dont know a lot about the 440 diesels,but certainly with the s40 theres a known issue about them needing regular decokes.this is a big problem because volvo owners like their high mileages. some dealers recommend avoiding the s40 diesel which i think is a mitsubishi engine. i dont remember seeing many 440 diesels.if your considering one rather than having one,i suspect the servicing costs are higher which eats into the fuel savings,or wipes them out altogether.if this is so,the diesel which is slightly less refined and slower than the petrol engine,does not make a good financial proposition