Parts for your 2019 Toyota Mark x-Radiator cap

2019 Toyota Mark X radiator cap — what it does and how to look after it

Technical sources including Toyota’s Electronic Parts Catalogue for the GRX130/135 series and the Toyota Repair Manual cooling system section confirm that the 2019 Toyota Mark X is fitted with a pressure radiator cap mounted on the radiator’s top tank. The part is listed as a Cap Sub‑Assy, Radiator, commonly a 1.1 bar (approx. 108 kPa) cap used to regulate system pressure.

On the 2019 Mark X, the radiator cap is a small but vital bit of kit. It seals the cooling system, holds the correct pressure, and controls coolant flow between the radiator and the overflow bottle as temperatures change. By maintaining around 1.1 bar, it lifts the coolant’s boiling point, helping the V6 stay cool under the bonnet on hot Aussie and Kiwi days, long motorway runs, or twisty back roads. When pressure goes a touch high, the cap’s valve vents coolant to the reservoir, as things cool down, it draws coolant back in so the system stays topped and tidy.

As part of servicing, the cap deserves a quick once‑over. A perished rubber seal, sticky spring, or a weak pressure valve can cause hard‑to-trace overheating, low heater output, or that tell‑tale sweet smell of coolant. It’s smart practice to replace the radiator cap every 80,000–100,000 km or 4–5 years, or sooner if there’s any doubt. Always match the pressure rating stamped on the cap (typically 1.1) and stick with a genuine or reputable brand — the wrong rating can stress hoses, trigger leaks, or lower the boiling point and invite overheating.

Safety first: never pop the cap when hot. Let the car cool completely, then use a rag and twist slowly to the first detent to bleed any residual pressure before removing. While there, check for crusty deposits, nicks in the seal, or a rough seating surface on the filler neck. If a shop has a pressure tester, they can bench‑test the cap to confirm it holds its rated pressure. Pair a fresh cap with Toyota Super Long Life Coolant (pink) at the correct mixture and, after refilling, run the heater, squeeze the upper hose to help burp air, and top up the overflow to the “FULL” mark.

A couple of quick watch‑fors:

• Random temp swings, hoses going rock‑hard, or coolant staining near the neck can point to a tired cap.
• The reservoir cap is not a pressure cap — the pressure job is handled at the radiator.

FAQs

Does the 2019 Toyota Mark X have a radiator cap and where is it located?

Yes. The 2019 Mark X (GRX130/135) uses a pressure radiator cap on the radiator’s top tank. Pop the bonnet and look at the upper corner of the radiator, the bayonet‑style cap sits on the filler neck, while the nearby plastic bottle is the overflow reservoir with a non‑pressurised lid.

What pressure rating should the Mark X radiator cap be?

The factory spec is typically 1.1 bar (about 108 kPa). Use a cap with the same rating stamped on the top. A lower rating can promote boil‑over, a higher rating can stress hoses, joints, and the radiator.

How often should the radiator cap be replaced?

As a rule of thumb, every 80,000–100,000 km or 4–5 years, or sooner if seals are cracked, the spring feels weak, or there are signs of leakage. It’s a low‑cost part that can prevent bigger cooling headaches.