MerCruiser 377HP 4-Stroke Marine Engine Parts

(1 products)

This page is tailored for MerCruiser 4‑Stroke 377HP sterndrive/inboard 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 MerCruiser collection for a wider selection. Scroll to the bottom of this page to start browsing parts for this engine, and remember that on the collection page you can use the Filter & Sort controls to narrow results by horsepower, year range, and part category.

Browse All MerCruiser Parts

How to Identify Your 377HP Model

Locate the engine serial/ID label: commonly on the starboard side of the engine near the flywheel housing, on a valve cover tag, or on a decal near the flame arrestor/ECM cover.
Drive serial plate: look on the outdrive’s identification tag (gimbal area or drive housing) to confirm Alpha vs Bravo family and ratio.
Model codes and suffixes: terms like “377 MAG/MPI,” “HO,” or “Catalyst/Non‑Catalyst” indicate fuel system and emissions package; they affect parts such as exhaust, sensors, and service kits.
Cooling/impeller location: Alpha packages typically use an impeller in the lower unit; Bravo packages generally use an engine‑mounted sea water pump—this changes which impeller kit you need.

Engine Overview

MerCruiser 377HP Platform

Feature	Description
Configuration	6.2L small‑block V8, multi‑port EFI, 4‑Stroke marine long block; typically paired with Alpha or Bravo sterndrives.
Common Models	Examples include 6.2L V8 packages around 377 HP (e.g., 377 MAG/MPI variants) used in sterndrive and inboard applications.
Advantages	Strong mid‑range torque, smooth EFI drivability, broad parts availability, and robust cooling/exhaust options for varied duty cycles.
Notes	Confirm raw‑water vs closed‑cooling setup; Alpha vs Bravo impeller location differs; use engine and drive serial numbers to ensure exact parts compatibility.

Routine Maintenance & Service Parts

Intervals below are general guidelines; always follow the official MerCruiser service manual for your specific serial number and operating conditions.

Item	Interval*	Remarks	Parts Link
Engine oil + filter	100 hours or annually	Use FC‑W compliant marine oil; replace filter every oil change.	MerCruiser Oil Filters
Gear oil (sterndrive)	100 hours or annually	Check for water intrusion and metal; service sooner after heavy use or storage.	MerCruiser Service & Maintenance Kits
Spark plugs	200–300 hours or 3 years	Replace sooner if misfire, fouling, or hard starts occur.	Spark Plug
Fuel filter / water separator	100 hours or annually	Drain/replace more often in humid or ethanol‑blend environments.	MerCruiser Fuel Filters
Water pump impeller / kit	2 seasons or 200 hours	Alpha: impeller in drive; Bravo: engine‑mounted sea pump—order accordingly.	MerCruiser Impellers
Anodes (zinc/aluminum/magnesium)	Inspect every 50 hours; replace at ~50% loss	Match alloy to water type (salt, brackish, fresh) and keep electrical system grounded.	MerCruiser Anodes
Serpentine/accessory belt	Inspect every 100 hours; replace as needed	Replace if cracked, glazed, or noisy; verify tensioner condition.	Belt

Frequently Used Parts Categories

Routine Service: MerCruiser Service & Maintenance Kits
Oil & Filtration: MerCruiser Oil Filters
Cooling System: MerCruiser Impellers
Fuel System: MerCruiser Fuel Filters
Ignition / Electrical: Electrical Items
Corrosion Protection: MerCruiser Anodes
Propulsion: Propellers

Common Symptoms & Quick Checks

Symptom	Check First	Related Parts
Weak water stream or overheat alarm	Inspect intake screens/sea strainer, impeller condition, and thermostat; verify hose clamps and leaks.	Water pump impeller kit, thermostat, intake screens/hoses
Poor acceleration or power loss	Check fuel quality, water separator, spark plugs, and prop condition/pitch; scan for EFI fault codes.	Fuel filter/water separator, spark plugs, propeller
Hard starting or rough idle	Verify battery voltage and grounds, inspect plugs and ignition leads, check for vacuum leaks and stale fuel.	Spark plugs, electrical connectors, fuel filter
Gearcase noise or metal in gear oil	Confirm oil level/condition, check for milky oil (water intrusion), inspect propshaft seals and prop hub.	Lower unit seal kit, prop hardware, gear lube service kit

FAQs

Are parts interchangeable between different years or platforms?

Some service items cross over, but many components (cooling, exhaust, sensors, and ignition) vary by serial number, emissions package, and drive family. Always verify with your engine and drive serials.

When should I replace the impeller?

As a preventive measure every 2 seasons or about 200 hours, sooner if you see overheat warnings, weak flow, or debris damage. Alpha vs Bravo setups use different impeller/sea pump kits.

How often should gear oil be changed?

Typically every 100 hours or annually, and after any prop‑striking incident or extended storage. Replace seals if water intrusion is detected.

What information do you need to confirm part compatibility?

Provide engine serial number, drive serial number (Alpha/Bravo and ratio), cooling type (raw vs closed), and any model suffixes (e.g., MPI, Catalyst). Photos of the nameplate help ensure exact matches.

Ready to find parts by horsepower, year, and model? Browse the main MerCruiser collection to dial in compatible components for your 377HP package.

Shop MerCruiser 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.