Parts for your 2022 Toyota Aqua-Radiator cap

2022 Toyota Aqua radiator-cap: used or not?

For the 2022 Toyota Aqua (second generation, MXPK11/MXPK16 with the M15A-FXE hybrid engine), the cooling system doesn’t use a traditional radiator cap on the radiator neck. Toyota’s service literature for this model, along with the Electronic Parts Catalogue for the MXPK series, shows a sealed, pressurised cooling system where the pressure cap sits on the coolant reservoir (degas/expansion bottle). The radiator itself is built without a filler neck, so there’s no separate “radiator-cap” to remove under the bonnet.

This design mirrors other late-model Toyota hybrids. The owner’s manual and workshop procedures specify filling and checking coolant only at the translucent reservoir, and they warn against opening the pressure cap when hot—clear signs that the cap’s function has moved from the radiator to the reservoir.

Why Toyota doesn’t use a radiator cap on the 2022 Aqua:

• Better air purging and cooling performance: With a pressurised degas bottle mounted at the system’s highest point, air is bled out more effectively, which helps prevent hot spots.
• Packaging and safety: Deleting a radiator filler neck supports lower bonnet lines and crash structures, and removes a scald-risk point at the front of the bay.
• Fewer leak paths and simpler checks: One cap, one seal, one level window—owners just check the reservoir’s COLD/FULL marks.

So while a “radiator-cap” isn’t fitted to the 2022 Aqua, the coolant reservoir pressure cap does the same job—holding pressure, managing boil-over, and allowing coolant to move between hot and cold states. During servicing, it’s worth inspecting that reservoir cap for a sound rubber seal, clean seating surfaces, and a spring that closes firmly. Replace it if the seal is cracked, the cap is sticky or hard to turn, or if there are symptoms like repeated coolant loss, gurgling after switch-off, or overheating. Always remove the cap only when the engine is stone-cold, and match the replacement to the original pressure rating shown on the cap. Use Toyota Super Long Life Coolant (pink) and top up only at the reservoir to the COLD FULL line—don’t mix coolant colours.

• Does the 2022 Toyota Aqua have a radiator cap?
  No. It uses a pressure cap on the coolant reservoir instead. The radiator itself has no filler neck.
• What cap should be replaced on a 2022 Aqua if there’s a cooling issue?
  The coolant reservoir (expansion tank) pressure cap. Choose a genuine or quality aftermarket cap that matches the original pressure spec printed on the cap.
• How should coolant be topped up on a 2022 Aqua?
  Only at the reservoir, when the engine is cold. Use Toyota Super Long Life Coolant (pink, premixed). If the level keeps dropping, have the system pressure-tested.