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Figure 2-3. Effect of Periodic Fluid Addition and Fluid Change
TM-38-301-1 Introduction Theory Benfits Customer Sampling Procedures Programs and Reports Manual
Fuel Dilution (Flash Point).
NAVAIR 17-15-50.1
TM 38-301-1
T.O. 33-1-37-1
CGTO 33-1-37-1
of information that will assist the evaluator in making a maintenance recommendation. Incorrect reporting or
omission of even the most routine feedback information could adversely affect the evaluator's decision. Oil
additions can distort developing wear trends and therefore affect evaluator decisions. The addition of oil between
samples may result in abnormally low wear-metal results if the sample is taken immediately following an oil
addition. This may be particularly misleading if it occurs when a sample has been requested to verify high results
from a previous sample. Tank/sump draining actions done by the customer to reduce or eliminate
wear-metal levels will distort trends or mask actual conditions and are prohibited unless coordinated with
the monitoring laboratory. All of the above information may affect oil analysis results and should be promptly
reported to the laboratory. Details concerning oil analysis feedback requirements and procedures are contained in
Section III of this volume.
2-8. Physical Properties Identification and Measurement. The physical properties of lubricating fluids are altered
as lubricants degrade and/or become contaminated through service time and temperature, operational conditions
and faulty maintenance practices. Important physical properties of lubricants are viscosity, moisture content, flash
point, particulate level (solids), acidity/alkalinity and additive content. Physical property tests measure
contaminants such as water, atmospheric dirt, fuel, combustion blow-by products, and suspended particulate
matter commonly found in used crankcase oils. A brief description of the physical test methods currently in use
follows. The specific methods of analysis used to measure the various physical properties of used engine oils are
included in Volume II. Physical properties tests on lubricants may be selectively applied to service equipment as
determined by applicable service Program Managers.
a. Viscosity. Lubricating fluids are affected by high temperatures and aeration during service which
promote oxidation. This oxidation, if allowed to continue indefinitely, leads to increased viscosity, varnish and
sludge. Viscosity decreases are usually attributed to fuel dilution. The viscosity of used lubricating fluids is
determined by a viscometer which provides results/data that are converted to absolute viscosity and density
readings in centipoise x g/cm3. These readings may be compared to new oil viscosity specifications and provide
an indication of used oil condition.
b. Blotter Spot Test. This test is used to determine the presence of sludge in crankcase oils. One or two
drops when placed on a piece of blotter paper and allowed to spread will provide information on the presence of
sludge, the depletion of oil additives and/or moisture. The test is a rough estimate of sludge quantity but not of its
c.  Moisture Testing. Moisture or free water in an oil causes sludge formation In the crankcase and
prevents proper lubrication. Excess water causes flashing of metal surfaces under hot operating conditions, and
can cause engine failure. Moisture or free water in a transmission causes sludge formation or corrosion. Heat
transfer fluids and dielectric fluids require careful treatment due to their sensitivity to moisture, particulate and ion
contamination which can adversely affect equipment operation and degrade the fluid Insulating properties. Water
or moisture may be determined by either of the following methods:
(1)  Crackle Test. The crackle test is a qualitative test used for screening oil samples for the presence
of water contamination. After vigorous shaking, one or two drops of the used oil sample are dropped onto the
surface of a laboratory hot plate which has been heated to 150-177 degrees C (300-350 degrees F). A positive
test is indicated by an audible crackling and spattering of the oil. Use of this test in conjunction with other tests
can be used to identify probable sources of water contamination.

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