Parts for your 2018 Mazda Cx-5-Radiator cap

2018 Mazda CX-5 radiator cap: does it have one, and what to know

Short answer: a traditional radiator cap on the radiator neck isn’t used on the 2018 Mazda CX-5 (KF series). Mazda’s factory documentation shows the pressure cap lives on the pressurised coolant reserve tank, not on the radiator itself. This layout is described in the Mazda CX-5 (KF) Workshop Manual under Cooling System component location and service procedures, echoed by the 2018 Owner’s Manual safety notes about only opening the “coolant reserve tank cap” when the engine is cool. Mazda’s electronic parts catalogue lists a pressure-rated “reserve tank cap” for the KF, and common aftermarket catalogues also specify a cap located on the expansion tank rather than the radiator.

Why no old-school radiator cap? The CX-5’s SKYACTIV cooling system uses a sealed, pressurised expansion tank as the highest point and primary fill location. Doing away with a radiator neck cap helps with:

• Packaging and crash safety under the bonnet
• Cleaner coolant deaeration and consistent self-bleeding
• Better pressure control and fewer leak points
• Reduced risk of scalding because the cap is remote and clearly labelled

What this means for servicing is simple: treat the coolant reserve tank cap as the radiator cap, because it does the same job—holding system pressure (typically about 108 kPa/1.1 bar) and allowing coolant to move between the system and the tank as temperatures change. During routine servicing, the cap should be inspected for a supple rubber seal, a clean seating surface, and a responsive spring. If a cooling-system pressure test shows the cap won’t hold its rated pressure—or if the seal is cracked or swollen—it’s time to replace it with a genuine Mazda unit or a quality equivalent of the correct rating.

Always open the cap only when the engine is cold. If the cap must be removed, a clean cloth over the cap and a slow half-turn to vent any residual pressure keeps things safe. Top-ups should use Mazda FL-22 long-life coolant (or equivalent premix) to the mark on the tank. Most workshops will check the cap at every service and often recommend replacement around the five-to-seven-year mark, or sooner if testing fails.

Common signs of a crook cap on a CX-5 include:

• Coolant loss with no obvious external leak
• Upper hose going flat after cool-down
• Overheating or gurgling sounds after shutdown
• Coolant stains around the tank neck

Popular questions

Where is the radiator cap on a 2018 Mazda CX-5?
It’s on the pressurised coolant reserve tank, not on the radiator. Pop the bonnet and look for the labelled cap on the plastic tank near the top of the engine bay. That cap is the pressure cap for the whole system.

What pressure cap does the 2018 CX-5 use?
Most 2018 CX-5 models use a cap around 108 kPa (about 1.1 bar). Using the correct rating matters for boiling protection and hose health, so it’s best to fit a genuine Mazda cap for the KF series or a high-quality equivalent with the same spec.

Can a standard radiator cap be fitted to the radiator itself?
No. The radiator isn’t designed with a filler neck on this model. The system is engineered around the sealed, pressurised expansion tank, so the only cap to service or replace is on that tank.