HI, have nn GSI 16V, which flaps a bit. When I bought it with 154,000 was probably no special oil in it (predecessor was probably a heather, is champion at Opel but not cared for the car ) especially since I do not know if the mileage power is right, because my predecessor should have driven around with a analogue tacho ( first experienced later ). Since the engine clacked and I wanted to do him something good, I put Costrol 0W40 in it. With that he had a good fuel consumption, approved s But I got 1 l of oil on 1000 km and clapped more and more extreme. At 169,000 (this April, summer vehicle ) now brand new Hydotschall came in ( + again new oil Castrol Formula RS 0W40 – the oil also had the engine quite cleaned ) and it became considerably quieter, but it was not completely away either. After about 700 km it became again increasingly louder, so after another 300 km I had had enough and 15W40 got inside. This made it a little quieter again. After 7000 km new 15W4 0 pure, a little quieter again. Now ( 180,000 km ) he has remained on a stand ( volume ) and I wonder if the new bumps might have got rid of a Macke again by the thin oil (maybe he is also not much louder than directly after the change, but something I think ) . But is quieter than before and I can live with the sounds – become with warm engine also quieter and the engine goes really animaly. Then I am now dr because my engine didn’t notice the full-synthetic 0W40, so the fully synthetic 10W60 doesn’t necessarily like it either, or ? Besides, it doesn’t just depend on the viscosity, but also on the API classes or ? 0 W or 5 W are funny or ? And 40 in the back has my 15 W 40 as well as a 5W40 or 0w40 or 10W40. The 60 in the 10W60 only need very bad heaters or ? And with the API classes that I’ve been told to specify the quality reached my now oil Castrol GTX 3 15W40 with SJ not quite the 0W40, but comes already close and exceeds the required SF or SG (oil cover ) by far. But why do you read partly in forums that Opel would have prescribed a partial synthetic for this engine? I think that I can get away better with a very good 15W40. Do you have experiences on the topic ? mfg gsi-man