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The advantage of common rail diesel injection over direct injection is the fact that you have less engine noise and reduces exhaust emissions even further. The diesel engine also has a much higher compression ratio compared to petrol engines. Diesel 17:1 Petrol 11:1. That is why some diesel cars needs oil replacement every 7500 km. Depending of the type of oil they use and the quality of diesel used they push up the service interval. The diesel engine weirs out the oil quicker because of the high compression and the high heat of the turbo charger. That is why the diesel engine oil is always very black, compared to petrol engine oil. It is not good to drive a diesel engine very hard and then just switch it off. You can damage the turbo charger if you do that (all that heat and then no cooling). The turbo also has variable vanes controlled by the engine management system. The BMW 320d is one of the most advanced, most powerful and most economical diesel engines in its size.
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