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top engine indicator shows the coolant temperature (COOLING TEMPERATURE).
The cooling system has 2 circuits. There is a main circuit and a bypass circuit.
For the main circuit, large diameter hoses and pipes connect the thermostat valve to the inlet of a
coolant radiator. The coolant radiator is located above and to the rear of the engine at the left. Large
hoses and pipes connect the outlet from the coolant radiator to an inlet on the engine crankcase at the
rear, left. This is the inlet to the engine coolant pump.
For the bypass circuit, large diameter hoses and pipes connect the bypass outlet from the thermostat
valve to the inlet for the coolant pump.
An coolant tank is located inboard and slightly above the coolant radiator. This is the highest point in
the system. A small diameter hose connects the highest point in the coolant radiator to the top of the
coolant tank. Another small diameter hose serves as overflow line to the exterior of the airplane.
A small diameter hose connects the bottom of the coolant tank to the inlet to the coolant pump. This
hose has an orifice.
A coolant level sensor is installed in the coolant tank. It operates the WATER LEVEL caution light in
the Auxiliary Engine Display (AED).
Pipes and hoses connect the thermostat valve to the inlet of the cabin heat heat-exchanger. The return
flow from the heat-exchanger connects to a tapping on the bypass circuit pipes adjacent to the
thermostat valve.
Both cabin-heat pipes have bleed points at the highest points of the cabin heat circuit.
AIRCRAFT
Cooling DA 40 Series
AMM
Page 4
20 Sep 2007 75-01-00 Doc # 6.02.01
Rev. 5
3. Operation
When the engine is cold, the thermostat valve closes the main circulation. The coolant pump moves
the coolant through the engine. The coolant becomes warm. The coolant flows out of the thermostat
valve through the bypass circulation pipes directly to the inlet of the coolant pump.
As the engine becomes hot, the temperature of the coolant increases. The thermostat valve senses
the increased temperature and starts to open. Some coolant goes through the bypass circulation
directly to the coolant pump inlet. Some coolant goes through the main circulation through the coolant
radiator. Air flowing through the coolant radiator cools the liquid coolant. The cool liquid returns to the
inlet of the coolant pump and mixes with the hot coolant from the bypass circulation.
The thermostat valve adjusts the flow of coolant through the main and bypass circulations to give the
correct temperature. It starts opening at 84 °C (183 °F) and opens fully at 94 °C (201 °F), allowing the
coolant to flow through the coolant radiator.
The connection for the cabin heat system supplies coolant at the outlet temperature from the engine
at all times.
AIRCRAFT
DA 40 Series
AMM
Cooling
Doc # 6.02.01
Rev. 5 75-01-00 Page 101
20 Sep 2007
Trouble-Shooting
1. General
This table tells you how to trouble-shoot the liquid cooling system. If you find the trouble in column 1,
do the repair in column 3.
This trouble-shooting table gives only troubles to the airplane parts of the cooling system.
Trouble Possible Cause Repair
Engine over-heats (CT caution
light illuminates).
Flat-belt worn or broken. Refer to the engine
manufacturer.
Coolant level low. Fill the cooling system. Refer
to Section 12-10.
Coolant leak. Look for leaks at all system
joints. Repair or replace
defective components.
Air in cooling system. Bleed the cooling system.
Radiator screen blocked by
foreign objects.
Remove foreign objects and
clean radiator screen.
Radiator screen damaged by
foreign objects.
Replace radiator.
Thermostat valve does not
work properly.
Refer to the engine
manufacturer.
Defective coolant pump. Refer to the engine
manufacturer.
Defective cylinder head
gasket.
Refer to the engine
manufacturer.
Cabin heat does not give hot
air.
Heat exchanger screen
blocked by foreign objects.
Remove blockage.
Heat exchanger screen
damaged by foreign objects.
Replace heat exchanger.
Defective cabin heat system. Trouble-shoot in accordance
with Section 21-01.
AIRCRAFT
Cooling DA 40 Series
AMM
Page 102
20 Sep 2007 75-01-00 Doc # 6.02.01
Rev. 5
Intentionally left blank
AIRCRAFT
DA 40 Series
AMM
Cooling
Doc # 6.02.01
Rev. 5 75-01-00 Page 201
20 Sep 2007
Maintenance Practices
1. General
This Section tells you about the maintenance practices for the components in the liquid cooling system.
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钻石40系列AMM 3(68)
