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ENGINE OIL SAE VISCOSITY CLASSIFICATION & MANUFACTURERS REQUIREMENTS and API Service Classifications

The SAE is the Society of Automotive Engineers. The SAE classifies motor oils according to certain viscosities and very general temperature ranges at which they can be used.  Automobile and equipment manufacturers also specify which oil should be used for a particular ambient temperature operation. It is important to note that the viscosity and temperature range values listed by automobile and equipment manufacturers are almost always meant for petroleum oil.  The same viscosity oil in a premium quality synthetic will have drastically lower cold temperature flow and operation properties as well as drastically higher high temperature operational properties. This is very important to remember this when determining which oil to use in a specific application and ambient temperature or range of temperatures expected to be encountered. 

Today, most automobiles and trucks use multi-viscosity oils. Multi-viscosity petroleum oils are manufactured by starting with a lower viscosity base stock oil and blending in Viscosity Index Improvers (VI's).   The purpose of the VI's are to allow a lower viscosity oil, such as a SAE 10W oil to flow like a 10W oil at low ambient temperatures (such as during cold starting) and also flow like a SAE 30W oil at higher ambient and operating temperatures. The resultant formulation is called a multi-viscosity oil, and in this example, would be called a SAE 10W-30. 

There are certain applications that a multi-viscosity petroleum oil is not optimum for and will be listed below due to the critical importance that you understand this concept.  Applications such as high RPM, high load small engines such as lawn mowers usually are specified to use a SAE 30W petroleum oil, although the owners manual never specifically states petroleum oil. Some high horsepower racing or diesel engines also may be recommended to use a SAE 30W or SAE 40W petroleum oil by a particular engine manufacturer or builder. 

The problem that can occur in petroleum based motor oils with VI's is that under heat, load and shear forces the molecules of the VI tend to change shape from a round shaped molecular structure to a straightened, or aligned, molecular structure. When this occurs the VI's are subject to degradation due to shear forces created inside the engine, which can cause a temporary loss of the oils specified viscosity.  Under shear loads the molecules in the VI's align themselves in the direction of the shear stresses so there is less resistance to flow. As the oil cools and the shear forces are no longer present the VI's return to their original molecular configuration and the original viscosity is returned to the oil.   Where serious problems can occur are under extreme heat and shear loads where the molecular structure of the VI's are permanently destroyed and will not return to their original configuration when the oil cools and shear stresses are no longer present.   This is the prime reason that, as discussed previously, small engine manufacturers and certain specific diesel engine manufacturers specify a straight weight petroleum oil with no VI's. 

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WHAT ABOUT ENGINES THAT REQUIRE A STRAIGHT WEIGHT OIL? 

While we are on the subject of oil shearing I though it appropriate to discuss this topic. I get many calls asking why manufacturers of small engines, such as used in lawn mowers, generators and even some larger diesel engines or racing engines require either a SAE 30 or SAE 40 oil. The reason, as stated previously, is that first and foremost, they are referring to a petroleum motor oil. 

These types of engines operate under extreme RPM, load and heat and in the case of small engines are mainly air-cooled.  Multi-viscosity petroleum oils are full of viscosity improvers, VI's. It is these viscosity improvers that are the weak link. As these agents are subjected to heat, load and high RPM the oil cannot reach its intended high temperature viscosity, which results in shearing. As this shearing continues the results can be loss of oil film strength, increased wear rates and temperatures and oil consumption issues. That is the reason straight weight petroleum oils are recommended for these types of applications. 

When a premium quality multi-viscosity synthetic oil, such as a 10W-30, 10W-40 or 15W-40 oil is used these concerns are non-existent. Synthetic oil is incredibly shear resistant. The bottom line is that the manufacturers specifications are based on petroleum oils, yet your owners manual is not going to explain that, so you in turn go out looking for the required straight weight petroleum oil.  You would be much better off using a premium quality synthetic oil in these type of applications.

