How to understand different engine oils?

If you want to know what to use for your car, follow what your vehicle manufacturer has stated. If you would like to better understand what all the gobble-de-gook means, continue reading ---

Oil

Originally there was crude oil. Black gold. Texas Tea. As crude oil, it is fairly much useless. It's the distillates which make up the usable parts. Crude oil is refined down to create lubricants and fuels through many different methods. This mainly happens by heating it and breaking it down into its usable components. Chemical engineers then take the oil and make it better. They will throw in additives to help it work better, to clean, and other such things we require of it. This type of oil is called regular oil or even "dino oil" (considering oil is considered to have originated from decomposing plants and animals which originated during the time of dinosaurs). When you look at a dino oil, it is not very consistent. When you consider an oil grade for dino oils, think of it as an average. I was once given this visualization of dino oil molecules:

.oOoo..oOOoOo...o.o.

Synthetic Oil

Synthetic oil is man made. Chemical engineers take base oil stock and chemically modify it to create a lubricant which is more stable than dino oil, where operating extremes (such as high performance autos or jet engines) occur. This oil is tailored to have a controlled molecular structure with predictable properties. There are many different types of synthetic oils, made many different ways. In line with the above visualization of dino oil molecules, synthetic oil molecules might look more like this:

ooooooooooooooooo

To this end, there are three different categories of oil products:

• Organic oil - Dino oil. Regular oil. Crude oil which has been boiled.
• Semi-Synthetic - A mix of dino oil and synthetic oil. Can also be called synthetic blend or semi-synthetic.
• Synthetic - Pure man-made oil (no dino oil added).

Oil Standards

There are several standards in the world which pertain to oil. Some of those standards are from the:

• Society of Automotive Engineers (SAE)
• European Automobile Manufacturers Association (ACEA)
• American Petroleum Institute (API)

(NOTE: These are some main ones, but there are others). To better understand what each organization's, let's break some things down for you.

Each organization has a different indicator for their oil specification. Here are the indicators for each of the three major organizations:

• SAE - 0W, 5W, 10W, 20W, 25w, 8**, 12**, 16**, 20, 30, 40, 50, 60 (NOTE: ** New SAE Standard)
• ACEA - A1/B1, A3/B3, A3/B4, A5/B5, C1, C2, C3, C4, E4, E6, E7, D9
• API - GF-6B, GF-6A, SP, SN, SM, SL, SJ, SH, SG, SF, SE, SD, SC, SB, SA, CJ-4, CI-4 Plus, CI-4, CH-4, CG-4, CF-2, CF, CF-4, CE, CD-II, CD, CC, CB, CA

This is called the API Donut. It has two of these three service ratings listed in them and also tells whether an oil is considered "Energy Conserving":

NOTE1: These standards can best be understood by reading through the standards body write-ups, but I will try to give a brief overview of what is important, as well as some charts which will describe them a little better than I can with a wall-of-words in this article.

NOTE2: This write-up is for motor oil. Do not confuse this with how gear or other oil is labeled, because it has a completely different standard, though some of the markings appear in the same configuration.

I'll start with SAE because it is probably the most confusing.

SAE

All of SAE specifications have to do with the viscosity of an oil. The viscosity meaning, what is the specific flow rate, at a specific temperature, through a specific sized orifice. There are two basic types of oil concerned when you are looking at the SAE specification. There is straight weight and multi-viscosity. Straight weight oil does not contain modifiers which affect how the oil flows. It is denoted by a single number such as 30. A multi-viscosity will have different flow properties depending on the temperature. It is denoted by a hyphenated number, such as 0W-20.

NOTE3: Do not think of oil viscosity numbers in terms of thicker or thinner ... Flow rate is modified by means other than the how thick or thin it is.

The first number of the two has a "W" following it. This indicates the Winter or cold start viscosity of the oil (though some mistakenly think the "W" stands for "weight"). Originally this denoted the viscosity of oil when it is measured at 0degF. In 1999 this was changed due to an outbreak of engine failure due to oil jelling at low temperatures (see chart below for newer standard). The second number denotes the viscosity of the oil when measured at 100degC (or 212degF).

