Question 1

Intake Manifold Gasket Leak

Accepted Answer

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. The intake manifold gasket on the 3.8L V6 is a composite material that deteriorates with heat cycling. Dex-Cool coolant (used by GM) has been implicated in accelerating gasket deterioration, though this is debated. The gasket sits between an aluminium intake manifold and iron cylinder heads, different thermal expansion rates stress the gasket. Replace the intake manifold gasket set. The job requires removing the intake manifold, fuel rail, and associated wiring. Parts: $80-150 for a quality gasket set (Felpro is the standard recommendation). Labour: 4-6 hours. This is one of the most common jobs on the 3.8L V6, and any competent home mechanic can tackle it with basic tools and a workshop manual. Retorque the intake manifold bolts to 20 Nm in the specified sequence, over-torquing warps the manifold and guarantees a future leak.

Question 2

Harmonic Balancer Failure (Ecotec, VS onwards)

Accepted Answer

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. The harmonic balancer (crank pulley) is a two-piece unit bonded with rubber. The rubber deteriorates with heat and age, allowing the outer ring to separate from the hub. The outer ring carries the serpentine belt and the crank position sensor reluctor, if it separates, the engine loses belt-driven accessories and may stall. Replace the harmonic balancer. The old one must be pulled with a balancer puller, do not pry it off or you'll damage the crankshaft nose. Torque the bolt to the specified value (200 Nm+). A new balancer is $100-250. The job takes 1-2 hours.

Question 3

Supercharger Bypass Valve Failure (L67 supercharged V6)

Accepted Answer

Loss of boost, rattling from the supercharger, reduced performance. The supercharger may make a whining noise that changes with the valve's operation. The bypass valve controls how much air recirculates through the supercharger at part throttle. The valve's internal diaphragm deteriorates, causing it to stick open (no boost) or closed (excessive boost at part throttle, which loads the engine unnecessarily). Replace the bypass valve actuator. Parts: $80-150 aftermarket. This is a 30-minute job. Some owners upgrade to a manual bypass valve for tuned applications.

Question 4

Timing Chain and Guide Failure

Accepted Answer

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. The Alloytec V6 uses plastic timing chain guides that become brittle with heat and age. As the guides deteriorate, the chain loses tension, stretches, and can skip teeth. The VZ Alloytec was the first application of this engine in the Commodore, and early units were more susceptible. Replace the timing chains (both banks), all guides, and tensioners. This requires removing the front cover, the engine may need to come forward or partially out of the bay depending on the workshop's preference. Parts: $300-500. Labour: 8-14 hours. Total cost at a workshop: $1,500-3,000. This is not a DIY job for most people.

Question 5

Oil Leaks from Timing Cover

Accepted Answer

Oil weeping or dripping from the front of the engine, behind the harmonic balancer area. The Alloytec timing cover uses a gasket and sealant that deteriorate with age. The cover itself can warp slightly from heat cycling. Reseal the timing cover. This is essentially the same job as the timing chain replacement, so do both at the same time. If you're replacing timing chains, there's zero additional cost to reseal the cover while it's off.

Question 6

Hydraulic Lifter Noise

Accepted Answer

Ticking or tapping noise from the top of the engine, worst on cold start. May persist for several minutes or be constant. The 304 V8 uses hydraulic lifters that collapse when worn. Infrequent oil changes and poor oil quality accelerate lifter wear. The lifter bores in the block can also develop wear, which allows the lifter to rock slightly and lose oil pressure. Replace the lifters. On the 304, this requires removing the intake manifold, rocker covers, and rocker assemblies. Parts: $150-300 for a complete set. Labour: 6-8 hours. If the lifter bores are worn, oversized lifters or bore repair is needed.

Question 7

Oil Pump Drive Shaft Failure

Accepted Answer

Sudden loss of oil pressure. Oil pressure warning light illuminates. Engine noise increases rapidly. Catastrophic engine failure if not caught immediately. The 304 V8's oil pump is driven by a shaft from the distributor (or a dedicated drive on EFI models). The shaft can develop a twist or break, stopping the oil pump entirely. Replace the oil pump drive shaft. This requires removing the distributor (where fitted) and extracting the shaft. Parts: $30-60. The bigger cost is the damage done before you noticed. If oil pressure drops, stop the engine immediately, do not drive the car to a workshop.

