Parts for your 2020 Mazda Cx-5-Radiator cap

2020 Mazda CX-5 radiator cap — what’s actually fitted?

The 2020 Mazda CX-5 doesn’t run a traditional radiator-mounted cap. Mazda’s own technical documentation — the 2020 CX-5 Owner’s Manual (Maintenance and Care — Engine Coolant) and the CX-5 (KF) Workshop Manual — shows the pressurised cap lives on the coolant reservoir (also called the degas or expansion tank), while the radiator itself has no service-fill cap. So when people say “radiator cap” for this model, they’re really talking about the reservoir’s pressure cap.

Why the change? Modern cooling systems move the pressure cap to a remote, higher-mounted reservoir to improve reliability and serviceability. With the highest point of the system at the tank, air purges more easily, the engine bay packaging is cleaner, and there’s one safe, central place to check or top up coolant. Keeping the radiator sealed also reduces leak points and helps maintain stable operating pressure and temperature — all useful for efficiency and longevity.

For owners, that means the job is to look after the coolant reservoir pressure cap, not a radiator cap. It still does the same critical work: holding system pressure so the coolant’s boiling point stays high, and letting excess pressure vent to the tank when needed. If the cap gets weak or its seals perish, the CX-5 can creep towards overheating, push coolant out, or draw air back in as it cools.

• Check under the bonnet when the engine is stone cold. Inspect the reservoir cap’s rubber seals for cracks, flattening, or coolant crust.
• Watch for tell-tales: rising temps on hills, sweet coolant smell, stains around the tank neck, hoses that collapse as the engine cools, or a low heater output.
• If in doubt, a shop can pressure-test the cap with an adaptor for the CX-5 reservoir neck.
• Replace the cap if there’s any seal damage, if it fails a pressure test, or after cooling-system repairs where reliability is critical. Use a genuine Mazda cap or a quality equivalent that matches the specified pressure rating for your engine.
• Only open the cap when the engine is completely cold. Top up with Mazda-approved long-life coolant and keep the level between the marks on the reservoir.

This setup is exactly how Mazda engineered the 2020 CX-5 to run: a sealed radiator and a pressurised reservoir cap doing the heavy lifting, as confirmed by Mazda’s Owner’s and Workshop Manuals.

Does the 2020 Mazda CX-5 actually have a radiator cap?

No. The radiator itself has no removable cap. The pressure cap is fitted to the coolant reservoir (degas tank). Parts listings may still call it a “radiator cap”, but on this model the functional cap you service is on the reservoir.

What are the signs the CX-5’s cap needs replacing?

Look for dried coolant around the reservoir neck, a sweet smell, fluctuating temperatures, or hoses that go oddly soft or collapse as the engine cools. A cap that won’t hold pressure can also allow air in, leading to poor heater performance. A quick pressure test can confirm it.

Which cap should be used on the 2020 CX-5?

Use a genuine Mazda reservoir pressure cap or a high-quality equivalent that matches Mazda’s specified pressure rating for the specific engine. If unsure, match by VIN to ensure correct fit and rating. Avoid mixing in generic caps that don’t seal or pressurise to spec.