Closed Cooling; Description; Antifreeze Recommendations - Mercury MerCruiser Product Applications Manual

Cooling System
3. Seawater flow should be solid with only tiny bubbles being acceptable (due to
pseudo-cavitation). If it is not:
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Closed Cooling

Description

Closed cooling is a standard feature on some models and is available as an accessory or
a factory installed option on others. When closed cooling is used, a mixture of antifreeze
and water is circulated through the water jackets in the engine block, cylinder heads, and
—on some applications—the exhaust manifolds to dissipate the heat. Refer to Water Flow
Diagrams. This coolant is then passed though a heat exchanger. Here the coolant rejects
heat to seawater (water in which the boat is being operated), which is simultaneously being
passed through the exchanger. The heat is then carried away by the seawater and
discharged overboard via the exhaust elbows. The design of the heat exchanger allows
for the transfer of heat, while ensuring that the two coolants are separated. In this manner,
the expensive engine components are never exposed to seawater, which can be corrosive
in salty, polluted, or mineral laden water areas.
Mercury MerCruiser's closed cooling systems are developed by the same people who
design our engines to ensure compatibility and the same high quality standards. Our
systems employ several exclusive features to provide unsurpassed cooling efficiency and
durability. An exclusive double-acting thermostat is used on V6 and V8 models, which
provides increased coolant velocity through the engine and heat exchanger to prevent hot
spots and improve performance. Mercury MerCruiser's heat exchangers also incorporate
several state-of-the-art designs to enhance the heat transfer between the coolants for an
additional margin of cooling capacity. Features like these allow our systems to continually
operate at WOT in water temperatures up to 38 °C (100 °F), where most after-market
systems fall short of this mark. This additional cooling capacity translates into longer
cooling system life with fewer problems regardless of where the boat is operated. Contact
your sales representative to order your closed cooling systems factory installed or refer to
the Mercury Precision Parts and Accessories Guide to obtain the part numbers for the
accessory kits.
The term full closed cooling, also known as full fresh water cooled or full FWC refers to the
use of an ethylene glycol mixture in the engine and the exhaust water jackets. The ethylene
glycol coolant mixture is circulated through the exhaust cooling passages as well as the
engine cooling passages.

Antifreeze Recommendations

Alcohol or Methanol based antifreeze or plain water, are not recommended for use in the
coolant section of the Closed Cooling System at any time.
Page 7A-10
Pickup located too far forward or outboard on the boat, allowing air to enter system.
Pickup located too close to the propeller or some other object and picking up
disturbed seawater flow.
Loose connection in the system allowing air to enter.
CAUTION
!
90-863758060 AUGUST 2006