This chart indicates some numbers which may or may not be useful to the average Joe, but are the specification for each of the numbers I've listed (other than 8**, 12**, & 16** which are newer SAE oil specifications):

You will notice that the for each of the Winter designations, it is mainly concerned with how well the oil flows at a given minimum temperature. Whereas the straight number has concerns on both the minimum and maximum flow rate of an oil.

NOTE4: 100degC (or 212degF) is used as a main reference point due to this being the approximate running temperature of an engine. It is an easy reference point to work with.

NOTE5: Please understand that a 5W-30 and 10W-30 are still 30 grade oils and will still perform the same at a higher given temperature. The difference is their flow rate is different at the lower temperatures. This is achieved through molecular chains which open (become straight) and close (bunch up) at different temperatures. This opening and closing effect changes how the oil flows and thus effectively changes the viscosity without changing the oil grade itself.

Here is a general chart of which oil should be used in which temperature range (though it is my personal belief you should follow what your vehicle manufacturer's recommendation so as to not void warranties, etc):

Some vehicle manufacturers will give you a variance chart in your owner's manual which tells you which weight to use if you sustain higher or lower temperatures during the year.

ACEA

The ACEA is a little easier to figure out than SAE. Their standards are broken down into three main areas: A/B; C; and E.

• A/B: Gasoline (petrol) and Diesel Engine Oils
• C: Catalyst Compatibility Oils
• E: Heavy Duty Diesel Engine Oils

Here is the write-up I pulled from this website which explains each of the individual specifications. Each of the following is a current specification:

A1/B1 Stable, stay-in-grade oil intended for use at extended drain intervals in gasoline engines and car & light van diesel engines specifically designed to be capable of using low friction low viscosity oils with a high temperature / high shear rate viscosity of 2.6 mPa*s for xW/20 and 2.9 to 3.5 mPa.s for all other viscosity grades. These oils are unsuitable for use in some engines. Consult owner manual or handbook if in doubt.

A3/B3 Stable, stay-in-grade oil intended for use in high performance gasoline engines and car & light van diesel engines and/or for extended drain intervals where specified by the engine manufacturer, and/or for year-round use of low viscosity oils, and/or for severe operating conditions as defined by the engine manufacturer.

A3/B4 Stable, stay-in-grade oil intended for use in high performance gasoline and direct injection diesel engines, but also suitable for applications described under A3/B3.

A5/B5 Stable, stay-in-grade oil intended for use at extended drain intervals in high performance gasoline engines and car & light van diesel engines designed to be capable of using low friction low viscosity oils with a High temperature / High shear rate (HTHS) viscosity of 2.9 to 3.5 mPa.s. These oils are unsuitable for use in some engines. Consult owner manual or handbook if in doubt.

C1 Stable, stay-in-grade oil intended for use as catalyst compatible oil in vehicles with DPF and TWC in high performance car and light van diesel and gasoline engines requiring low friction, low viscosity, low SAPS oils with a minimum HTHS viscosity of 2.9 mPa.s. These oils will increase the DPF and TWC life and maintain the vehicles fuel economy. Warning: these oils have the lowest SAPS limits and are unsuitable for use in some engines. Consult owner manual or handbook if in doubt.

C2 Stable, stay-in-grade oil intended for use as catalyst compatible oil in vehicles with DPF and TWC in high performance car and light van diesel and gasoline engines designed to be capable of using low friction, low viscosity oils with a minimum HTHS viscosity of 2.9mPa.s. These oils will increase the DPF and TWC life and maintain the vehicles fuel economy. Warning: these oils are unsuitable for use in some engines. Consult owner manual or handbook if in doubt.

C3 Stable, stay-in-grade oil intended for use as catalyst compatible oil in vehicles with DPF and TWC in high performance car and light van diesel and gasoline engines, with a minimum HTHS viscosity of 3.5mPa.s. These oils will increase the DPF and TWC life. Warning: these oils are unsuitable for use in some engines. Consult owner manual or handbook if in doubt.

