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MOTRS

Commodore (VN-VZ) / HSV

1988-2006 / Sedan / Estate / Australia

All Commodore (VN-VZ) / HSV problems All workshop problems
Common Cooling System

Coolant Bleeding Issues (V6)

Symptoms

After any coolant work (thermostat, water pump, hose replacement, flush), the engine overheats intermittently or the temperature gauge fluctuates wildly. Heater blows hot then cold.

Cause

The Ecotec V6 cooling system has high points that trap air pockets. Air in the system prevents proper coolant circulation, causing localised hot spots. This catches many home mechanics out after routine coolant work.

Fix

Use a coolant bleed funnel (also called a spill-free funnel) attached to the radiator cap opening.

Fill the system with the funnel in place, start the engine, and run it until the thermostat opens.

Open the bleed screw on the thermostat housing to release trapped air.

The bleed funnel keeps the coolant level above the highest point in the system, allowing air bubbles to escape through the funnel rather than recirculating.

This is the method used by Holden dealerships and is far more reliable than the traditional fill-and-bleed approach.

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Other known issues

Common Cooling System

Thermostat Failure (All Models)

Engine runs cold (temperature gauge barely rises from the bottom), or overheats suddenly. Heater blows cold air despite the engine running. Fuel economy worsens because the engine never reaches operating temperature.
Critical Cooling System

Water Pump Failure (Ecotec V6)

Coolant leak from the front of the engine, below the water pump pulley. Whining or grinding noise from the water pump area. Overheating if the pump bearing seizes or the impeller fails.
Common Engine, V6 (Buick/Ecotec 3.8L, VN-VY)

Intake Manifold Gasket Leak

Coolant leak at the junction of the intake manifold and cylinder heads. May present as coolant loss without a visible external leak (coolant enters the intake ports), or as a coolant stain on the side of the engine. Engine may run rough or misfire if coolant enters the combustion chamber.
Critical Engine, V6 (Buick/Ecotec 3.8L, VN-VY)

Harmonic Balancer Failure (Ecotec, VS onwards)

A wobbling pulley on the front of the crankshaft. Knocking or rattling noise from the front of the engine. The drive belt may track poorly or come off.
Common Engine, V6 (Buick/Ecotec 3.8L, VN-VY)

Supercharger Bypass Valve Failure (L67 supercharged V6)

Loss of boost, rattling from the supercharger, reduced performance. The supercharger may make a whining noise that changes with the valve's operation.
Critical Engine, V6 (Alloytec 3.6L, VZ)

Timing Chain and Guide Failure

Rattling noise on cold start that may persist after warm-up. Check engine light with codes related to camshaft timing. Rough idle, misfiring, loss of power. In severe cases, the engine won't start or runs extremely poorly.
All Commodore (VN-VZ) / HSV problems