The problem is that, although synthetic oils are becoming much more widespread in use, almost all automobile and equipment owners manuals are written in reference to petroleum oil viscosities and specifications yet they do not specifically state this. If the specifications and recommendations were changed to include synthetic oil there would be no need to have 4 or 5 different viscosity oils listed, for example, for different ambient operating temperature conditions. One multi-viscosity synthetic oil would cover everything from extreme cold to extreme heat. 

Automobile and equipment manufacturers in the U.S. are slowly coming around as they realize more and more of their customers will change to synthetic lubricants.  Some automobile manufacturers use synthetic oil as a factory fill on specific high performance models. Others only use synthetics where it is needed to solve a problem, typically heat or wear related.

The API is the American Petroleum Institute. The API maintains a system of Service Classifications  (API ratings) for gasoline engines and Commercial Classifications (CC ratings) for diesel engines.  The procedures, procedures and policies by which lubricants are rated is a constantly changing system and involves representatives from the major automotive companies, API, oil manufacturers other engineering activities. Periodically changes are made to the specifications to keep up to date with current gasoline and diesel engine technology.   

There are many classifications that have become obsolete and are no longer used. For example, occasionally I receive calls from people that have purchased a new piece of equipment stating they have to use an SE oil.  I explain to them that SE oil specifications began in 1971 and were obsolete with the new SF specifications released in 1981. Today both SE and SF are obsolete. What has most likely happened is that some technical editor or clerk has transcribed portions of a previous service or owners manual to the new manual without completely reviewing it for any errors or updates to specifications. 

The specifications referred to in these classifications generally have to do with oxidation protection, high temperature engine deposits, foaming, acid formation, sludge control and rust and corrosion protection. I have listed only the most recent classifications. There are many obsolete specifications that will not be covered in this book. These specifications are constantly changing and are subject to change as new engine, emissions and vehicles and/or government requirements arise. Note that when a new specification is released it makes the previous specification obsolete, therefore when an applications specifies the obsolete lubricant you may use the lubricant with the API classification that has superceded and replaced it

API SERVICE CLASSIFICATIONS FOR GASOLINE ENGINES  

SH- For 1994-1996 Gasoline Engine Service  (Obsolete)

Classification SH was adopted in 1992 and recommended for gasoline engines in passenger cars and light trucks starting in 1993 model year. This category supercedes the performance requirements of API SG specification for 1989-1992 models, which is now obsolete. Applications that call for an API service classification SG can use the SH specification.  The specification addresses issues with deposit control, oxidation, corrosion, rust and wear and replaces.

SJ- For 1997-2001 Gasoline Engine Service (Current Spec.)

Classification SJ was adopted in 1996 and recommended for gasoline engines in passenger cars and light trucks starting in 1997 model year. Applications specifying API SH can use the newer API SJ service classification.  Note that where applicable certain letters in the sequence will be skipped to prevent confusion with other standards. In this case, SI was skipped since industrial oils are currently rated according to SI classifications. 

SL- For 2001-2004 Gasoline Engine Service- (Current Spec.)

Recommended for gasoline engines in passenger cars and light trucks starting in July 2001. SL oils are engineered to provide improved high temperature deposit control and lower oil consumption. Applications specifying API SJ can use the new API SL service classification. Note that some SL rated oils may also meet the latest ILSAC specification and/or qualify as energy conserving. SL is the latest specification.

SM- For 2004 and newer Gasoline Engine Service Automotive Engines (Current Spec)

This specification was introduced in Nov. 2004. SM oils are engineered to provide improved oxidation resistance, improved deposit and wear protection and improved low temperature performance. Note that some SM rated motor oils may also meet the current ILSAC specification.

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CC- COMMERCIAL CLASSIFICATIONS FOR DIESEL ENGINES

CF-For 1994 Off-Road Indirect Injected Diesel Engine Service 

API Service Category CF denotes service typical of off-road, indirect injected diesel engines and other diesel engines that use a broad range of fuel types, including those using fuel with higher sulfur content (over 0.5% wt sulfur fuel).  Effective control of piston deposits, wear and corrosion of copper-containing bearings is essential for these engines, which may be naturally aspirated, turbocharged or supercharged.  Oils designated for this service may also be used when API Service Category CD or CE is recommended. CF is a current specification. 

