Diesel engine oil will absorb combustion heat and friction heat during the working process, and the oil temperature will rise, but generally it will not be higher than 90 °C. If the oil temperature is too high, there are usually the following reasons:

(1) The cooling system is faulty. For example, there is too much scale on the cooling water jacket, and the heat dissipation is poor.

(2) The lubrication system oil circuit is blocked. If the oil filter is clogged, the resistance increases, and some of the oil cannot pass through the strainer and the radiator, but directly enters the main oil passage, causing the oil temperature to rise.

(3) Air leakage from the compression system. If the piston ring and the cylinder liner wear out, the gap increases, or the piston ring opening gap is too large, resulting in a tight seal, and high temperature gas enters the crankcase.

(4) The heat dissipation of the collective and oil pan is poor. For example, after long-term use of the diesel engine, thick oil or mud is adhered to the outside of the body or the oil pan, and the heat is difficult to dissipate.

(5) The influence of the engine's own working conditions. For example, the engine is overloaded for a long time, the oil pump is damaged, or the gap between the main bearing and the connecting rod bearing is too small.

Excessive oil temperature will not only make the oil thinner, the oil pressure will drop, the anti-wear performance of the lubricating oil will decrease, the wear of parts will accelerate, and the sealing effect will be lost, resulting in air leakage of the cylinder and the piston ring, and increase the oil consumption. Therefore, once the oil temperature is too high, it is necessary to find out the cause and promptly remedy it to avoid affecting the normal operation of the engine.