Water. When operating aircraft at temperatures below freezing, or when temperature may drop below the
freezing point, open the oil tank sump drains sufficiently to drain off any accumulation of water.
Solids. Carbon and metallic particles are the two most common types of solid contaminants.
Carbon. Frequently, carbon breaks loose from the interior of the engine in large pieces which have the
outward appearance of metal. However, carbon can be distinguished from metal by placing the foreign material on a flat
metal object and hitting with a hammer. If material is carbon, it will disintegrate when struck with a hammer, whereas
metal will either remain intact or change shape, depending upon its malleability.
The information in the following paragraph is not intended to be a substitute for, nor release
from, the requirement for compliance with the Army Oil Analysis Program (AOAP) directed
in accordance with TB 43-0106.
Metallic Particles. Metal particles found in an engine may be of five kinds: steel, tin, aluminum, silver, and
copper (or bronze). A visual inspection as to color and hardness will occasionally be sufficient to determine the kind of
metal present When visual inspection does not positively identify the metal, the kind of metal present may be determined
by a few simple tests performed with a permanent magnet, electric soldering iron, and approximately 2 ounces each of
hydrochloric acid and nitric acid as follows:
(a) Steel particles. Steel particles can be isolated by means of a permanent magnet.
(b) Tin particles. Tin particles can be identified by their low melting point. A soldering iron should be cleaned,
heated to approximately 500 °F (260 °C), and tinned with 50-50 solder (50% lead to 50% tin). Wipe off
excess solder. A tin particle dropped on heated iron will melt and fuse with the solder. Take care to avoid
excessive overheating of iron during this test
Exercise care in handling acid. Acid can bum if splashed on skin.
Aluminum particles. Aluminum particles may be identified by their respective reaction with hydrochloric
acid. When a particle of aluminum is dropped into hydrochloric acid it will fizz with a rapid emission of
bubbles. The particle will gradually disintegrate and form a black residue (aluminum chloride).
Silver and copper. Silver and copper (or bronze) may be identified by their respective reactions in nitric
acid. When a silver particle is dropped into nitric acid, it will react rather slowly, producing a whitish fog in
the acid. When a particle of copper (or bronze) is dropped into nitric acid it will react rapidly, producing a
bright green cloud in the acid. There is no need in this instance to separate copper from bronze.
Prevention. Care should be taken in the servicing and maintenance of oil systems to prevent contamination.
The oil tank filler cap must be installed correctly and locked in place. Oil should be drained, inspected, and changed to
ensure a dean supply of oil for the engine.
3-6. Oil System Maintenance. Oil System types and general oil system component maintenance are explained in the
Types, Wet-sump and dry-sump oil systems are used in reciprocating and turbine engine aircraft for lubrication.
Reciprocating engines. Reciprocating engines use both wet-sump and dry-sump systems to lubricate
internal moving parts.
Wet-sump. This system consists of a sump or pan in which the lubricating oil is contained. The oil is
drawn from the sump to lubricate the engine by an oil pressure pump. After lubricating the various units on which it
sprays, the oil drains back into the sump and the cycle is repeated. Figure 3-2 shows a typical wet-sump system.
The main disadvantages are: ·
The oil supply is limited by the sump (oil pan) capacity.
Provisions for cooling the oil are difficult to arrange because the system is a self-contained unit.
Oil temperatures are likely to be higher on large engines because the oil supply is so dose to the engine and is
continuously subjected to the operating temperatures.
Change 1 3-3