Mercury MERCRUISER, Service Manual, Page: 55 / 566

1. Insert a small wire repeatedly to ensure that vent holes, water drain holes, and passages are unobstructed and open.
Sterndrive water drain holes
a - Speedometer pitot tube
b - Trim tab cavity vent hole
c - Trim tab cavity drain passage
d - Gear housing water drain hole (1 each ‑ port and starboard)
e - Gear housing cavity vent hole
f - Gear housing cavity drain hole
NOTICE
The universal joint bellows may develop a set when stored in a raised or up position, causing the bellows to fail when
returned to service and allowing water to enter the boat. Store the sterndrive in the full down position.
2. Lower the sterndrive unit to the full down/in position.
3. For additional assurance against freezing and rust, after draining, fill the cooling system with propylene glycol mixed to the
manufacturer's recommendation to protect engine to the lowest temperature to which it will be exposed during freezing
temperatures or extended storage.
IMPORTANT: Mercury MerCruiser requires that propylene glycol antifreeze, mixed to the manufacturer's instructions, be
used in the seawater section of the cooling system for freezing temperatures or 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.
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)
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.
b
a
d
e
f
c
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Maintenance
90-8M0099748 eng DECEMBER 2015 © 2016 Mercury Marine Page 1C-39