Parts for your 2004 Honda Elysion-Radiator cap

2004 Honda Elysion radiator cap — what it does and when to replace it

Yes, the 2004 Honda Elysion (RR1–RR5, K24A 2.4 and J30A 3.0) is built with a conventional radiator cap on the radiator’s upper tank. Technical sources: Honda Elysion Service Manual (Cooling System, Radiator Cap Inspection) specifies a 1.1 bar/108 kPa cap and outlines test/replacement, and the Honda Japan EPC lists “Cap, Radiator (1.1)” p/n 19045-PAA-A01 for the Elysion cooling system. So a radiator cap is absolutely relevant on this model.

The radiator cap on a 2004 Elysion quietly does heaps of work. It seals and pressurises the cooling system to about 1.1 bar, which raises the coolant’s boiling point so it can carry more heat without boiling over. Inside are two little valves: a pressure valve that lets excess pressure vent to the overflow bottle when things get hot, and a vacuum valve that pulls coolant back in as the engine cools. That back-and-forth keeps the system full, air-free, and happy.

Because the cap is a wear part, it’s worth giving it attention during routine servicing. A tired cap can cause annoying issues like slow overheating at highway speed, coolant mysteriously ending up in the overflow bottle, or even a top hose that collapses after shutdown because the vacuum valve sticks. On the Elysion, a cap pressure of 1.1 bar is the go, stick with the Honda-style neck (often referred to as Type F) and use a quality genuine or equivalent unit.

• Good times to replace the cap: after any overheat, if there’s crusty staining around the neck, if the rubber seal is hard/cracked, or every 4–5 years/80–100,000 km as cheap insurance.
• Basic checks: with the engine stone-cold, pop the cap off and look for nicks on the rubber, bent tangs, or corrosion on the neck. A workshop can pressure-test the cap to confirm it holds spec (around 108 kPa).
• Safety tip: never open the cap hot. Wrap a rag around it and crack it slowly once it’s fully cool.

When fitting a new cap, clean the filler neck so the seal beds nicely. If you’ve drained coolant, bleed the system properly: fill slowly, run the heater, bring it up to temperature, and top up the overflow bottle to the MAX line. For Elysion V6s that work hard or tow, staying on top of the cap and coolant is a smart move to keep temps steady under the bonnet.

Popular questions

What pressure radiator cap does a 2004 Honda Elysion use?
Honda specifies a 1.1 bar (approximately 108 kPa) cap for the Elysion. That rating keeps the boiling point up without over-stressing hoses and seals. Matching the correct rating matters for stable temps and coolant recovery.

Where is the radiator cap on the Elysion?
It’s on the top tank of the radiator, under the front bonnet, near the upper support panel. There’s also a separate overflow bottle nearby, that bottle’s cap isn’t pressurised—the real pressure control is at the radiator cap.

How often should the cap be replaced?
Inspect it at every service. If it’s original or older than about 4–5 years, swapping it pre-emptively is inexpensive protection. Replace immediately if a pressure test fails, after any overheat, or if there are signs of leakage or a collapsed upper hose after cool-down.