Sierra 18-7789 Fuel/Water Separating Filter | 21 Micron | Volvo Penta OMC
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Sierra 18-7789 Fuel/Water Separating Filter
- Part Number: 18-7789
- Brand: Sierra
- Official Product Type: Spin-on Fuel/Water Separating Filter
- Filtration Rating: 21 micron
- Thread: 13/16-18
- UPC: 808282244811
- Supersedes: Volvo Penta 3851218, 3852413, 3862228 — confirm by engine model and serial
- Replaced By: No confirmed supersession — 18-7789 is current Sierra catalog
- System: Gasoline marine fuel/water separation
- Service Interval: Annually or per engine manufacturer’s maintenance schedule; sooner after contaminated fuel exposure
What This Filter Does
The Sierra 18-7789 is a 21-micron spin-on fuel/water separating filter for compatible gasoline marine fuel systems. It removes separated water and fine particulate contamination from the fuel supply before it reaches the engine. The epoxy-coated canister is built for marine bilge and engine-room environments.
This is a replacement spin-on filter element only — it does not include the filter head, mounting bracket, fittings, hoses, or separator assembly.
Compatible Applications
- Volvo Penta SX / EFI gasoline sterndrive applications
- OMC Cobra EFI sterndrive applications
- Compatible fuel/water separator heads with 13/16-18 thread
- Ethanol-blended marine gasoline systems requiring water separation and particulate filtration
- Fuel/water separator assemblies specifying Sierra 18-7789 or a verified OEM equivalent
Confirm the existing filter number, filter-head thread, gasket diameter, and fuel type before ordering. Do not select by engine brand alone.
OEM Cross-Reference Numbers
Volvo Penta:
- 3851218
- 3852413
- 3862228
Johnson / Evinrude / OMC:
- 5009676
- 5011090
- 502906
When to Replace This Filter
- Annual seasonal service or per engine manufacturer’s maintenance schedule
- Water contamination found in the fuel system
- Engine shows signs of fuel restriction: hard starting, rough idle, hesitation, surging, power loss, or stalling under load
- Visible rust, damage, or leaks on the existing canister
- After any contaminated fuel exposure
If significant water is found in the removed filter, inspect the fuel tank and supply before returning the engine to service.
Installation Notes
- Shut off the fuel supply before servicing
- Place absorbent material under the filter before removal
- Confirm the old gasket is not stuck to the filter head — remove it if so
- Clean the sealing surface on the filter head
- Lightly lubricate the new gasket with clean fuel or engine oil
- Install hand-tight per filter instructions — do not overtighten
- Prime the fuel system and check for leaks after startup
- Dispose of used filter and contaminated fuel per local environmental requirements
Technical FAQ
Is 21 micron the same as 20 micron?
No. Sierra rates 18-7789 at 21 micron. Some aftermarket equivalents are marketed at 20 micron. Use the Sierra specification when matching this filter to a service requirement.
Does thread size confirm fitment?
Thread size (13/16-18) is a necessary match but not sufficient on its own. Confirm the OEM cross-reference or existing filter number as well, as similar thread filters can differ in micron rating, gasket diameter, and canister dimensions.
Volvo Penta 3862228 — which engines?
Volvo Penta’s maintenance catalog lists 3862228 across selected 4.3L, 5.0L, 5.7L, 7.4L, and 8.1L gasoline engine families. Confirm by engine model and serial number.
Related Parts
- Volvo Penta 3847644 Fuel Filter / Water Separator – 6 Micron
- Seachoice 50-20938 Fuel/Water Separating Filter – Volvo/OMC – 10 Micron
- Seachoice 50-20937 Fuel/Water Separating Filter – 10 Micron
Parts Desk Insights
The most reliable way to match this filter is by both the OEM filter number and the 13/16-18 filter-head thread. Its strongest verified applications are Volvo Penta SX/EFI and OMC Cobra EFI systems. A common issue is customers ordering by engine brand alone without confirming the filter-head thread or existing part number — this leads to fitment mismatches even on correct engine families. If water is found in the removed filter, always trace it back to the fuel supply before putting the boat back in service.
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.