Parts for your 2002 Mazda 6-Radiator cap

2002 Mazda 6 radiator cap — does it actually have one?

According to Mazda’s own technical documentation for the first‑generation Mazda 6 (GG/GY, launched 2002) — notably the Workshop Manual Cooling System section and the Owner’s Manual maintenance guidance — this model doesn’t run a traditional cap on the radiator neck. Instead, it uses a sealed, pressurised expansion/degas tank with a screw-on pressure cap. The radiator itself has no filler neck. Coolant is filled and the system is pressurised via the reservoir cap, which performs the same job a “radiator cap” used to do on older layouts.

So, a conventional on-radiator cap isn’t used on the 2002 Mazda 6. The “radiator cap” people refer to for this car is actually the pressure cap on the coolant reservoir.

Why Mazda set it up this way:

• Better air separation: The high-mounted degas bottle lets trapped air migrate to the tank, helping bleeding and stable temperatures.
• Packaging and crash safety: No tall filler neck on the radiator, suiting the lower bonnet line and modern front-end design.
• Consistent system pressure: The reservoir cap manages pressure and vacuum recovery, pulling coolant back in as the engine cools.
• Simpler servicing: The manual specifies filling and checking at one point — the reservoir — reducing the chance of air pockets.

For anyone servicing a 2002 Mazda 6, treat the reservoir’s pressure cap as the critical piece. If the cap’s seal is cracked, the spring feels weak, or the cap won’t hold pressure, expect issues like coolant loss, overflow bottle burping, or running hotter than it should. Only remove the cap when the engine is stone cold. If replacing it, match the pressure rating stamped on the original cap (commonly around 1.1 bar/108 kPa for this platform) and use quality coolant that meets Mazda’s spec. A quick visual check of the cap and tank during each service — looking for perished rubber, white crusty deposits, or tank hairline cracks — goes a long way to keeping the cooling system sweet as.

• Where is the radiator cap on a 2002 Mazda 6?
  There isn’t one on the radiator. The pressure cap is on the coolant reservoir (degas bottle), that’s the functional “radiator cap” for this car.
• What pressure rating cap should be used?
  Typically around 1.1 bar (about 108 kPa). Always confirm the rating printed on the existing cap or under‑bonnet labels and match it.
• How can someone tell if the cap needs replacing?
  Look for a cracked or flattened rubber seal, weak spring tension, staining around the cap/tank, repeated coolant overflow, or slow warm‑up with poor heater performance. If in doubt, swap it — caps are inexpensive and can prevent bigger dramas.