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
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
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
This is to prevent freezing and to protect the metal components.
A separate oil cooler is mounted in front of the radiator.
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
(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