Mercury MERCRUISER, Service Manual, Page: 46 / 566

Checking the Seawater Pickups
Ensure that the water inlet holes for the seawater pickup are clean and unobstructed.
Typical through-the-hull seawater pickup Typical through-the-transom seawater pickup
a - Water inlet holes
Draining the Seawater System
Draining the Raw Water
!
CAUTION
Water can enter the bilge when the drain system is open, damaging the engine or causing the boat to sink. Remove the boat
from the water or close the seacock, disconnect and plug the seawater inlet hose, and ensure the bilge pump is operational
before draining. Do not operate the engine with the drain system open.
IMPORTANT: Only drain the raw water section of the closed cooling system. Raw water is sometimes referred to as seawater.
IMPORTANT: The boat must be as level as possible to ensure complete draining of the cooling system.
IMPORTANT: The engine must not be operating at any point during the draining procedure.
IMPORTANT: Mercury MerCruiser requires that propylene glycol antifreeze, mixed to the manufacturer's instructions, be used
in the raw water section of the cooling system during freezing temperatures or for extended storage. Ensure that the propylene
glycol antifreeze contains a rust inhibitor and is recommended for use in marine engines. Be certain to follow the propylene
glycol manufacturer's recommendations.
Air Actuated Single‑Point Drain System (Closed Cooling, Inboard Models)
The following instructions apply to draining procedures performed on engines in vessels that are in the water. For vessels that
are not in the water, you do not need to close the seacock (if equipped) or remove and plug the water inlet hose.
1. Close the seacock (if equipped) or remove and plug the water inlet hose.
2. Remove the blue plug from the heat exchanger.
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Maintenance
Page 1C-30 © 2016 Mercury Marine 90-8M0099748 eng DECEMBER 2015