Where Heat Comes From on the FL5

The FL5 doesn’t usually have issues cruising around town. Problems show up when you add sustained boost, track time, higher ambient temps, and full bolt-on or tuned setups.

Main heat sources:

Air-to-Air Intercoolers (A2A)

This is where most people start, and for many street + street/track builds it’s a great move. A stronger A2A helps delay heat soak and improves repeatability when you’re doing back-to-back pulls.

Pros

• Simple, proven, low maintenance
• No extra pumps, wiring, or coolant circuits
• Solid improvement over stock for many setups

Cons

• Still limited by front airflow
• Heat soak after repeated pulls / long sessions
• Very large cores can add pressure drop
• FL5 bumper space is tight

Brands worth looking at: PRL Motorsports, RV6 Performance, MDR, COBB, WOT Performance

Advice: If you’re mostly street, choose a proven core that fits cleanly and doesn’t kill airflow to the radiator. If you track the car, prioritize repeatability and airflow management over “biggest core possible.”

Radiators (Underrated but Important)

Radiators don’t get talked about enough, especially for track-driven FL5s. A better radiator doesn’t “add power” — it prevents your power from falling off when the session gets hot.

What a better radiator does:

• Helps stabilize coolant temps
• Reduces heat buildup during long sessions
• Takes stress off the entire cooling system

Brands to consider:

• PWR – race-proven quality (pricey; not required for most)
• WOT  – great quality and results. Comes with a Transmission Cooler that does not block flow to the Radiator. Great package deal.
• CSF – strong performance and great value

Airflow Control & Cooling Plates (Undertray / Cooling Tray)

Cooling isn’t only about bigger parts — it’s also about using the airflow you already have. Sealing and ducting can make your radiator and intercooler noticeably more effective, especially once temps climb on track.

Cooling plates / airflow control help:

• Seal gaps around the radiator/intercooler stack
• Prevent air from escaping instead of passing through cores
• Improve consistency (especially on track)
• Help manage airflow under the front end with a proper undertray setup

Note: WOT Performance is also great for airflow/ducting-focused solutions. Airflow control is one of the best “bang for buck” upgrades because it improves the performance of everything in the front stack.

Underhood Heat Management (Big Results)

Full bolt-ons generate more heat. Reducing radiant heat under the hood helps everything work better — intercooler efficiency, coolant stability, and overall consistency.

Supporting mods that actually help:

• High-flow downpipe with thermal coating (when possible)
• Turbo blanket and/or heat shielding
• Proper intake placement/shrouding (avoid pulling hot underhood air)

Coolant Options + Expansion Tanks

For most FL5 owners, OEM Honda coolant is already excellent and totally fine for street and light track use. If you’re seeing temps climb, the bigger issue is usually airflow + heat rejection (radiator/ducting), not the coolant itself.

Common coolant paths depending on goals:

Expansion tanks (quick note): These are mainly a durability/reliability upgrade (you already covered this in your dedicated blog), but they’re a solid “peace of mind” mod if you’re heat-cycling the car often.

New SBX Water-to-Air Intercoolers (W2A) (SBX Performance Prototype)

W2A is where things get really interesting for the FL5 — especially for track-focused builds or higher-power setups. Done correctly, W2A can deliver more consistent temps on repeat pulls and reduce pressure drop thanks to shorter charge routing.

• Shorter charge piping
• Less pressure drop
• Better consistency on repeated pulls
• Less dependent on front airflow conditions

W2A isn’t “better for everyone,” but for track/high-power consistency it can be a serious advantage when the system is engineered correctly. (We will be testing around city + highway driving to validate real-world behavior.)

Hidden Gem: AIRTEC Turbo Radiator (Turbo Coolant Cooler)

This is one of the most overlooked FL5 cooling upgrades — and one of the smartest. It targets heat at the source by cooling the turbo coolant circuit, reducing the heat feeding back into the system under boost.

Benefits:

• Lower turbo coolant temps
• Reduced overall coolant temperature
• Less ECU intervention under hard use
• Better lap-to-lap consistency

Oil Coolers (When You Actually Need One)

Oil cooling starts to matter when you’re doing regular track days, sustained high RPM driving, or higher boost setups. Oil temp control keeps the car happy for longer sessions and helps protect the engine under repeated heat cycles.

What to look for in an oil cooler setup:

• Thermostatic control for street/track balance (avoid overcooling)
• Proper airflow and mounting (don’t choke the main cooling stack)
• Quality lines/fittings for reliability

Gearbox Cooling (The FL5 Blind Spot)

The FL5 gearbox runs hotter than most people realize, especially on track. From the factory it uses a coolant-to-oil heat exchanger, which means heat can build up in both the transmission and the engine cooling system.

Why it’s a big deal:

• Cools the transmission oil directly
• Removes heat from the engine cooling system
• Increases total oil capacity
• Helps maintain temps for longer sessions

Putting It All Together: What Makes Sense

The “best” setup depends on how you drive. Prioritize consistency first, then add headroom where your temps show you need it.

Final Thoughts

Cooling mods don’t make your car flashy — but they make it faster for longer. The FL5 responds incredibly well to smart cooling upgrades, and choosing the right combination can mean more consistent power, better reliability, and less ECU torque reduction.