Mercury Mariner 8HP 4-Stroke Outboard Engine Parts

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This page is dedicated to Mercury/Mariner 4-Stroke 8HP outboard engines. Use it to find compatible parts and practical service information. Below you’ll find maintenance tips, common replacement parts, and troubleshooting guidance. You can also browse the main Mercury collection any time. Scroll to the bottom of this page to start browsing parts for this engine, and remember you can use the Filter & Sort controls on the collection page to narrow results by horsepower, year range, and part category/section.

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How to Identify Your 8HP Model

Locate the serial/nameplate on the transom clamp bracket or swivel bracket. It lists the model designation and serial number.
Model suffixes typically indicate start and shaft options: M = manual start, E = electric, S = 15 in short shaft, L = 20 in long shaft, and remote/tiller control variants.
This is a 4-stroke platform: you’ll see an engine oil fill cap, dipstick, and a cam/valve cover (unlike older 2-strokes).
Many 8HP FourStroke models share components with certain 9.8–9.9HP siblings. Always verify by serial number before ordering.

Engine Overview

Mercury/Mariner 8HP FourStroke

Feature	Description
Configuration	Twin-cylinder, carbureted 4-stroke outboard with manual or electric start and tiller or remote options.
Common Models	8HP FourStroke variants (S/L shaft; manual/electric; tiller/remote). Some share parts with 9.8–9.9HP models.
Advantages	Quiet operation, low fuel consumption, light weight for easy portability, broad parts availability.
Notes	Confirm serial and shaft/start configuration when selecting service parts, propellers, and control components.

Routine Maintenance & Service Parts

Intervals below are general guidelines for a small 4-stroke outboard. Always follow the procedures and schedules in your official service manual.

Item	Interval*	Remarks	Parts Link
Engine oil + filter	First 20 hrs, then every 100 hrs or annually	Warm engine before draining; verify capacity by manual; replace crush washer if equipped.	Mercury Oil Filters
Gear oil (lower unit)	Every 100 hrs or annually	Inspect for water intrusion (milky oil) and metal on the magnetic plug.	Mercury Outboard Parts
Spark plugs	Inspect 100 hrs; replace 200 hrs or as needed	Gap to spec; replace if fouled, worn, or corroded.	Spark Plugs
Fuel filter / inline filter	Inspect 50 hrs; replace annually or with symptoms	Use fresh fuel; add water-separating filtration if rigging allows.	Fuel Filters
Water pump impeller/kit	Inspect annually; replace 2–3 seasons or 200 hrs	Replace sooner if weak tell-tale, overheat alarm, or sand/silt use.	Mercury Water Pump Repair Kits
Anodes (zinc/aluminum/magnesium)	Check every 3 months; replace when ~50% depleted	Choose alloy for your water (salt/brackish/fresh). Keep paint off anodes.	Anodes

*Hours or annual interval, whichever comes first. Shorten intervals for harsh or commercial use.

Frequently Used Parts Categories

Routine Service: Service & Maintenance Kits
Cooling System: Mercury Water Pump Repair Kits
Fuel System: Fuel Filters
Ignition / Electrical: Electrical Items
Gearcase & Seals: Mercury Lower Unit Seal Kits
Propulsion: Propellers
Corrosion Protection: Anodes

Common Symptoms & Quick Checks

Symptom	Check First	Related Parts
Weak tell‑tale stream / overheat alarm	Inspect intake screens for debris; verify hose/tell‑tale is clear; check impeller age; thermostat sticking.	Water pump impeller/kit, thermostat, intake screen, tell‑tale hose.
Hard starting / rough idle	Use fresh fuel; check primer/choke function; inspect inline fuel filter; confirm plug condition and gap.	Fuel filter, carburetor service kit, spark plugs.
Poor acceleration / power loss	Check prop damage or wrong pitch; verify full throttle opening; inspect plugs and fuel supply; look for water in fuel.	Propeller, spark plugs, fuel filter, fuel line components.
Gearcase noise / metal in gear oil	Verify oil level; inspect for milky oil; check prop shaft for fishing line; pressure test seals if contamination found.	Lower unit seal kit, bearings, drain/fill plug seals, gear oil.

FAQs

Are parts interchangeable across different years or between 8HP and 9.9HP models?

Some components are shared among 8–9.9HP FourStroke variants, but not all. Always confirm with your serial number, shaft length, and start/control type before ordering.

When should I replace the water pump impeller?

Inspect annually and replace every 2–3 seasons (or about 200 hours). Replace sooner if you notice a weak tell‑tale, overheat warnings, or frequent operation in sandy or silty water.

How often should I change lower unit gear oil?

Every 100 hours or once a season. Check sooner if you strike an object, see leaks, or find milky oil indicating water intrusion.

What information helps confirm part compatibility?

Provide the engine serial number, model designation, shaft length (S/L), start type (manual/electric), and whether it’s tiller or remote control. A clear photo of the nameplate also helps.

Ready to find parts by horsepower, year, and model? Start in the main Mercury collection and filter to your exact 8HP FourStroke.

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If you’re unsure about your model, send us a photo of the nameplate and the part you need and we’ll help verify compatibility.