C4 Stable, stay-in-grade oil intended for use as catalyst compatible oil in vehicles with DPF and TWC in high performance car and light van diesel and gasoline engines requiring low SAPS oil with a minimum HTHS viscosity of 3.5mPa.s. These oils will increase the DPF and TWC life. Warning: these oils are unsuitable for use in some engines. Consult owner manual or handbook if in doubt.

C5 Stable, stay-in-grade Engine Oil with Mid SAPS-Level, for further improved Fuel Economy, intended for use as catalyst compatible Oil at extended Drain Intervals in Vehicles with all Types of modern Aftertreatment Systems and High Performance Passenger Car & Light Duty Van Gasoline & DI Diesel Engines that are designed to be capable and OEM-approved for use of Low Viscosity Oils with a minimum HTHS Viscosity of 2.6 mPa.s.

E4 Stable, stay-in-grade oil providing excellent control of piston cleanliness, wear, soot handling and lubricant stability. It is recommended for highly rated diesel engines meeting Euro I, Euro II, Euro III, Euro IV and Euro V emission requirements and running under very severe conditions, e.g. significantly extended oil drain intervals according to the manufacturer's recommendations. It is suitable for engines without particulate filters, and for some EGR engines and some engines fitted with SCR NOx reduction systems. However, recommendations may differ between engine manufacturers so Driver Manuals and/or Dealers shall be consulted if in doubt.

E6 Stable, stay-in-grade oil providing excellent control of piston cleanliness, wear, soot handling and lubricant stability. It is recommended for highly rated diesel engines meeting Euro I, Euro II, Euro III, Euro IV and Euro V emission requirements and running under very severe conditions, e.g. significantly extended oil drain intervals according to the manufacturer's recommendations. It is suitable for EGR engines, with or without particulate filters, and for engines fitted with SCR NOx reduction systems. E6 quality is strongly recommended for engines fitted with particulate filters and is designed for use in combination with low sulphur diesel fuel. However, recommendations may differ between engine manufacturers so Driver Manuals and/or Dealers shall be consulted if in doubt.

E7 Stable, stay-in-grade oil providing effective control with respect to piston cleanliness and bore polishing. It further provides excellent wear control, soot handling and lubricant stability. It is recommended for highly rated diesel engines meeting Euro I, Euro II, Euro III, Euro IV and Euro V emission requirements and running under severe conditions, e.g. extended oil drain intervals according to the manufacturer's recommendations. It is suitable for engines without particulate filters, and for most EGR engines and most engines fitted with SCR NOx reduction systems. However, recommendations may differ between engine manufacturers so Driver Manuals and/or Dealers shall be consulted if in doubt.

E9 Stable, stay-in-grade oil providing effective control with respect to piston cleanliness and bore polishing. It further provides excellent wear control, soot handling and lubricant stability. It is recommended for highly rated diesel engines meeting Euro I, Euro II, Euro III, Euro IV and Euro V emission requirements and running under severe conditions, e.g. extended oil drain intervals according to the manufacturer's recommendations. It is suitable for engines with or without particulate filters, and for most EGR engines and for most engines fitted with SCR NOx reduction systems. E9 is strongly recommended for engines fitted with particulate filters and is designed for use in combination with low sulphur diesel fuel. However, recommendations may differ between engine manufacturers so Drivers Manuals and/or Dealers should be consulted if in doubt.

And finally ...

API

The API has two distinct categories. Those for gasoline engines (S designation) and for diesel engines (C designation). I am only going to give you the write-ups for those specifications which are current. You can look where I pulled them from to get the rest if you are so inclined:

GF-6A Introduced in May 2020 designed to provide protection against low-speed pre-ignition (LSPI), timing chain wear protection, improved high temperature deposit protection for pistons and turbochargers, more stringent sludge and varnish control, improved fuel economy, enhanced emission control system protection and protection of engines operating on ethanol-containing fuels up to E85.

GF-6B *Introduced in May 2020, applies only to oils having an SAE viscosity grade of 0W-16, designed to provide protection against low-speed pre-ignition (LSPI), timing chain wear protection, high temperature deposit protection for pistons and turbochargers, stringent sludge and varnish control, improved fuel economy, emission control system protection and protection of engines operating on ethanol-containing fuels up to E85.

