Mercury MerCruiser OEM Water Drain System Air Pump 863057 | Air-Actuated Cooling Drain | 350 MAG 496 8.1L

Mercury MerCruiser OEM Water Drain System Air Pump — Part 863057

• Part Number: 863057
• Brand: Mercury Marine / MerCruiser (Genuine OEM)
• Official Product Type: Cooling System Parts — Water Drain System Air Pump
• System: MerCruiser air-actuated water drain system — cooling system drain
• Position: Connects to the drain system air manifold / valve assembly to supply actuating air pressure
• Quantity per Assembly: One pump per applicable drain system assembly
• Application: MerCruiser engines equipped with the air-actuated water drain system, including 350 MAG MPI Ski, 520, 540, 8.1L, and selected Bravo applications
• GTIN / UPC: 745061477988
• Weight: approx. 0.2 kg

Water drain system pump — not an engine air or emissions pump: 863057 is the manual hand pump used exclusively with the MerCruiser air-actuated water drain system. It provides the air pressure that opens the drain manifold / valve assembly, allowing the cooling system to be drained during service or winterization. Two engines of the same displacement may use different drain system configurations — confirm the Water Drain System diagram for your exact engine serial number before ordering.

What It Is

The 863057 is the genuine OEM manual air pump for the MerCruiser air-actuated water drain system. Mercury’s air-operated drain systems use a small hand pump to pressurize an air manifold mounted on the engine. When the manifold is pressurized, it opens a series of drain valves at key cooling system low points, allowing water to drain from the engine block and related cooling passages. This system is used for service drainage and winterization on equipped engines. The pump connects to the system’s air manifold and hose assembly and is a dedicated component — it is not an engine air pump, emissions pump, or bilge pump.

Compatible Applications

863057 is tied to the air-actuated water drain system, not simply to engine displacement. Confirm the Water Drain System diagram for your exact engine serial number before ordering — two engines of the same size may use different drain configurations.

350 MAG MPI Ski

• Serial 0M300000–0M316999
• Serial 0M317000–0W689999
• Serial 0W690000–1A089999

520

• Serial 0M970122 and up

540

• Serial 0M970866 and up

8.1L / 496 CID Inboard (Inline)

• Serial 1G300000 and up

8.1L / 496 CID Inboard (V-Drive)

• Serial 1G300000 and up

Bravo

• Serial 1G400000 and up — applicable air-actuated drain system configurations

Not sure it fits? Send us your MerCruiser engine serial number before ordering.

Related Drain System Components

Mercury Water Drain System diagrams show 863057 used with the following components. These are sold separately:

• 862969A2 — Air manifold / air valve assembly
• 863053T — Air manifold assembly (selected applications)
• 883503 — Service point cap
• 8630561 — Black air hose
• 8M0062605 — Green air hose / tubing
• 8M0062601 — Grey air hose / tubing
• 863059 — Air pump bracket
• 8634741 — Air pump bracket (selected configurations)
• 8634742 — Air pump bracket (selected configurations)
• 863863T — Actuator mounting bracket

Part Numbers

• 863057 — Current Mercury / MerCruiser OEM water drain system air pump

No superseding Mercury part number is confirmed in current OEM references for 863057.

When to Replace

Replace or inspect the air pump when:

• The pump will no longer build air pressure when operated
• The drain system actuator does not respond when the pump is used
• Air is leaking at the pump body or its connection to the system hose
• The pump handle or body is physically damaged or broken
• The drain manifold operates correctly with an external pressure source but not with the original pump
• The pump is missing from an engine’s drain system setup and needs to be restored

Before replacing the pump, inspect the air hoses, service-point cap, and air manifold for leaks — a failed hose or loose fitting can cause the same symptoms as a failed pump.

Service Interval

No fixed service interval for the pump itself — inspect on condition. The drain system should be tested at each winterization or seasonal drain service. If the pump fails to build pressure or the drain valves fail to open when the pump is operated, diagnose the pump, hoses, and manifold together rather than replacing components individually. Inspect all drain system air hoses for cracking, brittleness, or loose fittings at each annual service.

Installation Notes

• Confirm 863057 is present in the Water Drain System diagram for the specific MerCruiser engine model and serial number before ordering
• Connect the pump to the air manifold hose connection as shown in the Mercury Water Drain System diagram for the engine
• Inspect all drain system air hoses (8630561, 8M0062605, 8M0062601) for cracking or loose connections while the system is being serviced
• Confirm the service-point cap (883503) seals properly — a leaking cap prevents the manifold from pressurizing
• Check the air manifold (862969A2 or 863053T) for leakage before concluding the pump is at fault
• After reconnecting the pump, operate it and verify that all drain valves open and water actually drains from the engine before considering the drain complete
• Do not assume pumping alone confirms complete engine drainage — verify water flow from each drain point
• Follow the applicable Mercury MerCruiser winterization and drain procedure for the specific engine

Technical FAQ

Q: What does the 863057 air pump actually do?
It supplies the air pressure that operates the MerCruiser air-actuated water drain manifold. When you pump it, air pressure travels through the drain system hoses to the manifold, which opens a series of drain valves at cooling system low points on the engine. This allows the cooling passages to drain during winterization or service. Without the pump, or if the pump fails to build pressure, the drain valves will not open and the engine will not drain through the system.

Q: The drain system is not draining — is the pump the problem?
Not necessarily. The pump, the air hoses, the service-point cap, and the air manifold all need to work together for the system to operate. Before replacing the pump, inspect the hoses for cracks or loose connections, confirm the service-point cap seals properly, and check whether the manifold holds pressure. If an external air source operates the system correctly but the hand pump does not, the pump is likely at fault.

Q: Does 863057 fit all MerCruiser engines?
No. 863057 is specific to MerCruiser engines equipped with the air-actuated water drain system. Not all MerCruiser engines use this drain system, and two engines of the same displacement may use different drain configurations. Confirm the part number in the Water Drain System diagram for the exact engine model and serial number.

Q: Can I use a standard bicycle pump or air compressor instead of 863057?
The MerCruiser water drain system is designed for low-pressure air actuation through the 863057 hand pump. Mercury’s winterization procedures specify the correct method for the drain system. Consult the applicable Mercury service manual for the recommended procedure and any pressure limitations before using an alternative air source.

Parts Desk Insights

The most important thing to communicate about 863057 is what system it belongs to — customers searching for a pump sometimes assume it is an engine air pump or emissions-related component. It is the hand pump for the MerCruiser water drain system, and its only job is winterization and drain service. The most common troubleshooting situation is a drain system that will not actuate — in that case, the pump, hoses, cap, and manifold should all be checked together before ordering parts. A cracked hose or loose service-point cap is often the culprit rather than the pump itself. When 863057 genuinely fails, it typically means the pump body has cracked or the internal check mechanism no longer builds pressure.