Mercury - 80W-90 Premium Gear Lube Outboards and Sterndrives Marine Formula 858059K01. Overview. There is a kind of comfort that only comes from knowing your gear can take a beating and still perform like new. Mercury 80W-90 Premium Gear Lube delivers exactly that - protection you can trust, mile after mile on the water. It is designed for boaters who don't baby their engines, who run hard, who push through waves without hesitation. This oil doesn't just lubricate; it gives your lower unit the c