Parts for your 2008 Nissan Serena-Radiator cap

2008 Nissan Serena Radiator Cap — What It Does and When to Replace It

Technical documentation confirms the 2008 Nissan Serena (C25 series) does use a radiator cap. The Nissan Factory Service Manual for the C25 Cooling System (CO section) specifies a pressurised cap and provides a test spec of roughly 0.9 bar (about 88–108 kPa). Nissan’s electronic parts catalogue (FAST) also lists a radiator cap for C25 models. On most MR20DE petrol Serenas the cap sits on the radiator’s top tank under the bonnet, some diesel variants place the pressure cap on a pressurised reservoir instead. Either way, it’s the same job: seal, pressurise and manage coolant expansion.

A good radiator cap is small gear with a big job. It seals the cooling system and holds pressure so the coolant’s boiling point is raised, keeping temps steady in Aussie and Kiwi conditions. The spring-loaded valve in the cap also vents excess pressure into the overflow bottle as the engine heats up, then draws coolant back as it cools. If the cap gets tired, the Serena can run hot, blow coolant into the bottle, or suck air back in as it cools. That’s when hoses can collapse and the heater can go lukewarm.

As part of routine servicing, it’s worth checking the cap every 10,000–15,000 km or at each oil change. Only open it when the engine is stone cold. Look for perished rubber seals, a sticky or rusty spring, and a crusty neck on the radiator or reservoir. If the cap doesn’t hold the rated pressure on a tester, replace it. Match the rating printed on the original (commonly 0.9 bar on Serena petrol models, some diesels may differ). Sticking a random cap on because it “fits” can upset system pressures and cause dramas.

• Swap the cap proactively every 4–5 years or 80,000–100,000 km, especially if the Serena tows or sees hot summers.
• Use a quality, correct-pressure cap and make sure the overflow hose is clear and tight.
• Top up with Nissan-approved coolant mixture after cap replacement and bleed air as per the FSM procedure.

Tell-tale signs of a crook cap include frequent top-ups, coolant puking into the bottle, gurgling after shutdown, collapsed upper hose when cold, or overheating under load. Keeping this little part in shape helps the Serena’s MR20DE or diesel stay cool, comfy and reliable on the school run or the long haul.

Popular questions about the 2008 Nissan Serena radiator cap

Where is the radiator cap on a 2008 Nissan Serena?
On most MR20DE petrol models it’s on the top of the radiator, near the front under the bonnet. Some diesel variants use a pressurised reservoir with the cap on the plastic tank instead. The cap itself will show the pressure rating.

What pressure rating should the Serena’s cap be?
Nissan’s service literature for the C25 typically specifies around 0.9 bar (about 88–108 kPa). Always match what’s printed on the original cap or the vehicle label, as certain market/engine combos can vary.

How often should the radiator cap be replaced?
Inspect at every service and replace about every 4–5 years or 80,000–100,000 km, or immediately if it fails a pressure test, shows damaged seals, or there are symptoms like coolant loss or overheating.