Contrary to internet chatter and uninformed speculation, there’s no difference in engine or fuel management between an ST200 and GSis developed by MSD. The basic engine is a 2.5-litre 54° V6, albeit one equipped with higher lift ‘G’ inlet cams as found in the three-litre Omega V6. Along with the aforementioned Irmscher silencer, the change boosted power to a naturally aspirated 192bhp and 193lb/ft torque.
When the ST200 was launched, promotional literature suggested the model was the recipient of updated ECU software. This is untrue, although Vauxhall did intend to make the change when it was assumed pre-orders for the ST200 would come thick and fast.
In essence, the X25XE is a strong, reliable powerplant if looked after and serviced regularly. Timing belt and water pump renewal intervals are 40k miles, although factory handbooks state 80k miles. Ignore that information; the manufacturer soon changed its tune when dozens of broken engines needed to be replaced under warranty due to premature snapping of rubber belts! Changing the timing equipment isn’t a particularly expensive job, but it can be a major headache if you haven’t got camshaft locking tools or other necessary apparatus at your disposal. Our advice would be to hand the work over to a mechanic well-versed in the maintenance of Vauxhall V6 engines.
Complaints associated with the 54° V6 powerplants are few and far between. The oil cooler is buried between cylinder heads and is known to corrode, leading to the leaking of oil into the cooling system. Oil in the expansion tank is a sure-fire sign of failure. Don’t be tricked into thinking you’re looking at head gasket failure (which you can identify from detecting water in the oil), although these parts can be prone to giving up the ghost if a 50/50 concentrated mix of coolant isn’t observed.
Misfire underload can be down to knackered (or cheapo) ignition leads or a faulty coilpack. The parts are readily available due to Vauxhall V6 engines being produced in such high numbers for use in a variety of models, including Cavaliers, Calibras and Omegas. Additionally, mass airflow meters (MAF) and sensors providing camshaft, lambda and knock information can fail with age, resulting in poor engine operation and the illumination of the engine management light. Again, all parts are easily available from retailers, such as Nevlock, Autovaux and Genuine Part Search.
If possible, get a mate with a Tech 2 or OPCOM diagnostic tool to check the stored fault codes in the car’s ECU. This will highlight any existing complaints. If you do buy the car you’re looking at, it might be worth clearing all registered fault codes (after you’ve made a note of them) so that you can see which ones return as current complaints, prompting further investigation.