Examine foreign material found in cloth as well as that adhering to screen as
means of determining condition of engine.
Clean filters and screen as outlined in steps (a) and (b).
Prevention of Sludge Buildup. An inherent characteristic of internal combustion engines is the
generation of carbon solids. These carbon solids are moved about in the engine and oil systems as the oil
is pumped through its circuit. The oil ultimately becomes so loaded with carbon that deposits begin to
build up in areas where the oil is less turbulent, similar to sand deposited on sandbars in streams.
Commanders have an option of two courses to prevent this undesirable situation, adding cyclohexanone or
periodic oil dilution.
Cyclohexanone oil additive. Cyclohexanone has such a strong affinity for carbon solids
that it holds the carbon solids in suspension so long as the oil in the oil system contains 2 percent of
cyclohexanone by volume. Listed in the following paragraphs are certain procedures which must be
adhered to in this method of sludge prevention.
When cyclohexanone is added to oil in a storage or servicing unit, the oil and
additive must be circulated to ensure proper mixing.
New or newly overhauled engines. For new or newly overhauled engines,
perform the following procedures:
Engines with less than 100 hours operating time are considered new or
Maintain oil in oil system at 98 percent engine oil and 2 percent
cyclohexanone. These percentages are by volume.
Maintain these percentages in oil servicing units when this system is used. 2
Change oil every 300 hours of engine operating time, or at inspection nearest to 300
hours of engine operating time.
Engines with more than 100 hours (dirty engines). For dirty engines, perform the
Drain and flush entire oil system as outlined in applicable maintenance
Thoroughly clean all oil screens and strainers.
Service oil system with a mixture of 98 percent engine oil and 2
Repeat 1. 2 and 3, above, after first 50 hours of engine operating time, and clean
engine oil strainer at end of each 10 hours of engine operating time during this 50 hours.
All subsequent servicing of engine oil system shall be with a mixture prescribed in
Periodic oil dilution. This procedure is applicable to all engines having less than 130 hours
operating time since new or newly overhauled. Once periodic oil dilutions is adopted, its use should be
continuous throughout the life of the engine. When an engine has over 130 hours of operation since new
or overhaul, and over 65 hours of operation has elapsed since the last oil dilution (either periodic or for
cold weather starting), the engine will be considered a dirty engine, and use of periodic oil dilution may be
applied only after the engine has been desludged in accordance with the following:
Accomplish periodic dilution prior to first flight of day or after last flight of the
day. This does not imply that dilution will be accomplished prior to or after each flight in the day.