Because of this, parts have insufficient oxygen, causing incomplete combustion and generating soot (carbon). There is tendency for a large amount of soot to be generated when depressing the accelerator pedal heavily in particular, such as when starting or going up hills, as large amount of fuel is injected and pockets with insufficient oxygen are more likely to occur.
The ejected soot not only causes air pollution but also has adverse effects on the human body. Therefore, at the time of vehicle inspection, it is necessary to inspect whether the soot discharge is exceeding the standard or not.
This soot is not only ejected as exhaust gas, but is also absorbed into engine oil, degrading the oil. That's why engine oil for diesel engines contains many additives.
Additionally, if large amount of soot enters into the oil, wear of engine parts will accelerate and oil consumption will increase.
Therefore it is extremely important to inspect the oil on a daily basis.
Engine oil classifications for diesel engines
The diesel fuel contains sulfur and oil. Because of the sulfur content, sulfuric acid is generated through combustion.
This sulfuric acid is strong, corroding bearings, oxidizing oil and generating sludge. Therefore, diesel engine oil is required to have clean dispersiveness to prevent the generation of sludge and the ability to neutralize acid. Engine oil for diesel engines are classified into several standards, making it possible to know to which extent these performances are satisfied.
JASO classification
JASO is the Japanese Automotive Standards Organization. In Japan, API service classifications are commonly used as a quality standard for vehicle diesel engine oils, but due to design differences between Japanese and US engine, quality standards for engine oils more suitable to Japanese-made diesel engines were set.
There were newly set for vehicles equipped with post-treatment devices such as Diesel Particulate Filters (DPF) which complied with new short-term emission regulations, with DH-2 for trucks and buses, and DL-1 for passenger class vehicles.