{"product_id":"sierra-fuel-filter-18-7844-short-21-micron-spin-on-90-gph-flow-mercury-cross-reference","title":"Sierra Fuel Filter 18-7844 (Short) 21‑Micron Spin‑On — 90 GPH Flow, Mercury Cross‑Reference","description":"\u003cb\u003eThe Sierra 18-7844 fuel filter is a short, 21-micron replacement filter engineered to remove fine particulates and water from gasoline blends while maintaining a 90 GPH flow for high-demand outboard engines.\u003c\/b\u003e\n\n\u003cp\u003eThis compact spin-on fuel filter from Sierra is built as a direct-fit replacement for Mercury Marine part numbers 35-807172 and 35-802893Q. With a 21-micron media rating and a design that supports a steady 90 gallons-per-hour flow, it balances filtration efficiency with the fuel delivery needs of larger or high-revving marine engines. The element also helps manage contaminants introduced by ethanol-blended fuels that can loosen deposits and absorb moisture.\u003c\/p\u003e\n\n\u003ch3\u003eHow does this filter protect my outboard engine?\u003c\/h3\u003e\n\u003cp\u003eThe 21-micron element traps fine particles that could abrade internal fuel system components and clog injectors or carburetors. It also reduces the amount of water and debris reaching the pump and motor, helping maintain consistent combustion and performance.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003e21-micron media captures small particulates without starving fuel flow\u003c\/li\u003e\n  \u003cli\u003eDesigned to handle ethanol-blended gasoline contaminants\u003c\/li\u003e\n  \u003cli\u003eMaintains clean fuel to protect pumps, injectors, and carburetors\u003c\/li\u003e\n  \u003cli\u003eSpin-on design simplifies replacement during routine maintenance\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eWill it fit my Mercury engine and how do I identify compatibility?\u003c\/h3\u003e\n\u003cp\u003eSierra 18-7844 is made to replace Mercury OEM 35-807172 and 35-802893Q, matching thread and physical dimensions for a direct swap in compatible models. Check your current filter’s part number or consult your engine’s parts manual to confirm fit before purchasing.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eOEM cross-reference: Mercury Marine 35-807172\u003c\/li\u003e\n  \u003cli\u003eThread pitch specification included for fit verification (42690)\u003c\/li\u003e\n  \u003cli\u003eShort size form factor: listed as Short - 3875\" \/ 984mm for space-limited mounts\u003c\/li\u003e\n  \u003cli\u003eDesigned to meet factory flow and filtration needs for applicable engines\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eHow does it perform with ethanol-blended fuels?\u003c\/h3\u003e\n\u003cp\u003eEthanol in modern fuels tends to absorb water and loosen varnish and deposits; this filter’s media is sized to trap those loosened particles and separate some free water before it reaches the engine. Regular replacement helps avoid filter clogging and fuel delivery interruptions caused by ethanol-related contaminants.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eMedia captures varnish and debris released by ethanol blends\u003c\/li\u003e\n  \u003cli\u003eHelps limit water carry-over into the fuel system\u003c\/li\u003e\n  \u003cli\u003eRecommended regular change intervals prevent flow restriction\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eWhat flow and service expectations should I plan for?\u003c\/h3\u003e\n\u003cp\u003eThe filter is rated to flow at 90 GPH, which supports even high-demand motors while providing fine filtration. Service interval depends on fuel quality and engine hours; inspect during scheduled maintenance and replace when flow or contamination indicates reduced effectiveness.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eRated flow: 90 gallons per hour to support high-demand engines\u003c\/li\u003e\n  \u003cli\u003eFilter efficiency: 21-micron rating for fine particulate removal\u003c\/li\u003e\n  \u003cli\u003eInspect at regular intervals; replace when clogged or per manufacturer schedule\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eWho is this for: The Sierra 18-7844 is aimed at boat owners and marine technicians who operate Mercury-compatible outboards and need a compact, high-flow fuel filter that balances fine-particle filtration with steady fuel delivery. It’s especially beneficial for vessels that run on ethanol-blended gasoline or that require a short-style filter to fit tight mounting locations. Use it when you need a direct-replacement element to maintain factory-level performance and protect fuel-system components.\u003c\/p\u003e\n\u003csection class=\"product-faq-snippet\"\u003e\u003ch3\u003eFAQ\u003c\/h3\u003e\n\u003cdiv class=\"faq-item\"\u003e\n\u003cp class=\"faq-q\"\u003eQ: Is the Sierra 18-7844 a direct replacement for Mercury 35-807172?\u003c\/p\u003e\n\u003cp class=\"faq-a\"\u003eA: Yes. The Sierra 18-7844 cross-references Mercury Marine 35-807172 and 35-802893Q for direct fitment.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"faq-item\"\u003e\n\u003cp class=\"faq-q\"\u003eQ: What micron rating and flow does this filter provide?\u003c\/p\u003e\n\u003cp class=\"faq-a\"\u003eA: It uses a 21-micron element and is rated to flow 90 gallons per hour for high-demand engines.\u003c\/p\u003e\n\u003c\/div\u003e\u003c\/section\u003e","brand":"Sierra","offers":[{"title":"Default Title","offer_id":55164094873943,"sku":"B0001CLG2S","price":33.33,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1050\/1524\/7191\/files\/sierra-18-7844-front-view.jpg?v=1790350101","url":"https:\/\/britishgarage.co.uk\/products\/sierra-fuel-filter-18-7844-short-21-micron-spin-on-90-gph-flow-mercury-cross-reference","provider":"British Garage","version":"1.0","type":"link"}