MIL-PRF-25478D
3.8.3 Pressure drop with air flow. The pressure drop across the oil cooler shall not
exceed 30 psi for Type IA and Type IB oil coolers with temperature regulation; 25 psi for Type
IA and Type IB oil coolers without temperature regulation; and 20 psi, unless otherwise
specified in the acquisition document (see 6.2), for Type II oil coolers with or without
temperature regulation.
3.8.4 Pressure drop without air flow. The pressure drop across the oil cooler with no air
flow shall not exceed the maximum allowable pressure for the engine oil scavenging pump
system as specified in the acquisition document (see 6.2).
3.8.5 Pressure resistance. The oil cooler shall withstand an oil pressure drop of 80 psi
with an oil temperature of less than 100oF and the bypass warm-up passage closed.
3.8.6 Pressure cycles. The oil cooler shall withstand 50,000 air pressure cycles applied
to the oil inlet with the oil outlet closed. An air pressure cycle is from 3 +3 psi to 60 +1 psi and
back to 3 +3 psi in 4.5 +0.5 seconds.
3.8.7 Ratings.
3.8.7.1 Rated oil flow. Rated oil flow shall meet the requirement specified in the
acquisition document (see 6.2).
3.8.7.2 Rated air flow. Rated air flow shall meet requirement specified in the acquisition
document (see 6.2).
3.8.7.3 Oil heat rejection. At rated oil flow, rated air flow, and the air inlet temperature
specified in the acquisition document (see 6.2), the total heat rejection (British Thermal Units per
minute) from the oil cooler shall be equal to or greater than total heat rejection specified in the
acquisition document (see 6.2).
3.8.8 Direction of air flow. Unless otherwise specified (see 6.2), the oil cooler shall
meet performance requirements with the air flow in either direction.
3.9 Environmental conditions.
3.9.1 Fluid resistance. The oil cooler shall withstand oil temperatures of -65o to 350oF
without leakage or permanent distortion.
3.9.2 Vibration. There shall be no leakage or permanent distortion of the oil cooler when
subjected to vibration. The vibration shall be maintained at an amplitude such that an
acceleration of 10g is imposed upon the oil cooler.
3.10 Maintainability. A drain device shall be provided on the oil cooler which shall
permit complete drainage of the oil cooler when installed in the aircraft.
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