Indmar 4-Stroke 320HP Marine Engine Parts

(5 products)

This page is built for Indmar 4‑Stroke 320 HP inboard gasoline engines. Use it to find compatible replacement parts, routine service guidance, and quick troubleshooting tips. You can also browse our MerCruiser collection for many crossover inboard service items used on GM‑based Indmar engines. Scroll to the bottom to start browsing parts for this engine, and remember: on the collection pages you can use the Filter & Sort controls to narrow results by horsepower, year range, and part category.

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How to Identify Your 320 HP Model

Find the Indmar serial/nameplate: commonly stamped on the engine block and shown on adhesive tags on major components. Record the full six‑digit serial.
Look for the engine family badge on the flame arrestor or rocker cover (for example: Assault, RTP, Monsoon, MCX/LQ9, 6.0 PFI). These indicate displacement and fuel system.
Confirm fuel and cooling type: most 320 HP units are multi‑port fuel injected (PFI). Cooling may be raw‑water (open) or closed (heat exchanger with propylene glycol).
Note transmission and V‑drive details (ZF Hurth, Walters, or Ski‑Vee) — service fluids and coolers differ by model and affect parts selection.

Engine Platform Overview

Indmar Small‑Block V8 PFI (5.7 L)

Feature	Description
Configuration	GM‑based 5.7 L V8, 4‑stroke, multi‑port fuel injection (PFI); raw‑water or closed‑cooling options.
Common Models	Examples include Assault 325 PFI, RTP‑1 PFI, and Malibu Monsoon variants around 320–340 HP.
Advantages	Broad torque for tow‑sports, reliable EFI starts, wide parts availability, and straightforward maintenance.
Notes	Typical thermostat ~160°F; Indmar recommends 15W‑40 marine oil for most small‑blocks; replace raw‑water pump impeller routinely; observe first 10–20 hr break‑in service.

Indmar Small‑Block V8 PFI (6.0 L)

Feature	Description
Configuration	GM‑based 6.0 L V8, 4‑stroke, PFI; often paired with ZF Hurth/Walters drive options; raw‑water or closed cooling.
Common Models	Examples include Indmar 6.0 PFI and MasterCraft LQ9‑equipped packages near the 320 HP class.
Advantages	Higher mid‑range output for heavy ballast or elevation, strong towing characteristics, EFI drivability.
Notes	Follow first 10–20 hr service, then 50 hr/annual intervals; consider premium octane if specified; maintain heat‑exchanger zincs on closed‑cooling systems.

Routine Maintenance & Service Parts

Intervals below are common guidelines for Indmar small‑block V8s. Always prioritize your official Indmar operator’s manual for exact procedures, fluids, and schedules.

Item	Interval*	Remarks	Parts Link
Engine oil & filter	First 10–20 hrs, then every 50 hrs or annually	Most small‑blocks use 15W‑40 marine oil; replace filter at each service.	Oil Filters
Transmission/V‑drive fluid	First 10–20 hrs, then annually	Fluid type depends on ZF Hurth vs. Walters; inspect cooler and screen.	MerCruiser
Raw‑water pump impeller	Inspect every season; replace 1–2 seasons or sooner if sandy/silty	Overheating often traces to a worn or run‑dry impeller.	Impellers
Spark plugs	Up to 300 hrs or annually (whichever comes first)	Use correct heat range and gap per model.	Spark Plugs
Fuel filter / water separator	Every 100 hrs or annually	Replace more often if storing fuel or seeing power loss.	Fuel Filters
Heat‑exchanger zinc anodes (closed cooling)	Inspect frequently; replace when 50% depleted	Critical for corrosion control; clean exchanger end caps when servicing.	Anodes
Flame arrestor (air intake)	Inspect/clean every 100 hrs; replace as needed	Keep airflow clear for smooth idle and acceleration.	Air Filters
Accessory belts	Inspect at 50–100 hrs; replace if cracked or glazed	Proper tension prevents charging and cooling issues.	Belts

*General guidance; consult your exact engine’s service schedule.

Frequently Used Parts Categories

Routine Service: Service & Maintenance Kits
Cooling System: Water Pumps and Impellers
Fuel System: Fuel Filters
Ignition / Electrical: Starters and Electrical Items
Exhaust & Induction: Manifolds and Air Intake
Corrosion Protection: Anodes
Sealing & Hardware: Gaskets

Common Symptoms & Quick Checks

Symptom	Check First	Related Parts
Overheat alarm or rising temp at idle	Raw‑water intake screen/sea strainer, impeller condition, hose kinks, thermostat, debris in cooler	Water pump/impeller, thermostat & gaskets, pump, hoses
Poor acceleration / loss of power	Clogged fuel filter, fouled spark plugs, dirty flame arrestor, heavy fouling on prop	Fuel filter, spark plugs, air intake, propeller
Hard starting / rough idle	Battery state, stale fuel, plug condition/gap, vacuum leaks/PCV, flooded‑start clear procedure	Spark plugs, fuel filter, electrical
Belt squeal / charging issues	Belt wear and tension, pulley alignment, alternator output	Belts, alternators

FAQs

Are parts interchangeable across different Indmar years and platforms?

Many routine service items (filters, plugs, belts, impellers) are shared across GM‑based Indmar small‑blocks, but details vary by displacement, fuel system, and cooling setup. Always verify using your engine serial number and component labels.

When should I replace the raw‑water impeller?

Inspect every season and replace at least every 1–2 seasons. Replace immediately if you see overheating, dry‑run events, or blade damage. Boats used in silty, sandy, or shallow water may require more frequent changes.

How often should I change transmission or V‑drive fluid?

Perform the first change at 10–20 hours and then annually, following the transmission manufacturer’s specifications (ZF Hurth, Walters, Ski‑Vee). Also inspect the transmission cooler and screens during service.

What information do you need to confirm part compatibility?

Please provide the Indmar engine serial number, engine family (e.g., Assault/Monsoon/RTP/6.0 PFI), cooling type (raw‑water vs. closed), transmission model, and current part markings (filter number, belt size, plug type).

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