Mercury MERCRUISER, Service Manual, Page: 416 / 566

1. Remove the boat from the water.
2. Using the hand pump or other air source, pump air into the system until both of the green indicators extend and the manual
release valve opens to relieve excess pressure. If one or both of the green indicators have not extended when the relief
valve opens, the corresponding air‑actuated drain valve has not opened and may be seized.
3. Release the compressed air from the air circuit by pulling up on the manual release valve ring.
4. Ensure both of the air‑actuated drain valves have closed by verifying that water is no longer draining from either valve. If
water continues to drain from an air‑actuated drain valve after the air pressure has been released, the valve is seized and
must be replaced.
Air Manifold
Removal
1. Remove the air manifold assembly from the air manifold bracket. Retain the washers and screws.
NOTE: The air lines are arranged in pairs of one gray and one black air line for each drain valve. To avoid reconnecting
these hoses incorrectly, note which side of the air manifold each pair of air lines is connected to before removing them
from the air manifold.
2. Disconnect the air lines from the air manifold. Push in and hold the plastic ring around the air line and pull the air line out of
the fitting.
a - Plastic ring
b - Air line fitting
c - Air line
Installation
1. Connect each pair of air lines to the proper side of the air manifold by fully inserting the air lines into the fittings on the air
manifold.
2. Install the air manifold assembly onto the air manifold bracket using the washers and screws. Tighten the screws to the
specified torque.
Description Nm lb‑in. lb‑ft
Air manifold assembly to bracket screw 2.3 20 –
3. Test the drain system for proper operation.
Drain Check Valve
General Information
Engines with standard cooling systems are equipped with drain check valves on the exhaust manifolds. Engines with
closed‑cooling systems are equipped with two drain check valves inline with the seawater hoses on the port side of the poppet
valve assembly.
•
The check ball within the valve is forced upward by water pressure from the seawater pump. This seals the drain fitting.
• When there is no water pressure from the seawater pump, such as when the engine is off, the check ball falls down into
the grooved drain fitting. This allows water to drain from the exhaust manifold, elbow, and seawater hoses (depending on
cooling system type).
a
b
a
c
50080
All Models
Page 6A-12 © 2016 Mercury Marine 90-8M0099748 eng DECEMBER 2015