Mercury 4-Stroke 502HP Marine Engine Parts

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This page is tailored for Mercury 4‑Stroke 502HP marine engines and helps you find compatible parts and practical service information. Below you’ll find maintenance tips, frequently replaced parts, and troubleshooting guidance. You can also browse the main MerCruiser collection for a wider range of components. 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.

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How to Identify Your 502HP Model

Locate the engine serial plate on the starboard side of the engine block or on the flame arrestor/engine cover decal; the transom assembly and sterndrive also have serial labels.
Read the model/serial information to confirm whether your package is carbureted or MPI/EFI, and note Bravo drive family (Bravo One, Two, or Three) for correct gearcase parts.
For 4‑stroke big‑block platforms (8.2L class), note Gen V/VI differences; some cooling, ignition, and accessory parts vary by generation and serial break.
Record key options such as closed‑cooling (heat exchanger) vs raw‑water cooling, and whether your controls are mechanical (non‑DTS) to ensure harness and sensor compatibility.

Platform Overview

8.2L V8 (502 Magnum / HP-series) Engine

Feature	Description
Configuration	8.2L V8 4‑stroke, carbureted or MPI/EFI; typically paired with Bravo sterndrives; raw‑water or closed‑cooling variants.
Common Models	502 Magnum (carb or MPI), 8.2L big‑block packages; Mercury Racing HP500/HP525 EFI style packages in similar families. Always verify by serial.
Advantages	High torque, strong mid‑range, robust components with wide parts availability.
Notes	Many accessories align with 454/7.4L and later 8.2L families, but cooling, ignition, and mounting hardware often depend on generation and serial breaks. Non‑DTS control systems are common on these packages.

Bravo Sterndrive & Transom Assembly (Bravo One/Two/Three)

Feature	Description
Configuration	Heavy‑duty Bravo transom/gimbal with Bravo One, Two, or Three drive units; gear ratios and prop configurations vary by application.
Common Models	Bravo One (performance), Bravo Two (thrust/utility), Bravo Three (dual‑prop for lift and control). Verify drive family before ordering anodes, seals, and propellers.
Advantages	High load capacity and durability for big‑block torque; broad parts support.
Notes	Anode sets, prop hardware, and gearcase seals differ by Bravo variant. Inspect serial tags on both transom assembly and drive.

Routine Maintenance & Service Parts

Intervals below are general guidelines for typical recreational use. Always follow the official service manual for your exact engine/drive serial number and operating environment.

Item	Interval*	Remarks	Parts Link
Engine oil + filter	100 hours or annually	Use marine‑rated oil per manual; warm engine before change for complete drain.	MerCruiser Oil Filters
Gear oil (Bravo drive)	100 hours or annually	Inspect for water intrusion/metal on magnet; change sooner after heavy use.	MerCruiser Service & Maintenance Kits
Spark plugs	Inspect annually; replace ~300 hours/3 years	Check gap and heat range per model; misfire under load often traces to worn plugs.	Spark Plugs
Fuel filter / water separator	100 hours or annually	Replace more often if fuel contamination is suspected; prime system after service.	MerCruiser Fuel Filters
Raw‑water impeller / kit	200 hours or every 2 seasons	Replace sooner in sandy/silty water or if overheat/weak tell‑tale is observed.	MerCruiser Impellers
Anodes (zinc/aluminum/magnesium)	Inspect every 3 months; replace when 50% depleted	Match anode alloy to water type (salt/brackish/fresh) and Bravo variant.	MerCruiser Anodes
Propeller inspection & hub	Check each trip; service annually	Remove for fishing line checks; verify hub integrity and correct pitch for load.	MerCruiser Propellers
Bellows & transom service	Inspect annually	Check u‑joint/exhaust bellows, gimbal bearing, and grease points to prevent leaks.	Bellows

Frequently Used Parts Categories

Routine Service: MerCruiser Service & Maintenance Kits
Cooling System: MerCruiser Impellers
Fuel System: MerCruiser Fuel Filters and MerCruiser Fuel Pumps
Ignition / Electrical: Starters and MerCruiser Alternators
Corrosion Protection: MerCruiser Anodes
Propulsion: MerCruiser Propellers
Gaskets & Seals: MerCruiser Gaskets and Lower Unit Seal Kits

Common Symptoms & Quick Checks

Symptom	Check First	Related Parts
Weak water stream or overheat alarm	Inspect intake screens for blockage, raw‑water impeller wear, and thermostat function.	Water pump impeller kit, thermostat, intake screens, anodes (fouling).
Poor acceleration or power loss	Check prop condition/pitch, fuel filter restriction, and spark plug wear.	Propeller/hub, fuel filter/water separator, spark plugs.
Hard starting or rough idle	Verify battery health, stale fuel, plug condition, and vacuum leaks.	Spark plugs, fuel filter, ignition components, hoses/gaskets.
Gearcase noise or metal in gear oil	Confirm oil level/condition; inspect for water intrusion and prop‑shaft seal damage.	Lower unit seal kit, prop hardware, gear lube, bearings (inspection).
Trim won’t raise/lower	Check fluid level, switches, and pump motor operation; inspect for corrosion at connectors.	Trim motor/pump, relays/switches, harness/connectors.

FAQs

Are parts interchangeable between different years or platforms?

Some accessories overlap across 454/7.4L and 8.2L (502) platforms, but many items change at serial breaks and by Bravo drive variant. Always verify engine and drive serial numbers before ordering.

When should the raw‑water impeller be replaced?

As a baseline, every 200 hours or two seasons—sooner if you operate in sandy/silty water, see reduced flow, or experience an overheat event.

How often should I change Bravo gear oil?

Every 100 hours or annually. Inspect for water contamination and metal on the magnetic drain plug; service sooner after impacts or extended high‑load operation.

What information helps confirm part compatibility?

Provide engine serial number, drive family (Bravo One/Two/Three), cooling type (raw vs closed), control type (mechanical vs DTS), and clear photos of the nameplate and the part location.

Ready to find parts? Browse the main MerCruiser collection and filter by horsepower, year, and model to zero in on components that fit your Mercury 4‑Stroke 502HP package.

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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.