Mercury 325HP 4-Stroke Outboard Engine Parts

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This page focuses on Mercury 4-Stroke 325HP outboard engines and helps you find compatible parts and service information. Below you’ll find maintenance tips, commonly replaced parts, and troubleshooting guidance. You can also browse the main Mercury collection. Scroll to the bottom of this 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.

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How to Identify Your 325HP Model

Locate the serial number plate on the transom bracket or swivel bracket. Record the full serial/number string and any model suffixes.
Decode the model tag: suffixes may indicate shaft length, control type (mechanical vs DTS), and market/year. This is essential for selecting correct gearcase and cooling parts.
Confirm platform: many high-output Mercury 4-strokes are either supercharged inline‑6 (Verado L6) or later large-frame V8/V10 platforms. Cowling shape, steering/power steering modules, and intake layout help distinguish them.
Note rigging: Digital Throttle & Shift (DTS) vs mechanical controls, and power steering presence, can affect certain service and rigging components.

Platform Overview

Supercharged Inline‑6 Verado (L6)

Feature	Description
Configuration	Supercharged inline‑6 EFI 4‑stroke with integrated electro‑hydraulic steering on many models.
Common Models	Often aligned with Verado L6 high‑output ranges (e.g., 300–350 HP). Some service parts may overlap across adjacent HP ratings; always match by serial number.
Advantages	Strong mid‑range torque, smooth operation, and refined NVH characteristics.
Notes	Gearcase options (standard vs heavy‑duty), thermostat spec, and anode sets can vary. Verify cooling and gearcase parts by serial prefix and gear housing size.

Large‑Frame V8/V10 4‑Stroke (Verado / Pro XS Families)

Feature	Description
Configuration	Naturally aspirated, large‑displacement EFI 4‑stroke (V8 or V10, platform dependent) with advanced charging and digital controls on many variants.
Common Models	High‑output 4‑stroke families in the 300–400 HP range. A 325 HP calibration may share many service items with adjacent outputs; confirm by serial.
Advantages	Broad torque curve, robust charging for electronics, and strong mid‑to‑top‑end performance.
Notes	Water pump kits, anodes, and gearcase seals may differ by gearcase diameter and shaft length. DTS vs mechanical control components are not interchangeable.

Routine Maintenance & Service Parts

Service intervals below are general guidelines for high‑horsepower Mercury 4‑stroke outboards. Always follow the official service manual for your exact serial number and operating conditions.

Item	Interval*	Remarks	Parts Link
Engine oil + filter	100 hours or annually	Use marine FC‑W oil grade specified in your manual; replace filter and drain plug seals at each oil change.	Shop Oil Filters
Gear oil (lower unit)	100 hours or annually	Inspect magnet for metal, replace drain screw gaskets, and pressure/vac test if water is present.	Lower Unit Seal Kits
Spark plugs	300 hours or 3 years	Check gap and heat range per platform; boosted engines can be sensitive to plug condition.	Shop Spark Plugs
Fuel filter / water separator	100 hours or each season	Replace engine‑mounted and boat‑mounted filters; monitor for water and debris.	Shop Fuel Filters
Water pump impeller / kit	200 hours or 2 seasons (sooner in sandy/silty water)	Replace if tell‑tale weak, temps elevated, or after an overheat/over‑rev in shallow water.	Mercury Water Pump Kits
Anodes (internal & external)	Inspect every 50 hours; replace at ~50% wear	Match anode alloy to your water (zinc–salt, aluminum–brackish, magnesium–fresh) and keep electrical bonding intact.	Shop Anodes

*Intervals are typical for recreational duty. Severe use (commercial, trolling, high hours, sandy water) may require shorter intervals.

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	Inspect intake screens for debris, verify impeller condition, and test thermostats; confirm proper anode condition.	Water pump kit, thermostat(s), intake screen, anodes
Hard starting or rough idle	Charge/test battery, check spark plugs, confirm clean fuel and replace filters; inspect for air leaks on fuel lines.	Spark plugs, inline fuel filter, water‑separating filter
Poor acceleration or power loss	Inspect propeller for damage or wrong pitch, check for fuel restriction, verify plug and coil condition.	Propeller/hub, fuel filter, fuel pump, spark plugs
Gearcase noise or metal in gear oil	Check oil level/condition, look for water intrusion, inspect propshaft seals for fishing line, and perform pressure/vac test.	Drain plug seals, lower unit seal kit, bearings

FAQs

Are parts interchangeable across different years or platforms?

Some service items overlap across adjacent horsepower ratings and years, but many components differ by serial prefix, gearcase type, control system (DTS vs mechanical), and platform (L6 vs V8/V10). Always match parts to your exact serial number.

When should the water pump impeller be replaced?

Common practice is every 200 hours or two seasons, and sooner for sandy/silty use. Replace immediately after any overheat event or if the tell‑tale stream weakens.

How often should I change lower unit gear oil?

At least every 100 hours or annually. If you detect water, metal debris, or burned odor, service the gearcase sooner and consider a seal kit with pressure/vacuum testing.

What information do I need to confirm part compatibility?

Provide the engine serial number, model name, horsepower, shaft length, control type (DTS or mechanical), gearcase size, and country/market. Photos of the nameplate and the part needed are also helpful.

Ready to find the parts you need? Browse the Mercury collection by horsepower, year, and model to narrow down compatible components for your engine.

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