Mobil Delvac™ HDEO 15W-40 and 10W-30 are synthetic blend diesel engine oils designed to meet warranty requirements for high-speed, four-stroke heavy duty diesel engines. Mobil Delvac™ HDEO 15W-40 and 10W-30 are oils designed to meet warranty requirements for high-speed, four-stroke heavy duty diesel engines. These products are formulated to maintain the durability of emission control systems, including diesel particulate filters and other advanced aftertreatment systems.