Parts for your 2002 Nissan Primera-Radiator cap

2002 Nissan Primera radiator cap — what it does and when to replace it

Yes, the 2002 Nissan Primera (P12) uses a pressurised radiator cap. This isn’t a decorative bit under the bonnet — it’s a critical cooling-system component. Technical sources including the Nissan Primera P12 Service Manual (Section CO — Cooling System) and the Nissan Electronic Parts Catalogue (EPC) for 2002 list a radiator cap mounted on the radiator neck, typically a 0.9 bar (13 psi) cap, with genuine part numbers such as 21430-4M500 and 21430-7990A. Major aftermarket catalogues for Primera P12 back this up with the same pressure spec.

On the 2002 Primera, the radiator cap seals the system and controls pressure so coolant can run hotter without boiling, which keeps temps stable in Aussie and Kiwi conditions. It also has a vacuum valve that draws coolant back from the overflow bottle as the engine cools, preventing air pockets and collapsed hoses. When it’s doing its job, you get consistent cabin heat, steady temps, and fewer cooling dramas.

As part of routine servicing of a 2002‑nissan‑primera radiator-cap, it’s worth checking the cap every service and replacing it every 5–7 years or around 100,000 km, or sooner if there are issues. Always match the pressure rating (0.9 bar) and the correct neck depth/tab style for Nissan radiators. If in doubt, verify by VIN against the EPC or use a quality cap that meets JIS standards. A tired cap can cause slow overheating, mysterious coolant loss, hard or collapsed hoses, and crusty deposits around the neck.

• Common symptoms of a dodgy cap: coolant smell after shutdown, wet stains by the radiator neck, fluctuating temp gauge, weak cabin heater, or hoses that go flat after cooling.
• Safety tip: never crack the cap off when hot — wait until it’s cool, then open slowly with a rag.

When replacing the cap, wipe the sealing seat clean, lightly wet the rubber seal with fresh coolant, and ensure the overflow hose is clear. After fitting, top the radiator at the neck, set the overflow bottle to the MAX line, run the engine with the heater on hot, squeeze the upper hose to burp air, and recheck levels. It’s a small, low-cost part that can save the head gasket and keep the Primera happy on long runs.

• What pressure radiator cap does a 2002 Nissan Primera need?

The Primera P12 typically uses a 0.9 bar (13 psi) cap in the Nissan long‑reach style. Genuine references include 21430‑4M500 and 21430‑7990A. Always confirm by VIN or cap markings before purchase.

• Where is the radiator cap on the P12?

It’s on the radiator neck, usually at the top near the left side looking from the front. The overflow bottle cap isn’t pressurised — only the radiator cap seals and controls system pressure.

• Can a bad radiator cap cause overheating on a Primera?

Sure can. A weak cap lets coolant boil and vent early, then pulls air back in as it cools. That can cause temp spikes, low heater output, and even collapsed hoses. Replacing the cap often sorts these problems fast.