Sierra Gear Lube Adapter 18-9794, Replaces Mercury 91-883704Q03, Fits Nissan Yamaha Honda Tohatsu Outboards

The Sierra 18-9794 Gear Lube Adapter is a tapered, unthreaded hose end fitting that lets you fill an outboard lower unit with gear lube using a Sierra quart pump or a lower unit fill tube. It is designed for use with Sierra's 18-9600-5, 18-9620-5, and 18-9650-5 quart pumps, giving you a secure, drip-resistant connection between the pump hose and the lower unit fill port. The adapter is built with a metric 8-1.25 thread to match the fill port thread pattern on compatible outboards, and it replaces Mercury part number 91-883704Q03, making it a direct-fit swap when servicing lower units that call for that Mercury adapter. It is intended for use on Nissan, Yamaha, Honda, and Tohatsu outboard lower units, covering a wide range of common outboard brands serviced in the field or in the shop. Because the fitting is tapered and unthreaded at the hose end, it seats into the pump hose without requiring additional clamps or threading, simplifying routine gear lube changes and reducing spill risk during service. This adapter is a small but essential accessory for anyone performing regular lower unit maintenance, and it is sized to work alongside standard Sierra quart pump equipment already used in most marine service bays.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-9794
• Product Type: Gear Lube Adapter
• End Style: Tapered, unthreaded hose end
• Thread Size: Metric 8-1.25
• Used With: Sierra 18-9600-5, 18-9620-5, and 18-9650-5 quart pumps, or lower unit fill tubes
• Item Dimensions: 0.6 inches L x 2 inches W x 0.5 inches H
• Weight: 0.03 pounds
• Package Quantity: 1

Fitment

• Nissan outboards
• Yamaha outboards
• Honda outboards
• Tohatsu outboards

Replaces (OEM)

• Mercury 91-883704Q03

Frequently Asked Questions

What is the Sierra 18-9794 Gear Lube Adapter used for? It connects a Sierra quart pump or lower unit fill tube to an outboard's gear lube fill port, letting you add or change lower unit gear lube without spilling or having to thread a separate fitting.

Which outboard brands does the 18-9794 fit? This adapter is designed for Nissan, Yamaha, Honda, and Tohatsu outboard lower units.

What Mercury part number does the 18-9794 replace? The Sierra 18-9794 replaces Mercury part number 91-883704Q03, so it can be used as a direct substitute where that Mercury adapter is called for.

What thread size does this gear lube adapter have? The 18-9794 uses a metric 8-1.25 thread to match the fill port on compatible outboard lower units.

Is the hose end threaded or unthreaded on the 18-9794? The hose end of the 18-9794 is tapered and unthreaded, so it seats into the pump hose without needing extra clamps or threading.

Which Sierra pumps does the 18-9794 adapter work with? It is designed for use with Sierra's 18-9600-5, 18-9620-5, and 18-9650-5 quart pumps, as well as standard lower unit fill tubes.

How much does the 18-9794 adapter weigh? The Sierra 18-9794 Gear Lube Adapter weighs 0.03 pounds.

What are the dimensions of the 18-9794? The adapter measures 0.6 inches long by 2 inches wide by 0.5 inches high.

Does the 18-9794 fit Suzuki lower units? No, the 18-9794 is designed for Nissan, Yamaha, Honda, and Tohatsu lower units; Suzuki lower units use the separate Sierra 18-9795 adapter with a metric 10-1.25 thread.

How many adapters come in the package? Each Sierra 18-9794 order includes one gear lube adapter (package quantity of 1).

Is the Sierra 18-9794 an OEM or aftermarket part? The 18-9794 is a Sierra-branded adapter engineered to replace Mercury 91-883704Q03, offering equivalent fit and function to the original Mercury adapter.