Arco IP004 Mercury Replacement Impeller

Product Description

The ARCO IP004 is a premium replacement seawater-pump impeller kit for compatible Mercury MerCruiser engines using the older two-piece plastic raw-water pump body. It replaces Mercury impeller assembly 46-72774A89 and Sierra 18-3155, restoring the pump's ability to draw cooling water through the engine's raw-water cooling system.

Key Features

• ARCO part number: IP004
• Replacement impeller for Mercury MerCruiser applications
• Designed for the two-piece plastic seawater pump
• Replaces Mercury 46-72774A89
• Cross-references Sierra 18-3155
• New premium replacement component
• UPC / GTIN: 693006030166

Pump and Engine Compatibility

The ARCO IP004 is intended for Mercury MerCruiser installations equipped with the plastic two-piece seawater pump body. This pump style is commonly associated with older belt-driven MerCruiser raw-water pump systems, including compatible Bravo-drive engine installations.

The exact engine model should not be used as the only fitment check. Confirm that the installed pump is the two-piece plastic-body design and that the original impeller assembly matches Mercury 46-72774A89.

Fitment Notice

Before ordering, verify:

• The pump has a two-piece plastic housing
• The original impeller or service-kit number is 46-72774A89
• The application cross-references Sierra 18-3155
• The existing pump is not the later brass-body seawater pump
• The shaft, housing and cover are still serviceable

Do not confuse the IP004 with an impeller intended for the later one-piece brass MerCruiser pump. The pump-body construction is the fastest and most reliable visual distinction. If the housing is worn or damaged, consider replacing the complete pump with the ARCO WP004 instead.

When This Part Needs Replacement

Replace the impeller when:

• Exhaust-water discharge becomes weak
• Engine temperature rises under load
• The pump becomes difficult to prime
• The blades are cracked, hardened or permanently bent
• Blade tips are torn or missing
• The pump has operated dry
• The boat has been stored for an extended period
• Preventive annual cooling-system service is due

A damaged impeller can shed blade fragments into hoses, coolers and heat exchangers, so missing pieces should be located before the engine returns to service.

Installation Notes

• Disconnect the battery and allow the engine to cool.
• Close the raw-water intake seacock.
• Remove the pump cover and old impeller.
• Avoid prying against the plastic pump housing.
• Inspect the two-piece body, wear surfaces, shaft and cover.
• Retrieve any missing blade fragments from downstream cooling components.
• Lubricate the new impeller with a suitable installation lubricant.
• Align the hub carefully with the pump shaft.
• Replace the associated seals, O-ring or wear components as required by the pump service procedure.
• Reassemble the pump evenly to avoid distorting the plastic housing.
• Restore the water supply and verify strong cooling-water discharge immediately after startup.

Where the housing is cracked, distorted or deeply scored, replacing the complete pump may be more reliable than fitting an impeller alone.

Alternate / Cross-Reference Part Numbers

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

Compatible & Related Parts

When servicing the MerCruiser two-piece plastic seawater pump, consider these related parts:

• ARCO WP004 MerCruiser Replacement Water Pump – complete two-piece V-belt pump assembly (replace when housing is worn)
• Mercury MerCruiser Quicksilver Body/Impeller Kit 807151A14 – OEM plastic pump body and impeller kit
• Sierra Marine Water Pump Kit 18-3150 – MerCruiser Bravo / TRS complete cooling system rebuild kit
• Mercury MerCruiser Seawater Pump Impeller Kit 8M0137219 – OEM impeller kit (brass pump variant)
• ARCO WP001 MerCruiser Brass Seawater Pump – later brass-body pump (if upgrading from plastic)

Parts Desk Insight

The critical identifier for the IP004 is the plastic two-piece pump body. If the engine uses a later brass-body seawater pump, this is not the correct impeller. Matching Mercury 46-72774A89 or Sierra 18-3155 provides the safest confirmation.