Possible causes:

1. A leak in the jacket cooling water system (e.g. a leaking cylinder head gasket, a cracked liner, or a leaking cooling water connection) allowing water to enter the crankcase.
2. A leaking oil cooler (the cooling water leaking into the oil).
3. Condensation of water in the crankcase (from the blow-by of combustion gases containing water vapour, especially if the engine is run cold or at low load).
4. A leaking stuffing box/gland allowing water to enter.

Detection: the water is detected by the oil analysis (increased water content), by the oil appearing milky/emulsified, by a rise in the oil level in the sump, and by the presence of water at the bottom of the sump. The cause is found by inspecting the cooling water system, the liner, the head gasket, and the oil cooler, and by pressure testing.

Possible causes:

1. Bearing wear/failure: a main, big-end, or crosshead bearing wiping or failing, releasing white metal fragments into the oil.
2. A thrust bearing or a guide shoe wearing.
3. A bearing running with insufficient oil (starvation) or overloaded, causing wiping.

Detection: the white metal fragments are detected by the oil analysis (increased metal content, e.g. tin/lead/antimony) and by the presence of metallic particles in the oil filter and the sump. The cause is found by inspecting the bearings (clearances, condition) and the oil supply.

Possible causes:

1. The oil's base number (BN) has been depleted by neutralising the acidic products of combustion (sulphuric acid from the fuel sulphur), especially if the engine is burning high-sulphur fuel or if the oil is old.
2. Contamination of the oil (e.g. with water or fuel) reducing the BN.
3. The oil has been in service too long (the additive has been consumed).

Detection: the reduced BN is detected by the oil analysis (the BN value). The cause is found by checking the oil age, the fuel sulphur, and any contamination; the oil may need to be changed or the BN replenished.

Possible causes:

1. The oil's anti-oxidant additive has been consumed by oxidation, especially if the oil is overheated or in service too long.
2. Contamination (e.g. with fuel or water) accelerating the oxidation.
3. High operating temperatures causing the oil to oxidise.

Detection: the reduced anti-oxidation reserve is detected by the oil analysis (e.g. the oxidation level, the TAN, or the additive content). The cause is found by checking the oil temperature, the oil age, and any contamination; the oil may need to be changed.