Parts for your 2013 Mazda Cx-9-Radiator cap

2013 Mazda CX-9 radiator cap — what’s actually fitted?

Based on Mazda’s own Workshop Manual for the 2013 CX-9 (Cooling System section) and the Mazda electronic parts catalogue for this model year, there isn’t a traditional radiator cap on the radiator itself. Instead, this CX-9 uses a sealed radiator and a remote, pressurised coolant reserve/surge tank. The pressure cap lives on that tank and does the job most people think of as the “radiator cap”. So, a radiator-mounted cap isn’t relevant on this vehicle — the system is filled and pressure-managed via the tank cap under the bonnet.

Why do Mazda and plenty of other manufacturers do this? A remote, pressurised surge tank sits at the highest point of the cooling system, which helps purge air, keeps pressure stable, and makes bleeding and topping up cleaner and safer. It also means the radiator stays sealed, reducing potential leak points and improving long-term reliability. Mazda’s technical literature calls the part a “coolant reserve tank cap (with pressure valve)”, which confirms the cap’s function is integrated with the reservoir rather than the radiator.

Servicing-wise, even though there’s no cap on the radiator, the cap on the coolant tank is the service item to keep an eye on. It holds system pressure (typically around 1.1 bar/16 psi for this platform — always match the rating shown on the cap or in the owner’s manual) and manages expansion and return flow as the engine heats and cools. If the spring weakens or the seals harden, you can see slow coolant loss, overheating under load, or hoses that collapse as the engine cools.

• Check the cap during regular servicing: look for cracked rubber, crusty deposits, or a sticky valve.
• Only remove the cap when the engine is stone-cold. Cover with a rag and turn slowly to release any residual pressure.
• Replace the cap if in doubt — it’s inexpensive and protects far pricier components.
• Use the correct long-life coolant (Mazda FL22 or equivalent) and follow the bleed procedure to avoid trapped air.

Popular questions about 2013 Mazda CX-9 radiator caps

Where is the radiator cap on a 2013 Mazda CX-9?
It’s on the pressurised coolant reserve/surge tank, not on the radiator. Lift the bonnet and you’ll see the plastic tank with a labelled pressure cap — that’s the one to use for checks and fills.

What pressure rating cap does the 2013 CX-9 use?
Most 2013 CX-9s use a cap around 1.1 bar (about 16 psi). Always match what’s printed on your existing cap or the spec listed in your owner’s manual or Mazda service information.

How can someone tell if their CX-9’s cap needs replacing?
Signs include coolant weeping around the cap, overheating in traffic or on climbs, a sweet coolant smell, collapsed top hose after cool-down, or a low coolant level despite no obvious leaks. If any of these show up, test or replace the cap.