ARCO IP004 Mercury / MerCruiser Replacement Impeller | Replaces 46-72774A89 / Sierra 18-3155

Part Details

• Part Number: IP004
• Brand: ARCO Marine
• Official Product Type: Flexible Replacement Impeller (impeller only — not a full pump kit)
• Replaces: Mercury / MerCruiser 46-72774A89
• Cross-References: Sierra 18-3155
• Pump Type: Mercury / MerCruiser two-piece plastic body seawater pump (V-belt driven)
• System: Raw-water / seawater cooling
• UPC: 693006030166
• Weight (approx.): 472 g / 1.04 lb

What This Part Is

ARCO IP004 is an aftermarket replacement flexible impeller for Mercury / MerCruiser two-piece plastic body seawater pumps where the original impeller reference is 46-72774A89 or Sierra 18-3155. It is the engine-driven raw-water pump impeller that draws cooling water through the MerCruiser seawater cooling circuit. Match by pump body type and impeller reference number — not by engine model alone.

Compatible Applications

Fitment is determined by the pump body style and original impeller number. Confirm all of the following before ordering:

• Pump housing is the two-piece plastic body design (V-belt driven)
• Original impeller or service reference is Mercury / MerCruiser 46-72774A89
• Application cross-references Sierra 18-3155
• Application is not the later one-piece brass-body MerCruiser seawater pump

This pump style is commonly associated with older MerCruiser V8 sterndrive and Bravo-drive engine installations with V-belt-driven seawater pumps.

Fitment Notice — Plastic vs. Brass Pump Body

There are two distinct MerCruiser seawater pump body designs that use different impellers:

• IP004 (this part) — for the two-piece plastic body pump (replaces 46-72774A89 / Sierra 18-3155)
• ARCO IP001 — for the later brass-body MerCruiser seawater pump (replaces 47-8M0104229)

If the pump housing is cracked, distorted, or deeply scored, replacing the complete pump is more reliable than fitting an impeller alone. See the ARCO WP004 complete pump assembly.

When This Part Needs Replacement

Replace the impeller during regular cooling-system maintenance or whenever inspection shows:

• Weak or absent cooling-water discharge at the exhaust
• Engine temperature rising under load
• Pump slow to prime or fails to prime
• Blades cracked, hardened, permanently bent, or torn
• Blade tips missing — trace all downstream components for fragments before returning to service
• Pump has operated without water supply (ran dry)
• Annual preventive cooling-system service

Installation Notes

• Disconnect the battery and allow the engine to cool before servicing
• Close the raw-water intake seacock
• Remove the pump cover — do not pry against the plastic housing
• Inspect the two-piece plastic body, cam surface, shaft, and cover plate for scoring, cracks, or distortion
• Locate and recover all missing blade fragments from downstream hoses, coolers, and heat exchangers before fitting the new impeller
• Lubricate the new impeller with glycerin or dish soap before installation — do not use petroleum-based lubricants
• Reassemble the pump cover evenly to avoid distorting the plastic housing
• Restore the water supply and confirm strong cooling-water discharge at the exhaust outlet immediately after startup

Cross-Reference Part Numbers

• ARCO: IP004
• Mercury / MerCruiser: 46-72774A89 / 72774A89
• Sierra: 18-3155
• UPC: 693006030166

Related Parts

• ARCO WP004 MerCruiser V8 Raw-Water Pump — complete two-piece plastic pump assembly (replace when housing is worn)
• Mercury MerCruiser Quicksilver Body/Impeller Kit 807151A14 — OEM plastic pump body and impeller kit
• Sierra 18-3150 MerCruiser Bravo / TRS Complete Cooling System Rebuild Kit — full cooling system service kit
• ARCO IP001 MerCruiser Brass Seawater Pump Impeller — later brass-body pump impeller (replaces 47-8M0104229)
• ARCO WP001 MerCruiser Brass Seawater Pump — later brass-body complete pump (if upgrading from plastic)
• Browse all impellers and pump service parts

Parts Desk Insights

Best use case: ARCO IP004 is the right choice for annual or post-overheating impeller service on older MerCruiser V8 engines equipped with the V-belt-driven two-piece plastic seawater pump — confirmed by matching original reference 46-72774A89 or Sierra 18-3155. It is a reliable aftermarket impeller at a lower price point than the OEM assembly.

Common issue: The most frequent ordering mistake is confusing the plastic two-piece pump with the later brass-body design — both pump types are common on MerCruiser V8 engines but use different impellers. IP004 is for the plastic pump; IP001 is for the brass pump. Confirm the pump housing material and match the original impeller number before ordering. If blade pieces are missing after removal, clear every downstream fitting, cooler, and heat exchanger before running the engine — a lodged fragment will destroy the new impeller immediately.