CF-2- FOR 1994 Severe Duty 2-Stroke Cycle Diesel Engine Service 

API Service Category CF-2 denotes service typical of two-stroke cycle engines (such as Detroit Diesel) requiring highly effective control over cylinder and ring-face scuffing and deposits.  Oils designated for this service have been in existence since 1994 and may also be used when API Service Category CD-II is recommended.  These oils do not necessarily meet the requirements of CF or CF-4, unless they pass the test and performance requirements for these categories. CF-2 is a current specification.

CF-4- For 1990 Diesel Engine Service 

Service typical of severe duty turbocharged, 4-stroke cycle diesel engines, particularly late models designed to give lower emissions.  These engines are usually found in on-highway, heavy-duty truck applications.  API CF-4 oils exceed the requirement of CE category oils and can be used in place of earlier CC, CD and CE oils. CF-4 oils provide for improved control of piston deposits and oil consumption. 

The CF-4 classification meets Caterpillar engine requirements, as well as earlier Mack Trucks (T-6 & T-7) and Cummins (NTC-400) multi-cylinder engine test criteria. When combined with the appropriate category, they can be used in gasoline and diesel powered cars and light trucks as specified by the vehicle and/or engine manufacturer. 

CG-4- For 1995 Severe Duty Diesel Engine Service 

API Service Category CG-4 describes oils for use in high speed, four-stroke cycle diesel engines used in highway and off-road applications, where the fuel sulfur content may vary from less than 0.05% by weight to less than 0.5% by weight.  CG-4 oils provide effective control over high temperature piston deposits, wear, corrosion, foaming, oxidation stability and soot accumulation.  These oils are especially effective in engines designed to meet 1994 exhaust emissions standards and may also be used in engines requiring API Service Categories CD, CE and CF-4.  Oils designated for this service have been in existence since 1995. CG-4 is a current specification 

CH-4- For 1999 Severe Duty Diesel Engine Service 

API Service Category CH-4 describes oils for use in high speed, four-stroke cycle diesel engines used in highway and off-road applications.  CH-4 oils provide effective control over engine deposits, wear, corrosion, oxidation stability and soot accumulation.  These oils are especially effective in engines designed to meet 1999 emission standards and may also be used in engines requiring API Service Category CG-4.  Oils designated for this service have been in existence since 1999. CH-4 oils are engineered for use with diesel fuels ranging in sulfur content up to 0.5% weight.  CH-4 is a current specification. 

CL-4- For 2002 Severe Duty Diesel Engine Service 

API Service Category CL-4 describes oils for use in those high speed, four-stroke cycle diesel engines designed to meet 2004 exhaust emissions standards and was implemented in October 2002.  These oils are engineered for all applications where diesel fuel sulfur content is up to 0.05% by weight.  These oils are very effective at sustaining engine durability where EGR ( Exhaust Gas Recirculation) and other exhaust emissions systems are used and provide for optimum protection in the areas of corrosive wear, low and high temperature stability, soot handling properties, piston deposit control, valvetrain wear, oxidative thickening and foaming and viscosity loss due to shear.  API CL-4 oils are superior in performance to those meeting API-CH-4, CG-4 and CF-4 and can be used and will effectively lubricate diesel engines specifying those API service Classifications    

See Changes in the Diesel Market, new CJ-4 Emission Compliant Diesel Oil  For 2007 and Newer Diesel Engines  

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Manufacturer Specific Diesel Pickup Truck Pages:

Ford Powerstroke

Duramax Diesel

Dodge Cummins       

COMBINED API SERVICE CLASSIFICATIONS  

Most motor oils are currently available in combined API Service Classifications. The combined classification is a high quality oil that is formulated with the proper base stocks and additive package to provide protection for both turbocharged gasoline and diesel powered engines in severe service applications. 

Combined API Service Classification motor oils are highly effective at reducing and controlling sludge and varnish deposits, acid and foam formation and have improved oxidation stability.  An example of a combined API Service Classification is API SH/CG-4.

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