Sierra Marine Water Pump Impeller Kit 18-3077 – MerCruiser / OMC Raw 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 Water Pump Impeller Kit is a complete service kit designed to restore proper cooling system performance in MerCruiser and OMC marine engines. This kit includes a high-quality flexible impeller along with essential gaskets, O-rings, and seals needed to service the raw water pump.
The impeller is responsible for circulating cooling water through the engine. Over time, the rubber vanes can wear, harden, or break down, reducing water flow and increasing the risk of overheating. Replacing the impeller and sealing components ensures reliable cooling and helps protect your engine from damage.
Manufactured to meet or exceed OEM specifications, this kit delivers dependable performance in both freshwater and saltwater environments.
Key Features
- Complete raw water pump impeller service kit
- Includes impeller, gasket, O-ring, and seals
- Restores proper cooling water circulation
- OEM-equivalent fit and performance
- Durable marine-grade rubber impeller
- Sierra limited lifetime warranty
Engine Compatibility
MerCruiser Engines
- Alpha One (Gen I)
- MR drives
- Select MerCruiser sterndrive engines
OMC Sterndrives
- Stringer drives
- Select OMC applications
➡️ Designed for engines using compatible raw water pump assemblies
Serial Number Fitment Notice
Fitment depends on:
- Drive type (Alpha / MR / OMC)
- Pump housing configuration
- Engine serial number
⚠️ Always confirm using:
- Engine serial number
- OEM part number match (18-3077)
When This Part Needs Replacement
Replace the impeller kit if you notice:
- Weak or no water flow
- Engine overheating
- Cracked, missing, or stiff impeller vanes
- Reduced cooling efficiency
- After seasonal storage
Recommended service interval: every 100 hours or annually
Installation Notes
- Lubricate impeller before installation
- Install with correct vane rotation
- Replace all included seals and gaskets
- Inspect pump housing and wear plate
- Ensure proper key alignment on shaft
Alternate / Superseded Part Numbers
OEM Cross References
- Mercury / MerCruiser: 47-89984T4, 47-89984T2
- OMC: 777128, 3854286
Aftermarket Cross References
- Sierra: 18-3077
- Mallory: 9-45605
- GLM: 12024
Shipping
Shipping: Ships same or next day for fast Canada wide shipping. ⚓
💡 Parts Desk Insight
On Alpha and older OMC drives, the impeller is the first thing to go when cooling issues start. Even if it still looks okay, the rubber can lose flexibility and reduce water flow under load.
Doing the full kit instead of just the impeller helps ensure proper sealing and longer-lasting performance 👍
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.