Question 8

Rear Main Seal Leak

Accepted Answer

Oil drips from the junction of the engine and gearbox. Oil may be visible on the underside of the bellhousing. The rear main seal on the 304 is a two-piece rope-type seal (early) or one-piece lip seal (later) that hardens with age. The one-piece seal is far more reliable. Many 304s have been retrofitted with the one-piece seal during rebuilds. Replace the rear main seal. This requires removing the gearbox or engine. Budget $500-1,000 for the job at a workshop. If the engine is out for other reasons, the seal itself is $20-40.

Question 9

Lifter Tick

Accepted Answer

Light ticking noise from the top of the engine, usually on cold start. May or may not persist once warm. The LS1 and LS2 use hydraulic roller lifters. The roller bearing in the lifter can develop a flat spot, causing a tick as it rotates on the camshaft lobe. Oil quality and change intervals directly affect lifter life. Some lifter tick is considered normal on LS engines, a light tick on cold start that disappears within 30 seconds is generally not a concern. If the tick persists after warm-up, replace the affected lifter(s). On the LS1/LS2, this requires removing the intake manifold, valve covers, and rocker arms. Replacing all 16 lifters while the engine is apart is sensible. Parts: $200-400 for a complete set. Labour: 6-8 hours.

Question 10

Valley Cover Oil Leak

Accepted Answer

Oil pools in the "valley" between the cylinder banks, visible when the intake manifold is removed. Oil may weep from the manifold area externally. The LS1/LS2 has a plastic valley cover (a plate that sits between the cylinder banks, under the intake manifold) with a rubber gasket that deteriorates with heat. The knock sensors sit under this cover, and oil leaking past the gasket can damage the knock sensor wiring harness. Replace the valley cover gasket. This requires removing the intake manifold. While it's apart, inspect and replace the knock sensor wiring harness if it's oil-soaked or brittle. Parts: $30-60 for the gasket. Labour: 2-3 hours.

Question 11

DOD/AFM Lifter Collapse (VZ LS2 with DOD)

Accepted Answer

Misfiring on specific cylinders, rough idle, check engine light. Metallic knocking from inside the engine. The VZ LS2 (some models) features Displacement on Demand (DOD), which deactivates four cylinders under light load. The DOD lifters use an internal locking mechanism that can fail, causing the lifter to collapse and the valve to not open. This is a known GM design issue affecting LS engines with DOD/AFM worldwide. Replace the failed lifters. Many owners replace all lifters with non-DOD lifters and have the DOD system disabled via an ECU tune. This is the recommended long-term fix, it eliminates the problem permanently. Parts: $300-500 for non-DOD lifters. Tune to disable DOD: $200-400.

Question 12

4L60-E Automatic Issues

Accepted Answer

Harsh 1-2 shift, delayed engagement from Park to Drive, slipping under hard acceleration, shudder during torque converter lockup. The 4L60-E is a hydraulically controlled (VN-VS) or electronically controlled (VT-VZ) 4-speed automatic. The 3-4 clutch pack and the torque converter clutch are the primary wear items. Contaminated fluid, infrequent service, and high-power applications accelerate wear. Service the transmission (fluid and filter) every 40,000 km. If the transmission is already showing symptoms, a shift kit ($200-400 fitted) can extend life. A full rebuild costs $1,500-3,000. For high-power applications (modified LS1/LS2), the 4L60-E is marginal, consider a 4L80-E swap or a built 4L60-E with upgraded internals.

Question 13

Manual Gearbox Synchro Wear

Accepted Answer

Grinding or crunching when shifting into 2nd or 3rd gear, especially on cold mornings or when shifting quickly. Synchro rings wear with age and mileage. The T56 6-speed manual (VT II onwards) is generally robust, but 2nd-gear synchro wear is the most common complaint. Aggressive downshifting accelerates wear. Synchro replacement requires the gearbox to be removed and partially disassembled. Budget $800-1,500 for a synchro rebuild. Using quality gearbox oil (Motul or Penrite) and changing it every 40,000 km helps prevent premature wear.

