Diesel oil 15w40 and 20w50 are two different oil grades. The number in front of W represents the low temperature starting performance. The smaller the value, the better the performance. The minimum starting temperature of 15W goes to -18 degrees, while 20W is only -11 degrees; the following numbers Represents the viscosity of the oil. The larger the value, the more viscous it is. 50 to 40 can adapt to higher working temperatures.
Whether the diesel engine uses 40 or 50 oil in summer should be determined according to the specific situation. It is not that the higher the viscosity, the better. Car owners should choose according to the temperature conditions in the region. If the temperature is higher, of course, the oil with higher viscosity can better protect the engine and enable it to have a good working environment in summer.
If the local temperature is not very high and the viscosity required by the engine is only 40, then there is no need to use a higher viscosity oil, which will only increase fuel consumption and lack of power.
In addition, the grades of diesel oil are roughly divided into: CA, CB, CC, CD, CE, CF, CF-4, CG-4, CH-4, CI-4, CJ-4. Different models of diesel oil grades indicate different oil grades and corresponding applicable models. That is to say, the further back the letters are arranged, the higher the oil quality grade, and so on. So it is not difficult for us to come up with the highest grade of diesel oil: CJ-4.
The following is the classification table of some diesel oil grades and their applicable models
| Diesel engine grade | Applicable Model |
| CE | Engines under low-speed high-load, high-speed and high-load conditions |
| CD | turbo diesel engine |
| CF-4 | High-speed, heavy-duty, long-cycle diesel engines |
| CG-4 | Diesel engines with a fuel sulfur content of less than 0.05% |
| CH-4 | Bimetallic piston diesel engine |
| CI-4 | Diesel engine with low temperature exhaust gas in circulation system |
Diesel oil grade model description: The beginning of the English letter C represents diesel oil. The further the letters are arranged, the higher the oil quality grade. The general diesel engine can use the CD grade oil, and the supercharged diesel engine requires the oil quality of the oil. To be higher, you need to use CF-4, where -4 means that the oil is suitable for four-stroke diesel engines.
At present, my country's diesel engine oil is mainly based on CF-4. CF-4 is used in high-speed direct injection diesel engines and outperforms CF in terms of fuel consumption and piston deposition. It is suitable for diesel engines burning high sulfur content fuels, especially for heavy-duty trucks. Compared with CF, CF-4 oil has more comprehensive performance, and the oil change interval of CF-4 is twice that of CD.
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