Mercury 25 EFI Service Manual page 304

Cooling System
Cooling System Specifications
Cooling system
Thermostat
Start to open temperature
Full open temperature
Valve lift
Cooling System Description
Cooling water enters the cooling system through the lower unit water inlets. The water pump driven by the driveshaft, forces
water through the water tube into the exhaust adaptor plate and filling the powerhead. Immediately 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 will begin to open
and allow 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.
Page 4D-2
Cooling System Specifications
© 2016 Mercury Marine
Water cooled ‑ thermostat control
60° ± 1.5 °C (140° ± 3 °F)
75° ± 1.5 °C (167° ± 3 °F)
3 mm (0.12 in.)
90-8M0105568 eng MARCH 2016