MIL-PRF-21260 Lubricating Oil, Internal Combustion Engine, Preservative Break-InThis performance specification covers engine oils suitable for preservation, break-in, and lubrication of reciprocating internal combustion engines of both spark-ignition and compression-ignition types, and of power transmission fluid applications in equipment used in combat/tactical service \(see 6.1, 6.7 and 6.9\).

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MIL-PRF-21260E

3.3.2 Foaming. The oil shall not produce foam which will cause inadequate lubrication,

cavitation, overflow loss of lubricant, mechanical failure, or any other detrimental effect that

compromises performance.

3.3.3 Oxidation and wear protection characteristics. The oils shall protect internal

loaded engine components against excessive wear and oxidation.

3.3.4 Soot protection. The oils shall protect internal loaded diesel engine components

against excessive wear caused by the presence of soot.

3.3.5 Ring-sticking, wear, and accumulation of deposits. The oils shall prevent the

sticking of piston rings and port clogging, and shall minimize the wear of cylinders, rings, and

loaded engine components such as cam followers, valve rocker arms, rocker arm shafts, and the

oil pump and fuel injection pump drive gears.

3.3.6 Friction retention characteristics and wear. The oils shall maintain a stable

coefficient of friction and shall minimize distress and wear during use in power shift

transmissions and other cooled friction compartments, or hydraulic systems such as steering and

disconnect clutches.

3.3.7 Seal compatibility. The oils shall minimize the deterioration of seal and friction

materials.

3.3.8 Dispersancy characteristics. The oil shall minimize engine deposits and increased

oil viscosity by ensuring the stable dispersement of soot, produced during diesel combustion, in

the lubricating oil.

3.3.9 Corrosion. The oils shall meet the requirements as specified in 3.3.9.1

through 3.3.9.3.

3.3.9.1 Bearing corrosion. The oils shall not corrode copper-lead alloy bearings.

3.3.9.2 Metal corrosion. The oils shall not corrode metals.

3.3.9.3 Acid neutralization. The oils shall neutralize the corrosive effects of acid.

3.3.10 Shear stability. SAE 15W-40 grade oil shall demonstrate shear stability.

3.4 Interface requirements. The oils shall be compatible with oils previously qualified

under MIL-PRF-2104, MIL-PRF-21260, and MIL-PRF-46167.