Mercury - Oil Change Kit, 25/30HP EFI FourStroke, 2 Liters Maintenance 8M0081915. Overview. These 25 and 30HP Mercury EFI four-strokes are tough little engines, but they definitely let you know when the oil's getting tired. They idle a lot, they take plenty of short bursts to full throttle, and they run warm for their size. This kit keeps the whole oil-change job simple-two bottles of the right 25W-40 oil, the proper filter, a new drain plug seal, and a drip tray so you're not chasing oil across