Parts for your 2012 Mazda Premacy-Radiator cap

2012 Mazda Premacy radiator cap — is it actually used on the radiator?

Short answer: not on the radiator itself. The 2012 Mazda Premacy (Mazda 5, CW series) uses a sealed radiator with a remote, pressurised coolant reserve tank (often called a degas or expansion bottle). The pressure cap lives on that tank, not on the radiator neck. This arrangement is shown in Mazda’s factory Workshop Manual for the CW series (Cooling System section) and in the Mazda electronic parts catalogue, which list a coolant reserve tank cap and a capless radiator.

Why Mazda set it up this way comes down to reliability, packaging, and easier bleeding. With the highest point of the system being the reserve tank, air purges more effectively, the system maintains stable pressure, and there’s less risk of someone popping a hot radiator cap under the bonnet. It also makes filling and checking coolant simpler—everything happens at the translucent tank, where the pressure cap and level markings are easy to reach.

So, for anyone searching “radiator cap” for a 2012 Premacy, the part that matters is the pressure cap on the coolant reserve tank. If that cap gets tired—weak spring, cracked rubber seal, or can’t hold pressure—coolant can boil earlier, overflow, or the heater can misbehave. A quick cap pressure test is a smart move during servicing. When replacing, match the factory pressure rating stamped on the original cap (commonly around 1.1 bar/16 psi on Mazda CW models) and choose a quality brand that’s compatible with Mazda’s FL22 long‑life coolant.

• Check the cap at service time for split seals, corrosion, or sticky movement.
• Pressure‑test the cap and cooling system if there are overflow or overheating symptoms.
• Replace the cap if it fails testing, shows damage, or is past its service life, it’s a low‑cost preventative fix.
• Always open the cap only when the engine is cold, and top up at the reserve tank using the correct FL22‑spec coolant mix.

With the right cap on the reserve tank and fresh FL22 coolant at the correct level, the Premacy’s cooling system stays happy across Aussie and Kiwi conditions—from weekday commutes to long summer road trips.

• Does a 2012 Mazda Premacy have a radiator cap?
  It doesn’t have a cap on the radiator neck. The pressure cap is fitted to the coolant reserve (expansion) tank, which controls system pressure and allows safe filling and bleeding.
• Where should the cap be checked or replaced on a 2012 Premacy?
  Under the bonnet at the coolant reserve tank. Inspect and replace that pressure cap if it’s worn, leaking, or fails a pressure test.
• What pressure rating cap does it use?
  Use a cap that matches the rating stamped on the original part for the CW‑series Premacy. Many Mazda CW models use a cap around 1.1 bar (16 psi), but always confirm against the existing cap or a Mazda parts lookup.