STAR BRITE Synthetic Blend Lower Unit Gear Lube 80W-90 Marine-Grade, GL-5/MT-1 Protection

STAR BRITE Synthetic Blend Lower Unit Gear Lube 80W-90 is a marine-grade gear oil engineered to protect outboard and sterndrive lower units from wear, rust, and thermal breakdown under heavy load conditions.

When you need a dependable gear lubricant for engines over 100 hp, this 80W-90 synthetic blend meets API GL-5, API MT-1, SAE J2360 and Mack GO-J performance specifications. Formulated with extreme-pressure and anti-wear additives, it delivers stable viscosity at operating temperatures and reduces metal-to-metal contact in marine gear sets. STAR BRITE packages this formula with installation guidance and a line of accessories to simplify oil changes on boats and personal watercraft.

How does this gear lube protect a lower unit under heavy use?

The blend contains high-viscosity base stocks and extreme-pressure additives that build a durable film between gear teeth, reducing friction and wear during hard acceleration and prolonged runs. Corrosion inhibitors help prevent rust in wet, salty environments common to marine use.

• 80W-90 viscosity for consistent film strength across temperature ranges
• API GL-5 and MT-1 rated for hypoid and marine gear service
• Added anti-wear and extreme-pressure compounds for load-bearing protection
• Rust and corrosion inhibitors formulated for marine exposure

Will this oil fit my boat’s lower unit and service needs?

STAR BRITE 80W-90 is intended for lower units and gearcases that specify an 80W-90 grade or GL-5/MT-1 service rating and is especially recommended for engines over 100 hp. Always check your engine manufacturer’s manual for the required specification and capacity before use.

• Compatible with systems calling for API GL-5, MT-1, SAE J2360 or Mack GO-J
• Recommended for most outboards, sterndrives, and heavy-duty gearcases over 100 hp
• Available alongside pumps, fill tubes, and adapters for correct fitment
• Serves as an upgrade option over conventional lower unit oils

How do I change the lower unit oil with this product?

Drain the old lubricant, install the fill tube or appropriate adapter, then refill to the manufacturer’s specified level and replace the drain and fill plugs. STAR BRITE supplies step-by-step guidance and accessories that make the process cleaner and faster.

• Flush the gearcase if contaminated before refilling
• Use STAR BRITE quart pumps or lube tubes to avoid spills
• Refill until lubricant slightly exits the fill port to confirm proper level
• Dispose of used oil responsibly according to local regulations

What performance benefits should I expect on long outings?

The synthetic blend offers thermal stability that helps resist viscosity breakdown during extended high-speed operation, which maintains gear protection and can reduce noisy gear whine. Over time, reduced wear and corrosion can extend component life and help prevent unexpected failures while underway.

• Improved thermal stability for long runs and hot conditions
• Lower friction for smoother gear engagement and quieter operation
• Corrosion resistance for salt and fresh water longevity
• Compatible with common marine service schedules and maintenance practices

Who is this for: Boaters and marine technicians who maintain outboards, sterndrives or other lower units that call for 80W-90 GL-5/MT-1 gear oil—especially owners of vessels over 100 hp who demand longer-term protection, easier servicing, and proven marine-grade additives. If you want a straightforward upgrade from conventional lower unit oils and access to fill tools and pumps from the same brand, STAR BRITE’s Synthetic Blend 80W-90 is designed for that use.