MerCruiser 4-Stroke 220-377HP Marine Engine

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This page supports MerCruiser 4-Stroke 220–377 HP sterndrive/inboard 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 MerCruiser collection. Scroll to the bottom of this page to start browsing parts for this engine, and remember you can use the Filter & Sort controls on collection pages to narrow results by horsepower, year range, and part category.

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How to Identify Your 220–377 HP Model

Serial/ID plate: Typically on the flame arrestor cover or starboard side of the engine block. For the drive, check the transom assembly tag (starboard side) and the drive unit sticker.
Model wording: Look for family names such as 4.3L, 5.0L, 350 MAG/MPI, 6.2L, or 8.2 MAG. Suffixes may indicate fuel system (MPI/EFI), digital controls (DTS), or emissions variants.
Drive family: Identify Alpha vs. Bravo (I/II/III). Many parts are drive-specific (bellows, gear lube capacity, prop/hub hardware).
Platform cues: V6 (4.3L) vs. V8 (5.0/5.7/6.2/8.2). V8s have two cylinder banks and generally higher output; some service items differ by platform.

Platform Overview

V6 4.3L (approx. 220–225 HP)

Feature	Description
Configuration	V6 4-stroke gasoline; carbureted or EFI/MPI; typically paired with Alpha or Bravo drives.
Common Models	4.3L, 4.3LX, 4.3 MPI
Advantages	Compact package, solid mid-range torque, good efficiency for runabouts and cruisers.
Notes	Impeller type and fuel filtration can vary by year and cooling layout; confirm by serial and drive family.

Small-Block V8 (5.0L / 5.7L / 6.2L) — approx. 260–350 HP

Feature	Description
Configuration	V8 4-stroke gasoline; carb or MPI/EFI; commonly Alpha/Bravo; includes popular 350 MAG and 6.2L families.
Common Models	5.0L, 5.7L/350 MAG MPI, 6.2L 300/350
Advantages	Broader powerband and stronger top-end; wide parts availability.
Notes	Some exhaust, belt, and sensor components differ between generations; verify by serial number.

Big-Block V8 (8.2L MAG/Horizon) — approx. 370–377 HP

Feature	Description
Configuration	V8 4-stroke gasoline; typically Bravo drives; robust cooling and exhaust components.
Common Models	8.2 MAG, 8.2L Horizon
Advantages	High torque for heavy boats; strong cruise and WOT performance.
Notes	Use correct big-block impeller kit, belt routing, and anode sets; many parts are big-block specific.

Routine Maintenance & Service Parts

Intervals below are general guidelines for MerCruiser 4-stroke sterndrive/inboard engines. Always follow the official service manual for your exact model and usage.

Item	Interval*	Remarks	Parts Link
Engine oil + filter	100 hours or annually	Use marine-rated oil; warm engine before draining for a complete change.	MerCruiser Service & Maintenance Kits
Spark plugs	100 hours or annually	Check gap; replace sooner if fouled or misfire occurs.	Spark plug
Fuel filter / water separator	100 hours or annually	Drain bowl and inspect for water; replace filter element routinely.	MerCruiser Fuel Filters
Raw water pump impeller	2 seasons or 200 hours (sooner in sandy/silty water)	Replace at first sign of weak telltale or rising temps.	MerCruiser Impellers
Thermostat	Every 2–3 seasons	Replace if overcooling/overheating or unstable temps are observed.	MerCruiser
Sterndrive gear oil (Alpha/Bravo)	100 hours or annually	Inspect magnet for metal; change sooner if water intrusion is present.	MerCruiser Service & Maintenance Kits
Anodes (engine & drive)	Inspect every 50 hours; replace when 50% depleted	Match anode material (zinc/aluminum/magnesium) to your water type.	MerCruiser Anodes
Serpentine/V-belt	Inspect 100 hours; replace 2–3 seasons or on cracks/glazing	Tension and alignment affect alternator and raw-water pump performance.	Belt

Frequently Used Parts Categories

Routine Service — MerCruiser Service & Maintenance Kits
Cooling System — MerCruiser Impellers
Fuel System — MerCruiser Fuel Filters
Ignition / Electrical — Starters
Exhaust & Gaskets — Manifolds
Corrosion Protection — MerCruiser Anodes
Propellers & Hardware — MerCruiser Propellers

Common Symptoms & Quick Checks

Symptom	Check First	Related Parts
Weak water stream or overheat alarm	Inspect sea inlet screens, hoses, and belt; confirm impeller age; verify thermostat action.	Raw water pump impeller kit, pump housing, thermostat, intake screen, hoses/clamps.
Hard starting or rough idle	Check battery voltage and grounds; inspect/replace fuel filter; verify plug condition and gap; look for vacuum leaks.	Spark plugs, fuel filter/water separator, ignition components, intake gaskets.
Poor acceleration or power loss	Confirm clean prop; check for fuel restriction; scan for misfire; verify throttle/shift linkages.	Propeller, fuel filter, fuel pump, spark plugs/ignition parts, sensors.
Milky or metal-laden gear oil	Inspect drain/fill seals and shift shaft/prop shaft seals; pressure/vacuum test the drive.	Gear lube, seal kits, prop shaft seals, drain/fill gaskets.
Trim/tilt inoperative	Check fuses/relays, battery voltage, and fluid level; listen for trim motor operation; inspect switch and wiring.	Trim motor, relays, switches, hydraulic fluid and hoses.

FAQs

Are parts interchangeable between different years or platforms?

Some items carry over, but many parts differ between V6/V8 families and Alpha vs. Bravo drives. Use the engine and drive serial numbers to verify exact compatibility before ordering.

When should the raw-water impeller be replaced?

As a rule, every 2 seasons or ~200 hours—earlier if you operate in sandy or silty water or see reduced water flow or rising temperatures.

How often should sterndrive gear oil be changed?

Every 100 hours or annually. If the oil appears milky or you find water during draining, service immediately and pressure-test the drive to locate leaking seals.

What information do you need to confirm part compatibility?

Please provide the engine serial number, drive family (Alpha/Bravo), model designation (e.g., 4.3L, 350 MAG, 6.2L, 8.2 MAG), and boat year. Photos of the nameplate and the part to be replaced also help.

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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.