Question 14

IRS Bush Wear (VN onwards)

Accepted Answer

Clunking from the rear over bumps. Rear-end wander, particularly under braking. Uneven rear tyre wear. The car feels vague in the rear. The independent rear suspension uses rubber bushings in the trailing arms, lower control arms, and differential mount that deteriorate with age. Road conditions, load, and spirited driving all accelerate wear. This is the most common suspension issue on all Commodores from the VN onwards. Replace the rear bushings. A full IRS bush kit (all trailing arm bushings, diff mount bushings, and lower control arm bushings) costs $200-500 in parts. Labour: 4-8 hours. Nolathane and SuperPro both offer polyurethane bush kits that last significantly longer than rubber. Whiteline offers a complete rear bush kit that's popular with enthusiasts.

Question 15

Power Steering Rack Leak (VT-VZ)

Accepted Answer

Power steering fluid on the garage floor, heavy steering at parking speeds, whining from the power steering pump. The power steering rack seals wear with age. The VT-VZ rack is a well-made unit, but seals deteriorate after 15+ years. Low fluid from the leak accelerates pump wear. Replace or recondition the steering rack. A reconditioned rack is $300-500 exchange. New racks are $500-800. Labour: 3-5 hours.

Question 16

Front Strut Top Mount Failure (VT-VZ)

Accepted Answer

Clunking noise when turning the steering wheel, particularly at low speeds and full lock. A "crunching" sensation felt through the steering wheel. The rubber bearing in the front strut top mount deteriorates. The metal bearing inside can also corrode and bind. Replace the front strut top mounts. Parts: $80-150 per side. Replace the struts at the same time if they're leaking or have high mileage. Total front suspension refresh (struts, top mounts, control arm bushings, tie rod ends): $800-1,500.

Question 17

Body Control Module (BCM) Issues (VT-VZ)

Accepted Answer

Intermittent electrical faults, interior lights stay on, power windows stop working, central locking misbehaves, dashboard warning lights illuminate randomly, the car may not crank. The BCM is the central control module for the body electrics. It communicates with the engine control module (ECM), instrument cluster, and various sub-systems via CAN-bus wiring. The BCM can develop internal faults from age, moisture ingress, or power surges. The connector pins can also corrode. Diagnosis first, a Tech2 or compatible scan tool can read BCM fault codes. Connector cleaning sometimes resolves intermittent issues. A faulty BCM must be replaced and programmed to the car's VIN and immobiliser system. A secondhand BCM needs programming: $100-200 at an auto electrician. A new BCM from the dealer (where available) is $300-600.

Question 18

Alternator Failure

Accepted Answer

Battery warning light on the dash, dim headlights, accessories losing power, battery going flat. The alternator wears with age. The VT-VZ alternator operates at high output to support the car's electrical demands. Internal rectifier and regulator failure are the most common modes. Replace the alternator. Test output first: 13.8-14.4V at idle with accessories off. VN-VS alternators are straightforward to replace. VT-VZ alternators are slightly more difficult due to packaging but still a 1-2 hour job. Parts: $200-400.

Question 19

VN-VP Boot Floor and Sill Rust

Accepted Answer

Rust perforations in the boot floor, sills, and rear wheel arches. Water in the boot, bubbling paint along the sills. Same as every Australian car of the era, water ingress through taillight seals, stone chip damage, and trapped moisture in enclosed sections. Cut out and weld in repair panels. Treat surface rust early with rust converter and sealer. Professional sill repair: $1,500-4,000 per side.

Question 20

Paint Peel (VT-VX, specific colours)

Accepted Answer

Clear coat peels from the roof, bonnet, and boot lid. Paint appears chalky and dull before peeling. Certain VT-VX paint colours (particularly some metallics) suffered from clear coat adhesion problems. UV exposure and poor factory prep contribute. The VT-VX is more affected than the VY-VZ. The only proper fix is a respray of the affected panels. Budget $1,500-3,000 for a quality respray of the roof, bonnet, and boot. Alternatively, a cut-and-polish can delay peeling if the clear coat is just beginning to cloud.

Commodore (VN-VZ) / HSV

Commodore (VN-VZ) / HSV known problems