ARCO WP004 MerCruiser V8 Raw-Water Pump | V-Belt Two-Piece | Replaces 46-72774A32 / Sierra 18-3600

ARCO WP004 MerCruiser V8 Replacement Raw-Water Pump

Part Number: WP004 (ARCO)  |  Brand: ARCO Marine  |  UPC: 693006030173

ARCO WP004 is a complete premium replacement raw-water pump for selected MerCruiser V8 marine engines equipped with a V-belt drive and two-piece seawater pump configuration. It restores raw-water circulation through the engine cooling system when the original pump assembly is worn, leaking, or no longer moving water effectively. Every ARCO pump is factory-tested before packaging.

Important: WP004 is an ARCO aftermarket replacement pump — not a genuine Mercury / Quicksilver OEM assembly. Fitment is specific to the V-belt, two-piece pump configuration. MerCruiser V8 engines with serpentine-belt drives or one-piece pump assemblies use a different pump. Confirm by the original pump number and accessory-drive layout before ordering.

Specifications

• Manufacturer Part Number: WP004
• Brand: ARCO Marine
• Product Type: Complete Raw-Water Pump Assembly
• Drive Type: V-belt
• Pump Configuration: Two-piece seawater pump
• System: Raw-water (seawater) engine cooling circuit
• Weight: 3,370 g / approx. 7.4 lb
• UPC: 693006030173

Compatible Applications

Fitment is confirmed by the existing pump number and accessory-drive configuration — not by engine displacement or model year alone. Confirmed for:

• MerCruiser V8 marine engines with V-belt accessory drive
• Engines equipped with the two-piece raw-water pump assembly
• Installations where the existing pump cross-references one of the following original part numbers:
  • 46-72774A32 / 72774A32
  • 72774A11 / 46-72774A11
  • 73823A7 / 46-73823A7
  • 59112A2 / 46-59112A2
  • 46-63450A2 (additional catalog reference)

Do not order by engine displacement alone. Later MerCruiser V8 engines with serpentine-belt drives and one-piece pump assemblies require a different pump. Confirm the belt arrangement and pump configuration from the engine serial number parts diagram before ordering.

Fitment Notice

Before ordering, verify all of the following for your installation:

• Application is a MerCruiser V8 engine
• Accessory drive uses a V-belt (not serpentine)
• Pump is the two-piece seawater pump configuration
• Existing pump number matches one of the cross-references above
• Hose sizes, port arrangement, and mounting hardware are compatible

When to Replace the Pump

Replace the complete pump assembly when any of the following are observed:

• Raw-water flow remains weak after installing a new impeller
• Pump housing is internally scored, corroded, or worn
• Pump shaft develops play or the bearing becomes noisy
• Water leaks from the shaft seal or pump body
• Belt pulley is damaged, loose, or misaligned
• Engine temperature rises despite a clear raw-water intake and serviceable impeller
• Pump assembly is physically damaged or seized
• Repeated impeller failures point to wear inside the pump housing

Installation Notes

• Confirm the engine serial number and original pump reference before beginning removal
• Close the raw-water intake seacock and disconnect the battery before working near the belt drive
• Record original V-belt routing and pulley alignment before removal
• Inspect the V-belt, cooling hoses, and clamps — replace worn items at the same service
• Align the pump pulley carefully with the remaining engine accessories before tensioning the belt
• Set belt tension per the MerCruiser service procedure
• Prime the pump and restore the raw-water supply before starting the engine
• If the previous impeller lost blade material, inspect downstream passages — hoses, coolers, thermostat housings — before startup
• Run the engine and verify strong raw-water discharge at the exhaust, correct temperature, and no leaks at the pump, hoses, or connections

Cross-Reference Part Numbers

• ARCO: WP004
• MerCruiser / Quicksilver: 46-72774A32, 72774A11 (46-72774A11), 73823A7 (46-73823A7), 59112A2 (46-59112A2), 46-63450A2
• Sierra: 18-3600
• GLM: 12093
• UPC: 693006030173

Related Products

• Mercury MerCruiser Water Pump Repair Kit 89984T5 — impeller and seal service kit for MerCruiser raw-water pumps
• ARCO WP001 MerCruiser Brass Seawater Pump | Replaces 8M0139984 / 862914A13 — ARCO replacement for current-style MerCruiser seawater pump
• ARCO IP001 Mercury / MerCruiser Seawater Pump Impeller | Replaces 47-8M0104229 — MerCruiser impeller replacement
• Sierra 3160-1 MerCruiser Sea Water Pump — Brass — alternative brass seawater pump for MerCruiser applications
• Quicksilver Water Pump Drive Pulley 8M0153706 — OEM MerCruiser seawater pump drive pulley
• Mercury MerCruiser Seawater Pump Pulley — 8M0150724 — MerCruiser seawater pump pulley

Parts Desk Insights

Best use case: WP004 is the correct choice when a MerCruiser V8 with the older V-belt, two-piece pump layout has a failed or leaking seawater pump and the original number cross-references the 72774A-series. It’s a complete factory-tested assembly, so you’re replacing everything — housing, shaft, seal, and impeller — rather than trying to salvage a worn housing with a new impeller. That matters on high-hour engines where the pump bore is often the real reason cooling performance has dropped despite repeated impeller replacements.

Common issues: The most frequent ordering mistake is not confirming the belt arrangement first. MerCruiser V8 engines were produced with both V-belt and serpentine-belt accessory drives, and the two pump types are not interchangeable. Check the existing pump and belt before ordering. The second issue is selection by engine displacement alone — multiple pump assemblies were used across MerCruiser V8 production runs, so matching the original 72774A32 / 72774A11 / 73823A7 / 59112A2 number from the pump casting or engine parts diagram is the only reliable fitment check.