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Engine Oil Grades for Diesel Engine

Diesel bulldozer in the desert

Engine oils can be specified by two properties or characteristics. They can specify their performance capabilities and their viscosity. For any typical motor, the correct viscosity to be chosen will be dependent on the highest ambient temperature during operation and also the lowest start up temperature. Both of these can typically be found in your vehicle’s operation manual. The original equipment manufacturer will usually list a chart of recommended engine oils viscosity grades for the ambient temperature conditions that are likely to be experienced.

Choosing the best engine oil grades for diesel engine operations is easier once you know what the numbers and letters mean. When looking at an engine oil recommendation chart showing SAE grades, you will see that the lower SAE “W” are the ones most specified for cold temperature or start ups at lower temperatures. For example, an SAE 5W or an SAE 10W would be best for start up at lower temperatures. The “W” in the engine oil means it is for winter. The first number before the W specifies it as a cold weather viscosity. The lower the number, the less viscous the engine oil will be at colder or lower temperatures. A 5W engine oil, for example, will have a lower viscosity and will flow easier at colder start up temperatures than a motor oil with a designation of 15W. The higher number that appears after the W illustrates the oil’s viscosity during hot temperatures. The higher the number, the more viscous (thicker) the oil will be at the specified temperature shown on the chart. The chart will also show SAE grades of engine oil without the W. These are single grade, or non-W grade engine oils. These typically find use when ambient temperatures are higher.

Diesel motor.
It is important to determine the range of ambient operating temperatures that diesel engines will be run. With this knowledge, the proper engine oil viscosity can be chosen.








The majority of diesel engines that operate in the United States would be served well with an SAE 15W40 multi-viscosity diesel engine oil. The 15W viscosity grade part of this engine oil will effectively handle cold cranking start ups of -20 degrees C. The 40 SAE grade of this oil can handle and offer continuous operation up to 40 degrees C ambient temperatures. For those conditions where diesel engines will experience colder start up temperatures, choose a 10W30 multi-viscosity diesel engine oil. Such a lighter viscosity oil can provide a slight improvement in fuel economy. The lighter the oil, the less fluid friction, which translates to the engine expending less energy. It should be stated that this oil should only be used where the continuous operation in ambient temperatures does not go beyond 30 degrees C.

So far, we’ve discussed viscosities when dealing with operating temperature ranges for both start up and ambient temperatures during continuous use. Things become a bit more complicated when discussing a diesel engine oil’s performance. This area requires more careful thought and understanding when choosing the correct grade of oil for a specific diesel engine. Choosing the incorrect diesel motor oil for certain modern diesel engines can cause damage. Components such as exhaust treatment systems and diesel particulate filters could be damaged by using the incorrect diesel engine oil.

Diesel engine.
Diesel engine oils are required to deal with a myriad of issues happening inside the engine during operation. It must control piston ring cleanliness, acid neutralization, and avoid oxidation.









Engine oil grades for diesel engine applications have changed over time. In the years gone past covering the mid-1950s until the mid-1980s, the American Petroleum Institute (API) had two service classifications for diesel engine oil performance. Those two service classifications were either API CC or API CD. For non-turbo charged diesel engines, the typical choice would be to use the API CC engine oils. For turbo charged diesel engines, the most common engine oil was the API CD service classification. The proper motor oil for a Detroit Diesel two-cycle engine was based on the oil’s sulfated ash levels. During those prior years, an API CC typically met Detroit Diesel requirements.

As OEMs started to advance diesel engine development, there became a need for diesel engine oils to be higher performing in certain areas. There was more demands  placed on diesel engine oils to reduce piston top-land deposits, reduce oil system sludging, offer superior oil consumption reduction, and deliver improved piston ring belt cleanliness. The American Petroleum Institute instigated stricter diesel oil classifications from 1985 and beyond. These API classifications were CE, CF-4, CF-CF-2, and CG-4. These API service classifications were created so that diesel engine oils could cope with the demands for controlling valve train wear, deliver less high temperature piston deposits, offer superior thermal stability and oxidation resistance, and better control soot accumulation.

Bulldozer on the beach.
Diesel engine technology continues to advance and so does diesel engine oil technology. Diesel motor oils must control soot accumulation, protect valve trains from wear, and resist oxidation.








