Parts for your 2001 Holden Commodore-Radiator cap

2001 Holden Commodore radiator cap — what’s fitted and why it matters

For the 2001 Holden Commodore (VT Series II and VX), a radiator cap is indeed used — but it’s mounted on the pressurised coolant reservoir (header tank), not on the radiator neck. This layout is confirmed by the Holden/GMH VX Commodore Service Manual and common workshop references such as Gregory’s VT–VX manuals, which describe a sealed radiator with a remote pressurised cap on the expansion tank. So “radiator cap” remains a relevant service item on this model, even though it sits on the plastic tank rather than the radiator itself.

On these Commodores, the cap is a pressure-vacuum valve. Its job is to hold the cooling system at a specified pressure (typically around 110–120 kPa, as printed on the cap), which lifts the coolant’s boiling point and helps keep temperatures stable in Aussie and Kiwi conditions. When pressure gets too high, the cap vents to the reservoir to protect hoses, the heater core, and the radiator. As the engine cools, the cap also allows coolant to return, preventing hose collapse and helping the system self-bleed to a degree.

Because the cap is the system’s pressure gatekeeper, a tired seal or weak spring can cause hard-to-trace issues — hot-running in traffic, coolant loss, or random overflow bottle wetness. Regular visual checks are worth it: look for perished rubber on the cap, crusty deposits on the header tank neck, or hairline cracks in the bottle (a known ageing issue on VT–VX). Caps must only be opened stone cold.

• Service tip: inspect the cap at every service and replace it at the first sign of seepage, swollen or cracked seals, or if the pressure rating is illegible.
• Use an OE-quality cap with the correct pressure rating for the engine fitted (V6 or V8) and the proper thread/fitment for the Commodore header tank.
• After any cap replacement, check coolant level, run the engine to temperature with the heater on hot, and top up the reservoir as required following workshop bleed guidance.

Many workshops treat the cap as a low-cost “insurance” item whenever a cooling system is serviced — especially if the coolant bottle or radiator has been renewed. Replacing the cap every 3–5 years, or when doing major cooling work, helps avoid overheating dramas and premature hose or radiator failures. Sources: Holden/GMH VX Commodore Service Manual (Cooling System), Gregory’s VT–VX Commodore workshop manuals, and GMH technical service literature.

Where is the radiator cap on a 2001 Holden Commodore?

It’s on the pressurised coolant reservoir (header tank) in the engine bay, not on the radiator itself. The radiator is sealed, the reservoir cap is the system’s pressure cap and the main fill point when cold.

What pressure rating cap should a 2001 Commodore use?

Most VT–VX models use a cap around 110–120 kPa. The exact rating is printed on the cap and specified in workshop data. Using the wrong rating can lead to overheating or excess stress on hoses and the radiator.

How often should the cap be replaced?

Have it checked at every service and replace it at the first sign of leaks, damaged seals, or unclear markings. As a rule of thumb, many techs renew the cap every 3–5 years or during major cooling system work.