Mercury 4-Stroke Outboard Engine 15-50HP Parts

(2 products)

This page supports Mercury 4‑Stroke 15–50HP outboard engines. Use it to find compatible parts and service information, including maintenance tips, common replacement parts, and troubleshooting guidance. You can also browse the main Mercury collection. Scroll to the bottom of the page to start browsing parts for this engine. On the collection page, use the Filter & Sort controls to narrow results by horsepower, year range, and part category/section.

Browse All Mercury Parts

How to Identify Your 15–50HP Model

Locate the serial/nameplate on the swivel bracket (port/starboard side) or near the clamp/steering tube. The top line is the serial number; a secondary stamp may indicate year.
Model codes and suffixes indicate features such as shaft length (S/L/XL), start type (manual/electric), control type (tiller/remote), and gearcase option (standard vs BigFoot).
Platform clues: 15–20HP are typically inline‑2 four‑strokes; 25–50HP are commonly inline‑3 four‑strokes. Many 40–50HP units use EFI; some earlier/smaller models may be carbureted.
BigFoot (Command Thrust) models have a larger gearcase and propeller for better thrust. Verify this before ordering propellers, gearcase seals, or water pump kits.

Platform Overview

15–20HP FourStroke (Portable)

Feature	Description
Configuration	Inline‑2 four‑stroke, manual or electric start, tiller or remote options.
Common Models	Mercury 15HP and 20HP FourStroke portable models (short/long shaft variants).
Advantages	Lightweight, quiet operation, excellent trolling economy.
Notes	Confirm pull‑start vs electric‑start parts, and shaft length before ordering controls, cables, or propellers.

25–30HP FourStroke (Midrange)

Feature	Description
Configuration	Inline‑3 four‑stroke, carbureted or EFI depending on year; remote or tiller.
Common Models	Mercury 25HP and 30HP FourStroke models; many parts shared across the two outputs.
Advantages	Strong mid‑range torque, smooth operation, broad parts availability.
Notes	EFI units require specific high‑pressure fuel filters; verify EFI vs carb before ordering fuel components.

40–50HP FourStroke (EFI/BigFoot Options)

Feature	Description
Configuration	Inline‑3 EFI four‑stroke on most later models; BigFoot/Command Thrust gearcase available for heavy loads.
Common Models	Mercury 40HP and 50HP FourStroke (standard and BigFoot). Many 50HP engines are EFI.
Advantages	Good fuel economy, reliable EFI starting, strong thrust with BigFoot for pontoons and workboats.
Notes	Propellers, gear ratios, and water pump kits can differ between standard and BigFoot gearcases—confirm before purchase.

Routine Maintenance & Service Parts

Intervals below are general guidelines for Mercury four‑stroke outboards in the 15–50HP class. Always follow the service schedule and specifications in your official Mercury manual for your exact serial range.

Item	Interval*	Remarks	Parts Link
Engine oil & filter	Every 100 hours or annually (after break‑in)	Warm engine before draining; replace crush washer; verify oil weight per manual.	Oil Filters
Gear oil (lower unit)	Every 100 hours or annually	Inspect for water intrusion (milky oil) and metal; replace drain/fill gaskets.	Mercury Lower Unit Seal Kits
Spark plugs	Inspect 100 hours; replace 200–300 hours or as needed	Check gap and insulator color; misfire under load often indicates worn plugs.	Spark Plugs
Fuel filter / water‑separating filter	Inspect every 50–100 hours; replace annually	EFI models require the correct high‑pressure filter; replace bowl gaskets if equipped.	Fuel Filters
Water pump impeller / kit	Every 2–3 seasons or 200 hours (inspect annually)	Essential for cooling; more frequent service for sandy/silty use or weak tell‑tale.	Mercury Water Pump Repair Kits
Anodes (zinc/aluminum/magnesium)	Inspect every 50 hours; replace when 50% consumed	Choose alloy for your water type (salt/brackish/fresh). Keep paint off anodes.	Anodes

Frequently Used Parts Categories

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

Common Symptoms & Quick Checks

Symptom	Check First	Related Parts
Weak tell‑tale or overheat alarm	Clear intake screens; inspect tell‑tale hose; verify impeller condition and thermostat operation.	Water pump repair kit, intake screen, thermostat, gaskets
Poor acceleration / power loss	Check prop damage/cavitation; replace fuel filter; verify fresh plugs; confirm throttle opening and EFI sensors.	Propeller, fuel filter, spark plugs, air/fuel filters, EFI components
Hard starting / rough idle	Prime fuel system; confirm clean fuel; test plugs; inspect IAC/idle system (EFI) and vacuum leaks.	Spark plugs, fuel filter, injectors (EFI), intake gaskets, primer bulb
Charging system not working	Measure battery voltage; check fuses and connections; test rectifier/regulator output.	Rectifier/regulator, wiring, battery leads, fuses
Gearcase noise or metal in gear oil	Drain and inspect oil; look for water intrusion; check prop shaft seal and drain/fill plug gaskets.	Lower unit seal kit, bearings, drain/fill gaskets

FAQs

Are parts interchangeable across different years or BigFoot vs standard models?

Some components interchange within the same platform and serial range, but key items (propellers, gearcase seals, water pump kits) can differ between standard and BigFoot gearcases and across EFI/carb model years. Verify by serial number and model suffix 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 operate in sandy/silty water, see a weak tell‑tale, or after an overheat event.

How often should I change lower‑unit gear oil?

Change every 100 hours or annually, and any time you observe water contamination or metal particles. Always replace drain/fill plug gaskets.

What information do you need to confirm part compatibility?

Please provide the engine serial number, model code/suffix (shaft length, tiller/remote, BigFoot/standard), approximate year, and whether the engine is EFI or carbureted.

Ready to find parts for your Mercury FourStroke 15–50HP? Browse the main Mercury collection by horsepower, year, and model to quickly locate compatible components.

Shop Mercury Outboard Parts

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.