Parts for your 2018 Nissan Serena-Radiator cap

2018 Nissan Serena radiator-cap: what’s actually fitted and why it matters

Looking for a radiator cap for a 2018 Nissan Serena? Here’s the straight answer. Referencing Nissan’s C27 Serena Service Manual (CO – Cooling System) and the 2018 Owner’s Manual maintenance guidance, the radiator itself does not use a traditional filler neck with a cap. Instead, the cooling system is a sealed design with a remote, pressurised reservoir cap. On S-HYBRID (MR20DD) models there’s a single engine-coolant reservoir with a pressure cap, on e-POWER variants there are separate reservoirs (engine/generator loop and motor/inverter loop), each capped, but still no cap on the radiator core.

That’s why a “radiator cap” listing isn’t relevant to the Serena’s radiator neck—there isn’t one. The pressure cap lives on the reservoir(s), performing the same job as the old-school radiator cap: setting system pressure, raising the coolant’s boiling point, and allowing expansion and recovery as temperatures swing. Nissan moved to this layout for safer access, better packaging under the bonnet, improved deaeration, and to reduce leak points that come with a filler neck on the radiator.

Owners chasing a replacement should be looking for the reservoir pressure cap that matches their variant. Most C27 caps are rated around 0.9 bar (approx. 88–90 kPa), stick with an OEM-equivalent rating and a cap design specified for the Serena’s tank. If it’s an e-POWER Serena, check which loop you’re servicing, as each reservoir uses its own cap and coolant circuit.

• Why it’s done this way:
  • Safer top-up point away from hot radiator core
  • Simpler bleeding and air separation
  • Fewer joints and potential leak sites
  • Easier packaging for hybrid and e-POWER layouts
• When to replace the cap:
  • Coolant pushes past the cap into overflow or there’s unexplained loss
  • Hoses collapse on cool-down (vacuum valve may be sticking)
  • Rubber seal looks cracked, hardened, or distorted

Quick tip: only remove the reservoir cap when the engine is dead cold. Use Nissan Genuine Blue Long Life Coolant (or an equivalent meeting Nissan specs) and keep the mix correct. If the system won’t hold pressure after a cap swap, pressure-test the cooling system to rule out leaks elsewhere.

• Does a 2018 Nissan Serena have a radiator cap?
  Yes and no. There’s no cap on the radiator itself. The pressure cap is fitted to the coolant reservoir (and e-POWER models have separate reservoirs/caps for the different loops). Functionally, it’s the same job as a traditional radiator cap—just mounted remotely.
• Which cap pressure rating should be used?
  Most 2018 Serena variants specify a cap around 0.9 bar (about 88–90 kPa). Always match the rating and design to the vehicle’s build and engine type. If in doubt, confirm by VIN against Nissan parts data or the under-bonnet label.
• How often should the cap be replaced?
  There’s no fixed interval, but it should be inspected at every coolant service. Replace it if the seal is tired, the spring is weak, or if pressure testing shows it won’t hold the specified rating. Many workshops pre-emptively replace caps around major coolant change intervals to avoid nuisance overheating.