Sierra Hi-Performance Synthetic Blend Marine Gear Lube 18-9650-2 | 80W-90 GL-5 | 1 Quart
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18-9650-2 — Hi-Performance Synthetic Blend Marine Gear Lube
| Part Number | 18-9650-2 |
| Brand | Sierra Marine |
| Official Product Type | Marine Gear Lubricant — Synthetic Blend |
| Viscosity | SAE 80W-90 |
| API Specification | GL-5 |
| Container Size | 1 quart (946 mL) |
| UPC / Barcode | 030999969170 |
| System | Outboard Lower Unit / Sterndrive Gearcase |
| Supersedes | N/A — Sierra aftermarket product, not superseded |
| Replaced By | No replacement — 18-9650-2 is current |
What This Lubricant Does
Sierra 18-9650-2 is a synthetic-blend, SAE 80W-90, GL-5-rated marine gear lubricant formulated for the demanding conditions inside outboard lower units and sterndrive gearcases. Operating under high load, high RPM, and constant water-contamination risk, the gearcase is one of the most stress-loaded systems on a marine drivetrain. Sierra's synthetic-blend formula is designed to reduce operating friction while protecting gears, bearings, and sealing surfaces through extended service intervals and high-performance use.
Compatible Applications
- Outboard lower units requiring an SAE 80W-90 GL-5 marine gear lubricant
- I/O and sterndrive gearcases requiring an SAE 80W-90 GL-5 marine gear lubricant
- High-horsepower and high-performance marine propulsion systems
- Heavy-load applications where a synthetic-blend formulation is specified or preferred
Always confirm the viscosity grade and API specification required by your engine or drive manufacturer before ordering. Use 18-9650-2 where an SAE 80W-90 GL-5 marine gear lubricant is appropriate for your specific unit.
OEM Interchange References
Sierra lists 18-9650-2 as compatible with applications that specify the following OEM lubricants. These are Sierra interchange references only — 18-9650-2 is a Sierra aftermarket product, not an OEM-branded fluid.
- Mercury Marine: 92-858064K01, 8M0222063, 8M0222068
- Quicksilver: 92-858064Q01, 8M0222065, 8M0222067, 8M0222069
- Johnson / Evinrude (OMC): 778749, 778755
- Yamaha: ACC-GEARL-UB-QT
- Honda: 08739-90W
- Mallory: 9-82501
- Volvo Penta: 1141676 (cross-reference catalog)
Service Interval
Change lower-unit or sterndrive gear lubricant according to the engine or drive manufacturer's maintenance schedule. As a general marine service guideline, most manufacturers recommend annual gear-lube changes or replacement every 100 hours, whichever comes first. Always change gear lube immediately if inspection reveals:
- Milky or emulsified oil — indicates water intrusion through a failed seal
- Metallic contamination or debris
- Burnt or abnormal odour or colour
- Following any gearcase disassembly or seal service
If water is found in drained lubricant, inspect and service the gearcase sealing system before refilling — simply refilling without addressing the seal source will not resolve the underlying issue.
Service Notes
- Drain old lubricant completely and inspect condition before refilling
- Replace drain and fill screw sealing washers or gaskets where specified by the manufacturer
- Fill according to the manufacturer's procedure — fill from the bottom drain port until lubricant flows from the vent port
- Confirm required quantity for your specific drive; many outboards and sterndrives require more than one quart
- Check for water or metallic debris in the old lubricant as a diagnostic step
- Confirm drain and vent plugs are properly sealed after service
- Do not mix lubricant types or viscosity grades unless specifically permitted by the manufacturer
Technical FAQ
Q: Is this the same as standard 80W-90 automotive gear oil?
No. 18-9650-2 is a marine-specific formulation. Marine gearcases operate in water-rich environments with different seal materials and load profiles than automotive differentials. Always use a lubricant specified for marine use.
Q: Can I use this in place of my OEM gear lube?
Sierra lists this product as an interchange for the OEM numbers above. However, always verify the viscosity grade (80W-90) and API specification (GL-5) match what your engine or drive manufacturer requires. Check your service manual or manufacturer's maintenance guide before substituting any lubricant.
Q: How much do I need for a full lower unit service?
One quart (946 mL) is sufficient for most single outboard lower unit services. Larger outboards, sterndrives, and some counter-rotating drives may require more. Check the required fill volume in your engine or drive service manual before ordering.
Q: My drained gear lube was milky — should I just refill?
No. Milky gear lube indicates water intrusion through a compromised seal or gasket. Inspect and service the gearcase sealing system before refilling. A companion lower-unit seal service kit may be needed — see related products below.
Related Products
- Sierra Impeller Kit 18-3016-1 – Mercury / Mariner Outboard Water Pump Service Kit — combine with a gear lube change for a complete lower-unit service
- Sierra Marine Water Pump Impeller 18-3016-1 – Mercury / Mariner V6 Outboard Replacement
Parts Desk Insights
Best use case: 18-9650-2 is the right choice for annual lower-unit or sterndrive gearcase service where the manufacturer specifies an 80W-90 GL-5 marine gear lubricant. Its synthetic-blend formula makes it a strong option for high-performance and high-horsepower applications — particularly where loads and operating temperatures are elevated. Pairing a gear lube change with a water pump impeller service is one of the most effective annual maintenance combinations for outboard reliability.
Common issue: The most frequent customer question is whether one quart is enough for a complete service. For most standard outboards it is, but larger motors and sterndrives often require more. Direct customers to check their service manual for the required fill volume before ordering a single quart. Also: if a customer reports milky gear lube after drain, they need a seal inspection — not just a refill.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.