Mobil One Del Vac has the highest rating of all diesel oils. Over the last few years most MFG's have changed their thinking on?synthetic oil and are now recommending it. Some like Mercedes and BMW and others are putting it in at the factory. PLEASE UNDERSTAND THAT MOBIL?DEL VAC 1 ?DIESEL OIL ..........IS NOT THE MOBIL ONE THAT YOU FIND IN GAS STATIONS AND RETAIL STORES. YOU CAN ONLY GET IT AT COMMERCIAL OIL DISTRIBUTORS AND A FEW LARGE MARINAS CARRY IT. Here is a link you can use http://www.mobil.com/USA-English/Lubes/PDS/GLXXENCVLMOMobil_Delvac_1_5W-40.asp ? Bob Ocean Rose