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RX-8 · Reliability

RX-8 Radiator + cooling upgrade

Your RX-8

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Protects the engine
Medium$330–$6503–5 hrs
All RX-8 mods

Why do it

Rotary engines run hot and don't tolerate overheating well. A higher-capacity radiator adds a safety margin, especially in summer or on track days.

Tools you'll need

Parts to buy

Always double-check fitment for your exact year, trim and transmission before buying. Prices change. ModBuddy doesn't earn money from these links.

Before you start

  • The Mishimoto MMRAD-RX8-04 fits 2004–2008 manual cars. Automatic cars need a separate transmission cooler, and 2009–2011 cars need a different radiator.
  • Buy enough of the coolant type your service manual specifies (premixed is easiest).
  • The engine must be completely cold. Hot coolant can scald.

Video guide

RX-8 radiator install, step by step
by Driven By Madness on YouTube

The video uses a Koyo radiator with a different lower hose. The Mishimoto we list bolts into the stock mounts and uses the stock hoses, so skip his hose rerouting and pressure-test parts if you don't need them. Each ▶ button below jumps to that step in the video.

Watch the whole video

Steps

  1. Raise the front and remove the under-tray

    • Park on level ground, chock the rear wheels, and support the front on jack stands.
    • Remove the lower under-tray to reach the bottom of the radiator.
    • For more working room, many owners also remove the battery and its tray, and some take off the front bumper cover. The video clip for this step shows both.
    Watch this step (0:30–2:56)

  2. Drain the coolant

    • Put a large drain pan under the radiator and open the drain plug.
    • Coolant is toxic and tastes sweet to animals. Clean up spills right away and take old coolant to a recycling center.

  3. Disconnect the hoses and fans

    • Loosen the clamps and pull off the upper and lower radiator hoses. A twisting motion helps break them free.
    • Unplug the cooling fan connectors and free the wiring from any clips.

    Tip: The small plastic hose neck on the stock radiator (where the coolant tank hose connects) snaps very easily on older cars. Work that hose off gently, and have a replacement plan if it breaks.

    Watch this step (2:56–5:41)

  4. Remove the old radiator

    • Before you unbolt anything, zip-tie the A/C condenser's pipes to the car so the condenser stays put once the radiator is out. Snug, not tight.
    • Remove the radiator mounting bolts and nuts, then lower the radiator out the bottom of the car with the fan shroud attached. Go slowly so you don't damage the A/C condenser in front of it. Coolant will spill, so keep the drain pan under it.
    • Move the fans and shroud over to the new radiator if they're reused.
    Watch this step (5:41–7:20)

  5. Install the new radiator

    • Lower the new radiator into place, making sure it sits in its rubber mounts.
    • Reconnect both hoses with the clamps in their original positions, reconnect the fans, and install the supplied magnetic drain plug.
    Watch this step (7:20–9:45)

  6. Refill and bleed

    • The RX-8 radiator has no filler cap, so you fill through the coolant expansion tank.
    • Fill slowly, run the engine with the heater on high, and keep topping up as air bubbles out. Follow your service manual's bleeding procedure.

    Tip: Trapped air is the number-one cause of overheating after a radiator swap. Take your time bleeding, and recheck the level once the engine is cold again.

    Watch this step (9:45–11:53)

  7. Check for leaks

    • With the engine warm, check every hose connection and the drain plug for drips.
    • Reinstall the under-tray and lower the car.

How to know it worked

Safety first

  • Park on flat, solid ground, set the parking brake and chock the wheels.
  • Use jack stands rated for your car. Never get under a car held up only by a jack.
  • Let the engine and exhaust cool completely before touching them.
  • Disconnect the negative battery terminal before unplugging sensors or electrical parts.
  • Wear safety glasses, and gloves around sharp heat shields and hot fluids.
  • Tighten bolts to the torque spec in your factory service manual.
  • If a step doesn't match your car or you're unsure, stop and ask a shop.

These are overview steps written to help you plan the job. Always follow the instructions that come with your part and the procedures and torque specs in your factory service manual. Horsepower is an estimate; results vary.