The API brought about the next phase of diesel engine service classifications that were needed because of increased environmental concerns and also the continued engine development by OEMs. This next phase of API diesel motor oil services classifications are as follows: CH-4, CI-4, CJ-4, and the newest CK-4. These classifications were developed because of the demands placed on the diesel engine oil from EGR (exhaust gas recirculation) and the catalyst systems that found their way into diesel engines from the early 2000s onward.

API CK-4, CJ-4, CI-4, and CH-4 series are backward compatible. This means that these service classifications could be used where older or lower classification oils are specified, such as an API CG-4.

Internal diesel engine.
Diesel engine motor oil API service classifications are in a continuous state of evolution, with the newest one called CK-4. API FA-4 has been released with an eye towards the future.









There is a new API service classification called API FA-4. This classification was specially created for diesel engines that most likely will be engineered from 2017 forward. FA-4 has a viscosity of SAE XW-30 solely for diesel engine oils. These API FA-4 diesel engine oils will be formulated to deal with greenhouse gas emissions. These oils must also be able to deal with the coming of highly engineered exhaust treatment systems planned for the future. This specific API service classification is not backward compatible nor interchangable with any previous API classifications. API FA-4 oils cannot replace or be used instead of API CK-4, CJ-4, CI-4, and CH-4 oils.

API service classifications were specifically created to deal with the lubrication requirements of North American diesel engines. Still, OEMs around the globe all typically specify API service classifications when providing requirements for diesel engine oils for their specific diesel engines.

Diesel semi truck.
OEMs worldwide utilize North America’s API service classifications, but also many diesel manufacturers create their own unique engine oil specification requirements.







The European Automobile Manufacturers Association (ACEA)  started providing engine oil specifications in the early 1990s. ACEA provides engine oil specifications for cars, light van petrol, and diesel engine oils, having a classification A/B. The engine oil specifications for high-performance cars, light van petrol, and diesel engine oils that need catalyst compatibility, use a classification C. Heavy duty diesel engine oils carry the classification E. ACEA engine oil classifications require motor oils to offer superior stay-in-grade viscosity performance. Also, they require more stringent exhaust treatment system compatibility. Some of the ACEA engine oil classifications are requiring oils to provide extended oil drain service and capabilities.

JASO stands for the Japanese Automotive Standards Organization. These service classifications require diesel engine oils to meet certain performance parameters such as valve train wear, piston cleanliness, high temperature oxidation resistance, and soot carrying ability. Certain specific tests done for these JASO classification are very specific to certain Japanese diesel engines. There are two JASO classifications currently used, which are for low ash formulations where diesel engines utilize after treatment devices, such as catalyst and DPFs (diesel particulate filters.) The classification JASO DH-2 was specifically designed for heavy duty diesel engines found in both buses and trucks. The classification JASO DL-1 is specifically for diesel engine powered passenger cars.

Diesel tractor.
When choosing the correct grade of diesel engine oil for your equipment, first check the owner’s manual, consult with the local equipment dealer, or check with the local engine oil supplier.









Many current diesel engine OEMs have come up with their own specific diesel engine oil specifications. Manufacturers such as Volvo, Cummings, Mercedes-Benz, Caterpillar, Renault, Detroit Diesel, Mack, and Deutz are just some of the diesel manufacturers. Certain OEMs have even specified a maximum level of Sulfated Ash/Sulfur/Phosphorous in their motor oils. These motor oils are often known as “low SAPS.”

The question arises, after all that has been discussed, which specific diesel engine oil should be utilized? It is important to remember that any motor oil is defined by its level of performance and its viscosity. First of all, it is critical to check your specific engine’s recommendation. Your owner’s manual should provide the required information. Current modern diesel engines will be specifying diesel motor oils that meet current modern service classifications. As an example, in your owner’s manual you may see listed API CJ-4 or, for European engines, ACEA E4/E6/E7/E9. The following manufacturer’s specification may also be found listed, such as Volvo VDS-4, MB-228.51, or CAT ECF-3. Maybe you might also see a SAPS specification. Older diesel engines may only require a diesel engine oil that meets API service classification CI-4, API CH-4, or even only CG-4. Depending on the ambient temperature operating range that the vehicle will have to deal with, choose the most appropriate viscosity grade.

If you are still unsure about the proper choice of engine oil grades for diesel engine operations, contact your local engine oil representative or distributor. They should be capable of specifying the correct engine oil for your fleet or vehicle. Depending on the variety of equipment in your fleet, you may need more than one specific diesel oil.