Holden Commodore Overheating (VT–VZ)? Causes and Fixes (Australia)

Overheating is one of the most common complaints on the VT to VZ Holden Commodore, particularly the V6. The good news is that a lot of the causes are cooling-system parts an owner can check; the important news is that overheating is one problem you can't ignore, because a Commodore that keeps running hot can warp the cylinder head or blow a head gasket. The exact cause depends on your engine and year, so if you want it narrowed down quickly the app can help diagnose your specific vehicle — but this guide covers what's usually behind it and what to check. First, a safety point that matters more than anything else here.

If the gauge is in the red, stop

If the temperature gauge is climbing into the hot zone or you see steam, pull over safely and switch the engine off as soon as you can. Continuing to drive a seriously overheating engine is how a cheap fix becomes an engine rebuild. And never open the radiator cap or coolant expansion tank while the engine is hot — the system is pressurised and can spray scalding coolant. Let it cool right down first.

Common causes on the Commodore

Low coolant or a coolant leak

The most common starting point is simply not enough coolant, usually because it's leaking out somewhere. Look for green or orange residue, drips under the car, or a low expansion tank. On the Ecotec V6 in particular, a coolant leak from the plastic inlet manifold area is a well-known Commodore issue worth having checked if you're losing coolant with no obvious external puddle. Hoses, the radiator and the water pump are the other usual leak points.

Stuck thermostat

The thermostat opens to let coolant flow to the radiator once the engine warms up. If it sticks closed, coolant can't circulate properly and the engine overheats — often fairly quickly, and sometimes even in cool weather. A stuck thermostat is a common and relatively inexpensive cause worth ruling out early.

Blocked or failing radiator

Over years of service the radiator can clog internally or its plastic end-tanks can crack and leak — both common on older Commodores. A radiator that can't shed heat will let the engine run hot, especially when working hard or in traffic. Signs include leaks at the radiator, or overheating that's worse under load.

Water pump

The water pump circulates coolant through the engine. A worn or failing pump — leaking from its weep hole, or with a failing impeller — can't move coolant properly and leads to overheating. It's a mechanical part that wears with age and kilometres.

Cooling fan not running

The Commodore relies on electric cooling fans to pull air through the radiator at low speed. A classic clue: if it overheats in stop-start traffic but stays cooler on the open road, a fan that isn't kicking in is a prime suspect — the airflow from driving masks the problem until you slow down. The fault can be the fan, its relay, or a temperature sensor.

Head gasket (cause and consequence)

A failed head gasket can cause overheating — and repeated overheating can cause a failed head gasket, so the two are linked. Signs include coolant loss with no external leak, thick white smoke from the exhaust, a sweet smell, or a milky look under the oil cap. This one is serious and needs a mechanic.

Quick symptom guide

What you can safely check yourself

With the engine completely cool, you can rule out the simple causes and gather useful clues:

• Check the coolant level in the expansion tank — only ever with the engine cold, never hot.
• Look under the car and around the engine for coolant leaks, drips or dried residue.
• With the engine idling from cold and warming up, watch whether the cooling fan kicks in as it heats up.
• Look at the radiator for leaks, damage or crusty residue around the end-tanks.
• Note when it overheats — in traffic, under load, on the highway, or all the time — as it points at different causes.

The big safety rules with overheating: never remove the radiator cap or expansion tank cap while hot, don't keep driving a car that's in the red, and top up coolant only once the engine is cold. If you're not confident, it's fine to stop here and get it checked.

When to see a mechanic

Get professional help if the Commodore keeps overheating after you've checked the coolant and fan, if you're losing coolant with no obvious leak, or if there's white smoke, a sweet smell or milky oil — signs that point at a head gasket. Overheating damage compounds fast, so it's one of the cheaper problems to fix early and one of the most expensive to ignore.

Not sure why your Commodore is running hot? Once it's cool, note when it happens and whether you're losing coolant, then describe it — and get a diagnosis tailored to your exact model and engine.