Mercury 15 EFI FourStroke, Service Manual

Page: 217 / 406

Cooling System Specifications
Parameter Specification
Thermostat
Start to open temperature 50–54 °C (122–129 °F)
Full open temperature 60–64 °C (140–147 °F)
Valve lift 4.0 mm (0.157 in.)
Water pressure at idle 9–18 kPa (1.3–2.6 psi)
Water pressure at WOT 59–118 kPa (8.6–17.2 psi)
Cooling System Description
Water enters the cooling system through the lower unit water inlets. The water pump, driven by the driveshaft, forces water
through the water tube, through the driveshaft housing, and into the powerhead. After the powerhead is filled with water, a
small steady stream of water exits the water pump indicator.
Water flow through the block is controlled by the thermostat. As the water temperature rises, the thermostat opens and allows
water to pass by the thermostat, into the engine cooling jacket. The water then passes into the exhaust chamber area of the
driveshaft housing, cooling the exhaust gasses, and on through the exhaust outlet of the propeller.
To allow complete passage filling and to prevent steam pockets, all cooling passages are interconnected. Small passages are
incorporated into the cooling system, to allow the cooling system to drain while the outboard is in a normal operating position.
General Troubleshooting
For general troubleshooting information, including connecting and using the CDS G3 diagnostic tool, refer to
Section 1E
‑
General Troubleshooting
.
Thermostat
Thermostat/Electrical Bracket Removal
The thermostat housing and electrical bracket are both secured to the engine block with the same screws. They are removed
and installed together.
1. Release the reusable cable tie at the top of the electrical bracket.
2. Clip the cable tie at the bottom of the electrical bracket.
3. Remove the two screws that secure the thermostat housing and electrical bracket to the engine block.
a - Cable tie
b - Screw (2)
c - Thermostat housing
d - Reusable cable tie ‑ do not cut
e - Fuse housing
f - Electrical bracket
4. Remove the thermostat from the engine block.
5. Inspect the thermostat. Replace if damaged, seized, or corroded.
Testing the Thermostat
1. Tie a piece of thread or other nonconductive material onto the thermostat.
2. Suspend the thermostat in cold water.
3. Suspend a thermometer in the water.
IMPORTANT: Do not allow the thermometer to contact the heating surface of the container. An inaccurate temperature
reading may result.
a
b
c
b
d
e
f
63057
Cooling System
Page 4D-2 © 2018 Mercury Marine 90-8M0125265 eng NOVEMBER 2017