Parts for your 2019 Honda Odyssey-Radiator cap

2019 Honda Odyssey radiator cap — what it does and when to replace it

Based on Honda’s technical literature, a radiator cap is indeed used on the 2019 Honda Odyssey. The Owner’s Manual (Cooling System section) warns against opening the radiator cap when hot, and the Honda Service Manual cooling system specifications list a cap relief pressure of about 108–137 kPa (roughly 1.1 bar). Honda’s parts catalogue also shows a dedicated “radiator cap (1.1)” for RL6 (2018–2020) Odyssey models. It isn’t on the top tank of the radiator, instead, it’s mounted on the engine-side filler neck near the upper radiator hose, with a separate translucent reserve tank nearby.

On this Odyssey, the radiator cap is a small part with a big job. It seals the cooling system and holds pressure so the coolant’s boiling point lifts, helping the J35 V6 run at the right temperature even on scorching summer drives or towing the family trailer. The spring-loaded valve in the cap also manages expansion and contraction: when the coolant heats and expands, excess pushes past the cap into the reserve tank, when it cools, the cap’s vacuum valve draws coolant back to keep the system full and air-free.

If the cap’s spring weakens or the seals perish, pressure drops and the boiling point falls — that can trigger overheating, coolant loss, or hard-to-trace temperature swings. It can also let air sneak into the system, which isn’t great for water pump longevity or heater performance. Common clues include a sweet coolant smell, crusty deposits around the filler neck, a reservoir that’s always low or always overfull, or hoses that feel unusually soft after a hot shut-down.

As part of routine servicing of the 2019-honda-odyssey radiator-cap, it’s smart to:

• Inspect the cap at each service for cracked rubber, rust, or staining.
• Pressure-test the cap to its rated 1.1 bar during coolant service.
• Replace the cap proactively if age is unknown, at the first sign of seal wear, or whenever the cooling system is opened for major work.

When replacing, stick to the correct 1.1 bar spec and a quality OEM-equivalent or genuine Honda cap. Always work stone-cold — never crack a hot system. After refilling with the proper Honda Type 2 premix, bleed air as per the service procedure and confirm that the reserve tank sits between MIN and MAX when cold. Given Australia and New Zealand’s varied climates, many workshops pair a new cap with coolant changes or around the five-to-seven-year/100,000–120,000 km mark, or sooner if testing fails. It’s inexpensive insurance for temperature stability and long engine life.

FAQs

Where is the radiator cap on a 2019 Honda Odyssey?
It’s on the engine-side filler neck, close to the upper radiator hose — not on the radiator itself. The translucent plastic bottle nearby is the reserve tank, its cap isn’t pressurised.

What pressure rating does the 2019 Odyssey radiator cap use?
Honda specifies roughly 108–137 kPa (about 1.1 bar). Using the correct rating helps maintain the designed boiling point and cooling performance.

How often should the radiator cap be replaced?
Have it inspected and pressure-tested at regular services and at each coolant change. Many techs replace the cap every 5–7 years or around 100,000–120,000 km, or immediately if it fails a pressure test or shows seal damage.