[Web Creator] [LMSOFT]
VT Commodore Engine Issues
Phoenix Mechanical

Gen III Pistons - There are plenty of Gen III's that have never had any oiling issues, whereas there are some that have had excessive oil consumption issues. As we all know, "Bad news" travels twice as fast as "Good news". Apparently GM has changed the piston and ring design 3 times (to suit Australian fuels and oils not USA's) to try to get the oil consumption down, without impeding power or noise. Gen III engines are quite often noisy/rattly when cold (piston or gudgeon noise), which is a result of assembly tolerances. Those types of noises should be reduced as the engine and oil warms.

Gen III Oil Problems - During a cold start-up, a GEN III should have more than 150kpa of oil pressure. If there is less than that, GMH suggest further action, which usually results in the engine being removed. Once the engine is removed, the oil pump is replaced, and the pickup tube o-ring is changed. This procedure is recommended to be carried out with the engine out of the vehicle to ensure the correct refitting of the sump.

Australian Gen III's have a front mounted oil pickup and sump design, where as the Gen III's originally (US) had a rear mounted pickup and sump design. A downside to this is that under hard acceleration, the oil pump pickup may not be submersed in enough oil, so the oil system momentarily aerates. During hard acceleration, zero or extremely low oil pressure will easily damage any crank bearings. That applies to any engine.

Gen III Oil Consumption - Oil consumption has been found to be reasonably higher than previous models, with 2.5Ltrs per 10,000Km's being the acceptable limit.

Gen III Oil leaks - On the front left edge of the engine sump, there is a oil pan transfer cover (just above the oil filter). Some Gen III's may leak oil from this area. A possible caused can be porosity in the oil pan transfer cover stud holes. A revised sump was introduced early in 2000. O-Rings were added to the oil pan transfer cover studs (with a gasket as well), to help reduce leaks from this area. In some situations, the sump itself can be porous, and may need to be replaced.

Unfortunately, early production sumps can not have O rings fitted to them, as they have not been counter bored around the transfer cover mounting studs.

Gen III Coolant Leaks - Gen III's have a coolant crossover pipe located below and behind the radiator. The hoses were connected using spring band type clamps. In some cases, these clamps are insufficient, and coolant may leak from this area. Worm drive hose clamps for the cross-over pipe hose connections (larger radiator hoses) have been fitted to vehicles (during production) from mid 2000.

Hose Clamp - Part number 92138604

Gen III Engine Covers - Engine cover rattle at idle, or just above idle speed is common. This is caused by the engine cover contacting the coil/bracket assembly. GMH have revised the support brackets and the mounting nuts. Split covers are readily available which reduce inlet manifold temperature for better performance. In mid 2002, the brackets were again revised with bumpers, and no longer require spacer nuts.

RH Engine Cover Support Bracket (includes new bumper 92138641) - Part number 92087580

LH Engine Cover support Bracket (includes new bumper 92138641) - Part number 92087581

Bumper (15mm high, slotted) - Part number 92138641

Nut - Part number 09440004 

Engine cover Insulator (front) - Part number 92086029

The engine cover may also rattle against the hydraulic clutch hose on manuals built before vin # L867194. The clutch hoses may become twisted or distorted and interfere with the engine cover. A revised clutch hose with quick-connect fittings was introduced mid 2002.

Gen III Vibration - Some VT's may suffer from an excessive vibration, which is felt within the vehicle. Vibrations may be felt when A. The vehicle is stationary with the engine idling in gear and the A/C is on , B. When the idle speed drops during automatic gear selection and/or a steering load is applied, or C. During slow acceleration or low speed driving in a low gear, with engine speed between 650 and 1000 rpm. Several areas may cause these issues. One area is the PCM calibration, which was later revised with improved idle speed control. Another area may be a stressed exhaust system. A Bent catalytic converter bracket is an indication that exhaust stress is evident (this should be straight). Spacers can be added to keep this bracket straight when bolted in place.

Catalytic Converter bracket bolt - Part number 90495649
Flat washer (spacer) - Part number 120394

Along with a sequence of loosening and retightening exhaust and mount bolts, extra bolts were added to the rear gearbox mount.

