Parts for your 2000 Holden Commodore-Radiator cap

2000 Holden Commodore radiator cap: where it is, what it does, and when to replace it

Based on technical references — including the Holden VT/VX Series Service Manual (Cooling System section), the 2000 Commodore Owner’s Handbook filling procedure, and common parts catalogues from major suppliers — the 2000 Holden Commodore uses a pressurised cooling system with the pressure cap fitted to the plastic surge/expansion tank, not on the radiator neck itself. So a radiator cap absolutely is relevant to this model, it’s simply located on the coolant reservoir that sits beside the radiator.

On a 2000 Commodore (VT Series II or early VX), the radiator cap’s job is to hold system pressure to a specific rating, typically around 110–120 kPa (check the vehicle’s label or the old cap). By sealing the system and controlling pressure, the cap raises the coolant’s boiling point, helping the engine run at the right temperature in Aussie and Kiwi conditions — from slow traffic on a scorching day to long open-road climbs. The cap also has a vacuum relief valve. When the engine cools and coolant contracts, that valve allows coolant to be drawn back from the tank so hoses don’t collapse and air doesn’t sneak in.

As part of routine servicing, the radiator cap on the surge tank deserves a quick test and inspection. A weak spring, flattened or cracked seals, or a sticky valve can cause hard-to-trace issues like gradual coolant loss, a whiff of coolant after shut-down, random temp spikes on hills, stains or crust around the tank neck, or hoses that collapse when cold. A workshop can pressure-test the cap in a minute, if it doesn’t hold the specified pressure or release/return correctly, replace it.

• Only remove the cap when the engine is stone cold. If it’s warm, use a rag and crack it slowly to vent pressure.
• Match the cap’s pressure rating to the vehicle/engine spec, don’t guess or “upgrade” the pressure.
• Inspect the surge tank neck for cracks or roughness. Clean the seat and lightly moisten the seal with fresh coolant before fitting.
• Hand-tighten until fully seated, no tools needed.
• Good practice is to test the cap at each coolant service and replace it every few years, or immediately if it fails a test.

Whether it’s a V6 or V8, keeping a healthy, correctly rated cap on the Commodore’s surge tank helps protect the water pump, radiator, heater core and hoses, and keeps the temp gauge nice and boring — exactly how it should be.

Popular questions about 2000 Holden Commodore radiator caps

Where is the radiator cap on a 2000 Commodore?
It’s on the pressurised plastic surge/expansion tank beside the radiator, not on the radiator itself. Look for the round cap on the coolant reservoir under the bonnet.

What pressure rating cap does it need?
Most 2000 Commodores use a cap in the 110–120 kPa range. Check the existing cap, under‑bonnet label, or a trusted parts guide for the exact spec for your engine variant.

How often should the cap be replaced or tested?
Have it pressure-tested whenever the cooling system is serviced, and replace it if it fails, shows perished seals, or every few years as preventative maintenance.