Lubricant Degradation.

NAVAIR 17-15-50.4

TM 38-301-4

T.O. 33-1-37-4

CGTO 33-1-37-4

2-4. Lubricant Degradation.

a. Causes. Three basic factors control lubricant degradation: service time, operating temperature, and

contamination. Time and temperature are directly related. The useful life of a lubricant is extended when

equipment is operated at moderate operating temperatures and it is reduced when equipment is operated at

severe operating temperatures such as sustained engine operation at high loads or continuos operation with

high-sulfur fuel.

b. Effects. Breakdown of a formulated lubricant may be associated with oxidative deterioration of the

basestock or depletion or modification of a particular additive. Oxidative deterioration results in the formation of

acids, which promote corrosion and organic products. These products increase the viscosity of the oil. The effect

of a significant increase in viscosity is a reduction in the pumpability of the lubricant and the amount of lubricant

flow through delivery jets and ports. This reduces the lubricant ability to reduce friction, transfer heat, flush

contaminants, and maintain component cleanliness. Products resulting from oxidative deterioration may also

promote the formation of deposits, which can interfere with the operation of mechanical components and plug oil

filters and jets. Additive depletion results in the reduction of loss of the lubricant property which the additive was

intended to provide such as detergency, dispersany, and lubricating ability.

c. Contamination. Lubricant contamination may occur as a consequence of faulty maintenance practices,

poor handling techniques with new replacement oil, system-ingested contaminants, or system-generated

contaminants.

(1) System Ingested. In internal combustion engines, the main ingested contamination is dirt and/or

sand, which causes abrasive wear of mechanical components. The introduction of such contamination is usually

caused by a malfunction in the engine air induction system (damaged air filter, air hoses, etc.). This type of

contamination will normally be detected as high silicon during spectrometric analysis of system oil samples.

(2) System Generated. Several types of system-generated contaminants may occur. Examples

include antifreeze fluid, water, unburned fuel, and various products of combustion (blow-by products), which enter

the lubricant crankcase through the piston ring area. Wear-metals may also be considered a special type of

system-generated contaminant. The presence (or absence) of wear-metals is an indication of the integrity and

condition of the oil wetted mechanical system. If wear particles of appreciable size are generated, damage to

mating surfaces such as gears and bearings may occur.

(3) Contaminant Types. Table 2-3 lists the various types of lubricant contaminants, which may be

found, the significance of the contamination and the corresponding analytical methods for contaminant detection.

2-5. Equipment Analysis Requirements.

a. Engines. As a minimum, all Army and Marine engine samples shall be evaluated by four screening test

procedures: spectrometric analysis, viscosity, blotter spot test and test for water. If the results obtained for any

screening test are outside the evaluation guidelines, the laboratory evaluator shall consider the nature and

degree of the failing result and schedule additional testing as required. See table 2-4 for testing requirements.

See appendix D for Navy Ship requirements. A recommendation for maintenance action should not be made until

a resample has been requested to verify the suspected situation.

(1) Spectrometric values which exceed guidelines listed on applicable criteria tables should be

evaluated to determine whether a critical situation exists and the appropriate laboratory recommendation should

be assigned. For example, a verification sample that confirms excessive wear-metal concentrations is considered

a critical situation and warrants a recommendation for maintenance action. But an increasing wear trend on a

routine sample is not considered a critical situation; it warrants a recommendation for resampling.

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