b. Adding MIL-L-23699 oil to MIL-L-7808 oil which is used at very low ambient temperatures will increase the oil
viscosity which may cause oil starvation at cold temperatures (-40 , -40 or colder).
3-5. Conversion to MIL-L-23699.
For most turbine engine powered aircraft components, MIL-L-23699 has replaced MIL-L-7808 oil at temperatures above -
25 (-32 ). To reduce potential problems and provide for a more orderly conversion to MIL-L-23699 oil, the following
is recommended: Use MIL-L-23699 oil in all new and newly overhauled turbine engines.
3-6. Compatibility of Turbine Oils.
MIL-L-7808 and MIL-L-23699 oils are required by specifications to be compatible with each other. However, adding MIL-
L-7808 oil to a system which has been converted to MIL-L-23699 should be avoided, if possible, since the addition of
MILL-7808 oil will lower the concentration of MIL-L23699 oil and thus will tend to nulify the benefits derived from the MIL-
L-23699 oil. In addition, indiscriminate mixing of the two oils may result in pressures and flow limits different from the
published values for either oil. When operating conditions necessitate reservicing with MIL-L-7808 the system or
components should be drained and reserviced as soon as MIL-L-23699 oil is available.
During the initial transitioning period some residual MIL-L-7808 oil will remain in the engine oil systems and some
degradation of the MIL-L23699 is considered acceptable in order to eliminate costly and time consuming flushing
3-7. Color of MIL-L-23699 Oils.
The approved MIL-L-23699 oils vary in color depending on the supplier. The color of these oils is due in part to the
additives used by different manufacturers. Some of the additives used may turn the oil a dark color or in some cases
give the oil a reddish appearance. Therefore, the color of the oil should not be used as the basis for deciding if the
mechanical condition of engines or components is suspect. In the past, color has been used to detect hydraulic fluid
contamination of the oil in an engine. However, chemical methods are available for this purpose and should be used if
3-8. Turbine Engine Oil Changes.
a. Oil change intervals for turbine engines will vary from model to model depending on the operating oil
temperature resulting from specific airframe installations and engine configurations. MIL-L-23699 should provide a much
greater oil life than MIL-L-7808. Operating experience will be used as a guide in determining if oil changes are
necessary between overhauls. In the interim the recommendations of the applicable service instruction manual should
b. When changing from MIL-L-7808 oil to MIL-L-23699 oil, the following procedure should be used if specific
instructions are not provided in the applicable aircraft maintenance manual:
(1) Drain the MIL-L-7808 oil from the component oil system.
(2) Inspect, clean, and reinstall all component oil filters and strainers.
(3) Fill component oil system with MILL-23699 oil, and operate aircraft for a period of 30 minutes to one hour.
(4) Shutdown aircraft.
(5) Inspect, clean, and reinstall all component oil filters and strainers. If oil filter(s) was heavily contaminated,
comply with (6) through (10) below. If oil filter was not heavily contaminated, comply with (8) through (10) below.
(6) Drain all MIL-L-23699 oil from component oil system and dispose of oil.
(7) Fill component oil system with new MIL-L-23699 oil and release aircraft for service use.
(8) After 5 hours of aircraft operation, inspect and clean all component oil filters and strainers.
(9) After 15 hours aircraft operation since oil change, inspect, clean, and reinstall all component oil filters and
(10) Revert to normal filter and strainer inspection interval.
c. When changing from MIL-L-23699 oil to MIL-L-7808 oil, the following procedure should be used: