West Marine Fuel/Water Separating Filter — 1778 | Sierra 18-7789
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The West Marine 1778 Fuel Water Separating Filter is a marine spin-on replacement filter element designed for compatible gasoline fuel/water separator heads. Commonly cross-referenced with Sierra Marine 18-7789, this filter helps protect Volvo Penta, OMC Cobra, and compatible marine fuel systems by reducing water and particulate contamination before fuel reaches the engine.
This is a replacement spin-on filter element only. It does not include the filter head, mounting bracket, fittings, hoses, primer components, or complete fuel/water separator assembly.
Key Features
- Marine spin-on fuel/water separating replacement filter.
- West Marine part number: 1778.
- Sierra Marine cross-reference: 18-7789.
- Designed for compatible Volvo Penta and OMC Cobra sterndrive fuel systems where listed.
- Helps separate water from gasoline before it reaches the engine.
- Helps capture fine particulate contamination and fuel-system debris.
- Filtration rating: 21 micron.
- Water separation reference: up to 99% where system conditions and filter application support that performance.
- Epoxy-coated canister construction for marine corrosion resistance.
- Built for damp bilge and engine-room environments.
- Designed for gasoline fuel applications.
- Compatible with pre-mixed 2-cycle fuel applications where this filter is specified.
Fuel System Compatibility
Common application context includes compatible marine fuel/water separator systems used with:
- Volvo Penta gasoline sterndrive applications where listed.
- OMC Cobra sterndrive applications where listed.
- Marine gasoline fuel systems using a matching spin-on separator head.
- Fuel/water separator assemblies that call for West Marine 1778, Sierra 18-7789, or a verified equivalent.
- Ethanol-blended marine fuel systems where water separation and particulate filtration are required.
Use this filter only where the existing filter number, filter head thread, gasket diameter, fuel type, flow requirement, and engine service information confirm compatibility.
Fitment Notice
Confirm fitment by matching the existing filter part number, separator head, thread size, gasket diameter, canister clearance, fuel type, and required fuel-flow capacity before ordering. Marine fuel/water separating filters can look similar but may differ in thread, gasket fit, canister size, micron rating, and flow performance.
This filter is not a universal fuel filter and should only be used on compatible fuel/water separator assemblies.
When This Part Needs Replacement
Replace the fuel/water separating filter during seasonal service, after contaminated fuel exposure, after water is found in the fuel system, or when the engine shows signs of fuel restriction such as hard starting, rough idle, hesitation, surging, loss of power, or stalling under load.
Replacement is also recommended if the canister is rusted, dented, leaking, clogged, or past the engine manufacturer's recommended service interval.
Installation Notes
Shut off the fuel supply before servicing the separator. Place absorbent material under the filter, remove the old filter, and confirm the old gasket is not stuck to the filter head. Clean the sealing surface before installing the new filter.
Lightly lubricate the new gasket with clean fuel or engine oil, install the filter by hand, and tighten according to the filter head or engine service instructions. Do not over-tighten. After installation, prime the fuel system, check carefully for leaks, and run the engine while inspecting all fuel connections.
Dispose of the used filter and any contaminated fuel according to local environmental requirements.
Alternate / Cross-Reference Part Numbers
- West Marine 1778 — primary supplied part number
- Sierra Marine 18-7789 — cross-reference reference
- Volvo Penta 3851218-2 — cross-reference reference; verify by engine model
- Volvo Penta 3852413 — cross-reference reference; verify by engine model
- Volvo Penta 3852418 — cross-reference reference; verify by engine model
- Volvo Penta 3862228 — cross-reference reference; verify by engine model
Parts Desk Insight
This filter should be matched by the existing filter number and separator head, not by engine brand alone. The correct replacement must seal properly to the fuel/water separator head and provide the required fuel flow for the engine. If water is found in the removed filter, inspect the fuel tank and fuel supply source before returning the boat to regular use.
Shipping: Ships same or next day for fast Canada wide shipping. ⚓
Part Number: 1778 | SKU: SIE-18-7789
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.