before you buy

• Cooling headroom vs cost: The FL5 radiator's 42mm core offers more heat rejection than the FE1 unit, but it costs more and is only listed for the FL5/DE5 platform. If you track regularly or see high coolant temps, the FL5 core is the safer choice; for a street Si, the FE1 radiator covers the need at a lower price.
• Plug-and-play vs platform lock: Both are described as plug-and-play for their listed chassis, but neither catalog listing shows cross-platform fitment. Confirm your chassis code before ordering; a plug-and-play radiator for the wrong platform is not plug-and-play.
• Finish and hardware: The FL5 radiator includes CNC-machined mounting brackets and a hand-polished finish; the FE1 listing does not itemize those details. If you want a show-quality engine bay or precise bracket fit, the FL5 unit's hardware is the differentiator.

Product facts

• 2022+ CSF FL5 Civic Type R High-Performance Radiator: 2-row, 42mm ultra-high-performance core with B-Tube technology and 5mm multi-louvered fins. The thicker core and fin design add heat capacity for track sessions and hot-climate driving.

  

• 2022+ CSF FE1 Civic Si High-Performance Radiator: Listed for the 2022+ FE1 Civic Si and DE4 Integra with a direct-fit design. It is the simpler, lower-cost cooling upgrade for the Si platform without the FL5's larger core.

  

Which radiator fits your build?

Best for

• 2023+ FL5 Civic Type R or 2024+ DE5 Integra Type S owners who track the car or drive in hot climates
• Builds that want CNC-machined brackets and a polished finish

Not for

• FE1 Civic Si or DE4 Integra owners, because the FL5 radiator is not listed for those chassis
• Budget-focused street builds that do not need the extra core volume