Water and gear lube don’t mix, but you can’t avoid submerging your marine motor’s lower unit. Water can breach the seals and contaminate the gear lube in the lower unit, causing problems.
Gear lube contaminated with water can fail to protect
Water contamination is bad for several reasons.
Viscosity loss – A lubricant’s viscosity is its most important property. While viscosity is defined as resistance to flow, it’s helpful to think of it as the lubricant’s thickness. Your marine motor’s lower unit is designed to use a gear lube of a specific viscosity for optimal wear protection. Water can reduce the gear lube’s viscosity below what the manufacturer recommends, reducing wear protection.
Foam – A film of gear lube forms on the gear teeth it protects. This fluid film absorbs pressure and prevents metal-to-metal contact. Water contamination, however, invites the formation of foam. As the foam bubbles travel between gear teeth, they rupture under the intense pressure, leaving nothing behind to guard against wear. Eventually, the gears can wear out and require replacement.
Sludge – Water produces sludge, which inhibits heat transfer and increases lubricant temperature. Elevated temperatures speed chemical breakdown (known as oxidation). The faster the lubricant breaks down, the sooner it fails to provide adequate protection – and the sooner it must be changed, wasting money.
Rust formation – Water contamination invites rust formation on metal surfaces. Rust can flake off and circulate throughout the gear lube, where it acts like sandpaper and scours bearing and gear surfaces.
Severe service worsens the problem
Marine motors often operate under extreme conditions that further stress the lubricant. Frequent throttle bursts concentrate tremendous pressure on the pinion gear and the forward and reverse gears. The gear lube fluid film can rupture, especially if it’s been weakened due to water contamination, leading to metal-to-metal contact.
AMSOIL offers a solution
Avoiding contact with water is impossible when boating or fishing. That’s why we formulate AMSOIL Synthetic Marine Gear Lube to deliver advanced outboard protection against power loss and gear wear, even with up to 10 percent water contamination.¹
With AMSOIL, you can rest assured your marine motor is protected and equipped to handle whatever conditions you throw at it.
¹Based upon AMSOIL testing of AMSOIL Synthetic Marine Gear Lube 75W-90 in ASTM D892.