Mercury Quicksilver OEM Inline Fuel Filter 879885K | 35-879885K | EFI FourStroke & Verado Outboard

Mercury Quicksilver OEM Inline Fuel Filter — Part 879885K

• Part Number: 879885K
• Full Catalog Number: 35-879885K
• Brand: Mercury Marine / Quicksilver (Genuine OEM)
• Official Product Type: Fuel System Parts — Under-Cowl Inline Fuel Filter
• Filter Type: Inline, under-cowl — connects directly into the fuel line beneath the engine cowl (not a bowl-style element or screw-in cartridge)
• Fuel Line Connection: Approx. 8 mm / 5⁄8-inch inline
• System: EFI / high-pressure outboard fuel delivery
• Application: Selected Mercury FourStroke EFI and Verado outboards, 30–400 HP, where 879885K is specified in the fuel-system diagram
• GTIN / UPC: 745061813182
• Weight: approx. 0.1 kg

Inline filter — confirm style and serial number before ordering: 879885K is the under-cowl inline fuel filter for EFI FourStroke and Verado applications — it connects directly into the fuel line with barb or push-connect fittings. It is not the bowl-style filter element (35-87946Q04) used on carbureted Mercury outboards, nor a screw-in cartridge. The same horsepower family can use different under-cowl filter arrangements depending on production range and fuel-system configuration. Confirm 879885K against the serial-number-specific Mercury fuel-system diagram before ordering.

What It Is

The 879885K / 35-879885K is the genuine OEM under-cowl inline fuel filter for applicable Mercury FourStroke EFI and Verado outboards. Installed directly in the fuel supply line beneath the engine cowl, it captures particles and debris before fuel reaches the high-pressure EFI system — protecting fuel injectors, the high-pressure fuel pump, and downstream fuel-delivery components. Replacing it on schedule is one of the most cost-effective ways to maintain reliable EFI performance and protect against injector contamination. Mercury’s current application data covers selected 30–400 HP FourStroke EFI and Verado models where 879885K is specified in the fuel-system diagram.

Compatible Applications

Confirm fitment by engine serial number and the Mercury fuel-system diagram before ordering. The same horsepower family may use different fuel filter configurations depending on production range.

• Mercury FourStroke EFI 30 / 40 HP — 3-cylinder — where the Mercury diagram specifies 879885K by serial number
• Mercury FourStroke EFI 40 / 50 / 60 HP — 996 cc 4-cylinder — where specified by serial number
• Mercury FourStroke 75–115 HP 1.7L — serial range 1B366823–2B094995 — where specified
• Mercury FourStroke 75–115 HP 2.1L — serial 2B094996 and above — where specified
• Mercury FourStroke EFI 150 HP — serial 1B905505 and above — where specified
• Mercury Verado L4 (135–200 HP range) — where specified by serial number
• Mercury Verado L6 (200–400 HP range) — where specified by serial number

Not sure it fits? Send us your Mercury outboard serial number before ordering.

Part Numbers & Cross-References

• 879885K — Mercury OEM part number
• 35-879885K — Full Mercury / Quicksilver catalog number
• 879885Q / 35-879885Q — Related Quicksilver-branded inline filter reference (verify by application)
• 879885T / 35-879885T — Earlier related reference (verify by application)
• Sierra 18-7718 — Aftermarket cross-reference for the 879885 filter family (verify by serial number and diagram)

Related Fuel System Parts

• Mercury Quicksilver Under-Cowl Fuel Filter Kit 35-87946Q04 — Bowl-Style Element | 6–60 HP 2-Stroke Outboard
• Mercury Quicksilver Fuel Filter 802893Q01
• Mercury MerCruiser Fuel Filter Kit 8M0088825
• Mercury MerCruiser Fuel Filter 8M0090809
• Mercury MerCruiser Fuel Filter Kit 8M0106635
• Mercury Quicksilver Fuel Pump Kit 892267A51

When to Replace

Replace the inline fuel filter when:

• Annual fuel-system maintenance is due
• The 100-hour service interval has been reached
• Fuel contamination or debris is found in the system
• EFI fuel-system service or fuel injector service is being performed
• The engine shows hard starting, hesitation, lean running, or fuel starvation symptoms
• Stale fuel, ethanol-related debris, or tank contamination has entered the fuel circuit
• The original filter is physically damaged or aged

Note: restricted fuel flow can contribute to hard starting and hesitation, but these symptoms can also result from fuel pump, injector, or pressure-regulation issues. A filter replacement is a logical first step before diagnosing more expensive components.

Service Interval

Replace annually or at every 100-hour service, whichever comes first. On high-pressure EFI systems, a clogged or bypassed fuel filter can cause injector damage that is significantly more expensive than the cost of a routine filter replacement. In boats using ethanol-blend fuel, more frequent inspection is recommended — ethanol can accelerate debris accumulation at the filter from fuel tank linings and hose degradation.

Installation Notes

• Relieve fuel system pressure before disconnecting the filter on EFI engines — follow the Mercury service manual depressurization procedure for the specific engine model before removing any EFI fuel line
• Note the flow direction arrow on the filter body before removal — install the replacement in the same orientation
• Inspect the adjoining fuel hoses and connections for cracking, softening, or connector wear before reinstalling
• Ensure both inline connections are fully seated and secure before starting the engine
• Prime the fuel system as required after installation
• Inspect carefully for fuel leaks at both filter connections before running the engine

Technical FAQ

Q: How is 879885K different from the bowl-style under-cowl filter (35-87946Q04)?
879885K is an inline filter — it connects directly into the fuel line with barb or push-connect fittings. The 35-87946Q04 is a bowl-style cartridge element that sits inside a reusable housing and is serviced by removing the bowl. They are not interchangeable. Confirm which style your engine uses by checking the fuel-system diagram for your serial number.

Q: Does this filter fit both carbureted and EFI outboards?
879885K is designed for EFI and high-pressure fuel systems. Carbureted outboards and older 2-stroke Mercury outboards typically use a different filter style (such as the bowl-style 35-87946Q04 or an inline barb filter). Confirm by serial number and fuel-system diagram.

Q: What is the difference between 879885K, 879885Q, and 879885T?
879885Q and 879885T are related Quicksilver-branded and earlier references in the same 879885 filter family. 879885K is the current stocking number. Confirm which suffix your Mercury fuel-system diagram specifies for the exact engine model and serial number, or contact us with your serial number for verification.

Q: Why do I need to depressurize the EFI fuel system before removing this filter?
EFI fuel systems operate at high pressure (typically 35–60+ PSI depending on the engine). Disconnecting an EFI fuel line without first relieving the pressure can result in pressurized fuel spray, which is a fire and safety hazard. Always follow the Mercury service manual depressurization procedure for the specific engine before disconnecting any EFI fuel line connection.

Parts Desk Insights

The most important distinction with 879885K is the filter style — it is the inline under-cowl filter, not the bowl-style element and not the screw-in cartridge used on some other fuel systems. Customers ordering a fuel filter for a Mercury FourStroke or Verado sometimes receive the wrong style because they search by horsepower rather than confirming the filter configuration under the cowl. Confirming the style before ordering prevents the most common return situation. The depressurization step before EFI filter removal is also worth flagging for customers doing this service themselves — it is easy to overlook and can result in pressurized fuel spray. Annual replacement paired with spark plugs and gear oil is the right recommendation for any EFI FourStroke or Verado outboard.