Gearbox mount bolt - Part number 92138301
Gearbox mount nut - Part number 11086962 (torque to 45-55 Nm)

Gen III Belt Squeal - In some cases, Gen III engine serpentine belts will squeal at around 1500 to 1900 rpms. The squeal can occur if the power steering pump pulley is misaligned with the crank pulley and the alternator pulley. The pump pulley may be too close to the pump body or too far forward. This can cause the belt to not track straight and will rub on the front or rear flange of the pulley. An adjustment of the power steering pump pulley (between 1 – 3mm) may be required, to re-align the pulleys.

Some Gen III Automatics may develop a belt chirp/squeal under hard acceleration, during the 1-2 shift.
Decreased damping of the belt tensioner increases this condition, so a revised belt tensioner with increased damping was introduced early 2002.

Belt Tensioner - Part No 92111701

V6 Engine Pulley noise - Some V6 engine pulleys develop a ringing type noise at idle, which may be caused by the drive belt slapping against the A/C idler pulley. A revised A/C idler pulley was introduced late 2000.

Idler pulley Assembly - Part number 92094003
Idler pulley support - Part number 92065824
Drive belt - Part number 92100691

Belt Squeal (SC V6) - The supercharger belt may squeal or chirp during cold start conditions, if the belt is old or if the pulleys are misaligned.

Supercharger Drive Belt - Part number 92067829

Rear Main seal - VT Commodore rear main seals are one piece, and are located in an alloy plate that can be removed from the engine block. A special GMH tool is used for correct reinstallation and aligning of the seal plate. Hot engine oil and age reduces the seals ability to work effectively, and this can result in an oil leak from the back of the crankshaft. These are commonly replaced by removing the transmission, instead of removing the engine.

Poor performance up hill (V6) - Some VT's may feel to have a lack of power or lack of response when driving at approximately 70-85km/h in 4th gear, and generally when driving up inclines. The original Transmission and Memcal calibration required allot of throttle opening before the car would kick down a gear, or the driver would have to manually select a lower gear. The original calibration was designed to achieve optimum fuel economy at those speeds and conditions, but a revised Memcal with improved shift patterns was introduced mid 2000 to overcome these issues.

V6 Memcal - Part number 12203180 (DJLX)

Notchy Accelerator Pedal - Some VT V6's may have a notchy feel to the accelerator pedal. Replacement of cable, or attempts to re-route the cable do not improve the feel. A revised accelerator cable was introduced mid 1999, which was shorter (routed differently as well), and had less friction between the inner and outer cables.

V6 Accelerator Cable - Part number 92082648

Rough Idle or Hissing noise (V6) - Rough engine idle may be experienced, or a hissing noise may be heard from the engine compartment. In many cases, the hose between the throttle body and purge solenoid may come apart. A revised hose was introduced, with improved temperature tolerance adhesive.

Purge Hose - Part number 92102345

Rough Idle or Hissing Noise (Gen III) - Some Gen III's may experience rough idle, a high pitched hissing noise and the engine check lamp illuminates on the dash. The PCV (positive cranck case ventilation) pipe may deteriorate, perish and fail causing these problems. A revised PCV pipe made of more durable material was released.

PCV Pipe – Part number 12590632

Cam and lifters 5.0ltr V8 - VT 5.0ltrs have a roller cam, and use roller lifters. The roller cam design dramatically reduces valve train loads. Roller lifters are positively located in their bores by aligning plates, so that they cannot rotate like conventional lifters. The aligning plates are held down by a metal plate so that they cannot move. I have had several instances where the metal plate has broken, and the aligning plates have been allowed to move out of place. This results in the lifters rotating, which damages both the lifter and the cam lobes.  Major problems can arise when cam lobes wear down, as insufficient lobe lift will restrict valve opening and therefore cylinder operation. After many kilometres, V8 cams and lifters wear naturally, but can equate in reduced engine power and noisy valve train operation.

Rocker gear 5.0ltr V8 - Rocker gear wear is inevitable. Alloy rocker bridges and steel rockers arms wear with age, and wear increases noise and reduces valve lift. New rocker arms and bridges are available.

Petrol Filler Cap - VT's fitted with LPG need a smaller petrol filler cap (92077227, and are grey in colour), which increase the room available to remove either the LPG cap or Fuel cap.

Fuel Tank Capacities - For 1997 Models: Dry 70ltrs, When distance to empty is zero 60-64 ltrs, When low fuel warning chime sounds 58-62 ltrs. For 1998 Models: Dry 75ltrs, When distance to empty is zero 65-69 ltrs, when low fuel warning chime sounds 63-67 ltrs.