Parts for your 2016 Toyota Mark x-Radiator cap

2016 Toyota Mark X radiator cap — what it does and how to look after it

Technical sources confirm the 2016 Toyota Mark X (GRX130/GRX133) is fitted with a radiator pressure cap. Toyota’s Electronic Parts Catalog (EPC) lists a Cap Sub‑Assy, Radiator for these models (commonly 16401‑31650, rated 108 kPa/1.1 bar), and the Toyota Mark X workshop/repair manual includes radiator cap pressure testing and replacement in the Cooling System section. So a radiator cap is absolutely relevant on this vehicle.

On the 2016 Toyota Mark X, the radiator cap does much more than just seal the filler neck. It regulates cooling system pressure so the coolant’s boiling point rises, letting the engine run efficiently without boiling over on a hot day or a hard uphill pull. The spring-loaded pressure valve vents excess pressure to the overflow bottle when things heat up, while the vacuum valve pulls coolant back in as everything cools and contracts. That push–pull keeps the system full and air-free under the bonnet.

Because the cap is a small part doing a big job, it’s worth giving it a bit of love during servicing. A crook cap can cause hard-to-pinpoint dramas — intermittent overheating at highway speeds, coolant loss with no obvious leaks, collapsed hoses after cool-down, or dried pink/white crust around the filler neck from Toyota Super Long Life Coolant (SLLC).

• Inspection cadence: check the cap at every service (about 10,000 km or 6 months).
• Pressure test: with a cap tester, it should hold close to its rating (typically 108 kPa/1.1 bar) and not bleed down quickly.
• Seal condition: look for nicks, hardening, or swelling of the rubber seals, and a smooth, clean seat in the radiator neck.
• Replacement timing: a good rule is to replace the cap whenever coolant is renewed (around 5 years/160,000 km for Toyota SLLC), or sooner if tests fail.
• Correct spec: match pressure rating and neck style, genuine or quality OEM-equivalent only.

Safety first: never pop the radiator cap when the engine’s hot — let it cool right down to avoid a scalding geyser of coolant. When fitting, ensure the cap is properly seated and turned fully to the stop. Keeping the 2016 Toyota Mark X radiator cap in top nick is cheap insurance for a healthy cooling system, stable temps, and long engine life.

Popular question 1: What pressure radiator cap does a 2016 Toyota Mark X use?

Most GRX130/GRX133 Mark X models use a 108 kPa (1.1 bar) cap. That rating is commonly stamped on the cap itself. If in doubt, check the vehicle’s cap or verify by VIN in the Toyota EPC to avoid under‑ or over‑pressurising the system.

Popular question 2: Where is the radiator cap on a 2016 Mark X?

It’s on the top tank of the radiator, near the upper hose connection when looking into the engine bay with the bonnet open. The translucent overflow bottle nearby is not pressurised — the pressure cap lives on the radiator neck.

Popular question 3: How often should the radiator cap be replaced on a 2016 Toyota Mark X?

Inspect every service and pressure-test periodically. Many owners replace the cap at coolant change intervals (about 5 years/160,000 km with Toyota SLLC), or straight away if seals are damaged or it can’t hold rated pressure.