Sierra Impeller Kit 18-3077 (AP-1933) – Mercury / Mariner Outboard Water Pump Service Kit
Free returns on all eligible orders
You have 30 days to request a return. All sale items are final sale.
The Sierra 18-3077 Impeller Kit (AP-1933) is a complete raw water pump service kit designed for Mercury and Mariner outboards. This kit includes the impeller and essential sealing components needed to restore proper cooling water circulation and prevent engine overheating.
The impeller is the primary wear component in the water pump system, responsible for drawing water through the lower unit and delivering it to the engine. Over time, the rubber vanes can wear, harden, or break down, reducing cooling efficiency.
Manufactured to meet or exceed OEM specifications, this kit ensures dependable performance and long service life in both freshwater and saltwater conditions.
Key Features
- Complete water pump impeller service kit
- Includes impeller and sealing components (varies by application)
- Restores proper cooling water flow
- Direct OEM replacement fit and performance
- Durable flexible rubber impeller construction
- Sierra limited lifetime warranty
Engine Compatibility
Mercury / Mariner Outboards
Commonly used on:
- 40 HP
- 45 HP
- 50 HP
- 60 HP
➡️ Fits select 2-stroke and early 4-stroke Mercury/Mariner outboards using compatible water pump housings.
Serial Number Fitment Notice
Fitment depends on:
- Engine model and year
- Lower unit / gearcase type
- Water pump housing configuration
⚠️ Always confirm using:
- Engine serial number
- OEM part number match (18-3077 / AP-1933)
When This Part Needs Replacement
Replace the impeller kit if you notice:
- Weak or no telltale stream
- Engine overheating
- Reduced cooling performance
- Cracked, hardened, or missing impeller vanes
- After seasonal storage
Recommended service interval: every 100 hours or annually
Installation Notes
- Install impeller with correct rotation direction
- Lubricate during installation
- Inspect wear plate and housing
- Replace all included seals/gaskets
- Ensure proper key alignment on shaft
Alternate / Superseded Part Numbers
OEM Cross References
- Mercury: 47-89983T, 47-89983, 89983T1
Aftermarket Cross References
- Sierra: 18-3077
- Mallory: 9-45601
- GLM: 12018
Shipping
Shipping: Ships same or next day for fast Canada wide shipping. ⚓
💡 Parts Desk Insight
If your outboard is still peeing but not as strong as it used to, the impeller is usually the first place to look. They wear gradually and often fail under load before showing obvious signs at idle.
Regular replacement keeps your engine running cool and avoids unexpected issues on the water 👍
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 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.