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API Specification? This is how it works!

The American Petroleum Institute, API, is a U.S.A trade association for the oil and natural gas industry. It reunites different actors in the production, refinement, distribution and many other activities around petroleum. Amongst their activities, they set up diverse technical standards, such as measurement methods, standards for the design of pressure vessels, etc., but also industry standard for the energy conservation of the motor oil.

There are two categories: gasoline and diesel. Category S is for “Spark Ignition”, for Gasoline and category C is for “Compression Ignition’, for Diesel. For both, the letter S or C is followed by another letter. For example, SM or CF. The higher the letter, the more recent the technology of the oil. For recent oil, the higher specification will supersede the lower letter grade. For example, if we have an oil with specification SN, it can also be used for vehicles which request API SM, SL and SJ; it is backward compatible.

However, you have to pay attention to the year of construction of the engine. If the engine is too old, modern chemistry might not be adapted or compatible with old engine designs and materials used to make the engine. Let’s see by category how it works.

Gasoline (or Petrol) Engine Service Classifications

Below are all the API categories in Gasoline. It is mainly for passenger car, as most of the cars in US are Gasoline and not Diesel.

Specifications from SA to SH are considered obsolete, meaning that you cannot get any official license from the API. It is meant for 1995 and older engines. As explained earlier, the higher the letter, the more recent and a higher specification would supersede the lower ones. API SN to SJ are for the most recent cars, API SH to SA for the older cars. Few examples to illustrate what would be the best:

  • Example 1: Car from 1987 and you only have two available oils, one with API SH, the other one with SL. If you read the table properly, the car needs an API SF. In theory, both SH and SL could be used. As also explained earlier, more modern oils are not necessarily adapted for older engines. Therefore, the oil with SH level would be more adapted.
  • Example 2: Car from 2003 and you have different oils available: API SJ, SM or SN. In this case, you need API SL, so an API SJ, lower, cannot be good. SM and SN supersedes SL so both oils can be used.

Generally speaking, the best would be to follow the recommendation of the table.

If you want to have more details about API and their lubricant program, check there website.

Diesel Engine Service Classifications

In December 2016, the American Petroleum Institute (API) issued their new heavy duty Diesel specifications, 10 years after the issue of API CJ-4.

The main drivers for change of specifications are boosting fuel economy while maintaining durability of the engine running at hotter temperatures. The trend of fuel economy comes from the end-used striving for lower operation costs but also from more and more restricted green house gas (GHG) emissions regulation. Back in 2011, Environmental Protection Agency (EPA), with other American agencies, set up a new Heavy Duty National Program to establish new rules to reduce the GHG emissions and reduce fuel consumption. In order to fulfill these new requirements, new engine designs had to be introduced and started to look at lower viscosity lubricants to enhance the fuel economy. Engine Manufacturer Association (EMA) made a formal request to the API for a new commercial engine oil category. Before a final name could be decided, the new category has been called Proposed Category 11, PC-11.

PC-11 specification ends the easiness of API. Indeed, when a new specification is issued, it is then backward compatible with the older ones. For example, if a vehicle request a CH-4 and there is only lubricant with API CJ-4 available, it can be used. The new specifications PC-11 will divided in two categories:

  • 11- a: API CK-4, which is the direct replacement of CJ-4.
  • 11-b: complete new category, called FA-4

Both categories have enhanced durability and provide better Fuel economy compare to CJ-4.

CK-4 is designed to be a more robust CJ-4 with viscosity grades such as 15W/40, 10W/30 and 5W/40 and high HTHS. CK-4 oils will be recommended by every OEM for on and off-road applications.

FA-4 would be more a robust CJ-4 at lower viscosity. They will be mainly 10W30 and 5W30 grades, with low HTHS. These oils, though with a lower viscosity, are designed to fulfil the constraining durability requirements. They are designed only for on-road applications and will have to be used only where they are recommended by OEMs.

As a consequence, OEM are starting to issue new specifications for API CK-4 and/or API FA-4.

For more information, give us a call and we will be happy to explain you more: +31 (0) 316 74 08 56
Or, visit our product page to see which API products we offer.

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