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Home > Ordnance Documents and other related manuals > > Lubrication System.
Cooling System.
Characteristics And Operation of the HMMWV 's Lubrication System.

Troubleshoot The High Mobility Multi- Purpose Wheeled Vehicle (HMMWV)
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TROUBLESHOOTING THE HMMWV - OD1616 - LESSON 1/TASK 1
The cooling system on the HMMWV consists of the following components:
a radiator, surge tank, thermostat, 10 blade fan and drive clutch,
water pump, radiator hoses, pulleys and drive belts, and the radiator
shroud.
When the engine is cold, and the thermostat is closed, the coolant is
recirculated  through  the  water  pump  and  engine.
As  the  engine
coolant reaches 190 F, the thermostat opens allowing coolant to flow
through  the  radiator  before  returning  to  the  water  pump  and  the
engine.  Any air or vapor in the cooling system will be forced to the
surge tank under the liquid level and leave through the vent tube.
As the system cools, the extra coolant in the tank will be drawn back
to the radiator.  The normal operating temperature is between 190 F
to 250 F.
The  radiator  is  mounted  at  an  angle  of  approximately  45  to
accommodate the low silhouette of the vehicle.
The radiator holds
four gallons of coolant, while the surge tank holds half a gallon.
The radiator shroud channels the air flow between the radiator and
fan for more efficient operation.
The fan is mounted on the fan
drive clutch that activates the  fan when the coolant temperature
reaches approximately 220 F.  Normally, a 50-50 mixture of water and
ethylene glycol base antifreeze should be used in the cooling system.
This is to prevent freezing and to protect the metal components.
A separate oil cooler is mounted in front of the radiator.
This
cooler is divided into two parts.  The top half is for transmission
and transfer case oil, and the bottom half is for engine oil.
(2) When the cooling system pressure reaches approximately 15 psi,
a valve in the surge tank cap opens and lets excess pressure escape
into the atmosphere.  Another valve opens at approximately two inches
of mercury (vacuum) and allows air back into the cooling system.
f.
Lubrication System.
(1) Purpose of the Lubrication System.  The lubrication system in
an automotive engine provides a constant supply of oil to all moving
parts; this fresh oil is important to minimize wear, flush bearing
surfaces, and remove the localized heat
9






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