2-25. ENGINE COOLING TESTS
These Engine Cooling tests may be run any time you think you have an engine cooling
problem or if you were sent here by another test chain. Just follow the path, answering the
questions. Additional information and notes are given on the facing page when necessary.
Please note that this paragraph is NOT for diagnoses of problems with the temperature
sending unit or the gauge.
Once you are sure that the cooling system is OK, run the instruments test in Paragraph 2-32
to find out if the gauge is OK.
Fold-out FO-4 contains a functional diagram of the engine cooling system. This page may
be left open for reference while testing.
The engine cooling system is a pressure type cooling system with thermostatic control of
coolant circulation. The cooling system dissipates heat generated from combustion and
maintains the engine operating temperature at its most efficient level. When the engine is
cold and the thermostat is closed, coolant is recirculated through the water pump and
engine. As the engine coolant reaches 190°F (87.7°C), the thermostat opens allowing
coolant to flow through the radiator before returning to the water pump and engine. Any air
or vapor in the cooling system will be forced to the surge tank under the liquid level and
leave through a vent tube. As the system cools, the extra coolant in the tank will be drawn
back to the radiator. Normally a 50-50 mixture of water and ethylene glycol base antifreeze
will be used. The fan is activated when coolant temperature reaches 215°F (102°C). A
separate oil cooler is mounted in front of the radiator. This cooler is divided into two parts.
The top half is for transmission oil. The bottom half is for engine oil. When the cooling
system pressure reaches approximately 15 psi (103 kPa), a valve in the surge tank cap
opens and lets excess pressure escape to the atmosphere.
Change 1 2-155
PINTS PER GALLON
ARCTIC GRADE ANTIFREEZE
ETHYLENE GLYCOL (-60°F, -51.1°C)
Freezing point of -90°F (-67.7°C).
Issued ready for use and must not be
mixed with any other liquid.
ETHYLENE GLYCOL MIXTURE TABLE