SP Introduced in May 2020 designed to provide protection against low-speed pre-ignition (LSPI), timing chain wear protection, improved high temperature deposit protection for pistons and turbochargers, and more stringent sludge and varnish control. API SP with Resource Conserving matches ILSAC GF-6A by combining API SP performance with improved fuel economy, emission control system protection and protection of engines operating on ethanol-containing fuels up to E85.

SN Introduced in October 2010 Introduced in October 2010 for 2011 and older vehicles, designed to provide improved high temperature deposit protection for pistons, more stringent sludge control, and seal compatibility. API SN with Resource Conservingmatches ILSAC GF-5 by combining API SN performance with improved fuel economy, turbocharger protection, emission control systemcompatibility, and protection of engines operating on ethanol-containing fuels up to E85.

SM Introduced on 30 November 2004 Category SM oils are designed to provide improved oxidation resistance, improved deposit protection, better wear protection, and better low-temperature performance over the life of the oil. Some SM oils may also meet the latest ILSAC specification and/or qualify as Energy Conserving. They may be used where API Service Category SJ and SL earlier categories are recommended.

SL 2001 Gasoline Engine Service Category SL was adopted to describe engine oils for use in 2001. It is for use in service typical of gasoline engines in present and earlier passenger cars, sports utility vehicles, vans and light trucks operating under vehicle manufacturers recommended maintenance procedures. Oils meeting API SL requirements have been tested according to the American Chemistry Council (ACC) Product Approval Code of Practice and may utilize the API Base Oil Interchange and Viscosity Grade Engine Testing Guidelines. They may be used where API Service Category SJ and earlier categories are recommended.

SJ 1997 Gasoline Engine Service Category SJ was adopted in 1996 to describe engine oil first mandated in 1997. It is for use in service typical of gasoline engines in present and earlier passenger cars, vans, and light trucks operating under manufacturers recommended maintenance procedures. Oils meeting API SH requirements have been tested according to the American Chemistry Council (ACC) Product Approval Code of Practice and may utilize the API Base Oil Interchange and Viscosity Grade Engine Testing Guidelines. They may be used where API Service Category SH and earlier categories are recommended.

FA-4 API Service Category FA-4 describes certain XW-30 oils specifically formulated for use in select high-speed four-stroke cycle diesel engines designed to meet 2017 model year on-highway greenhouse gas (GHG) emission standards. These oils are formulated for use in on-highway applications with diesel fuel sulfur content up to 15 ppm (0.0015% by weight). Refer to individual engine manufacturer recommendations regarding compatibility with API FA-4 oils. These oils are blended to a high temperature high shear (HTHS) viscosity range of 2.9cP–3.2cP to assist in reducing GHG emissions. These oils are especially effective at sustaining emission control system durability where particulate filters and other advanced aftertreatment systems are used. API FA-4 oils are designed to provide enhanced protection against oil oxidation, viscosity loss due to shear, and oil aeration as well as protection against catalyst poisoning, particulate filter blocking, engine wear, piston deposits, degradation of low- and high-temperature properties, and soot-related viscosity increase. API FA-4 oils are not interchangeable or backward compatible with API CK-4, CJ-4, CI-4 with CI-4 PLUS, CI-4, and CH-4 oils. Refer to engine manufacturer recommendations to determine if API FA-4 oils are suitable for use. API FA-4 oils are not recommended for use with fuels having greater than 15 ppm sulfur. For fuels with sulfur content greater than 15 ppm, refer to engine manufacturer recommendations.

CK-4 Current - 2017 API Service Category CK-4 describes oils for use in high-speed four-stroke cycle diesel engines designed to meet 2017 model year on-highway and Tier 4 non-road exhaust emission standards as well as for previous model year diesel engines. These oils are formulated for use in all applications with diesel fuels ranging in sulfur content up to 500 ppm (0.05% by weight). However, the use of these oils with greater than 15 ppm (0.0015% by weight) sulfur fuel may impact exhaust aftertreatment system durability and/or oil drain interval. These oils are especially effective at sustaining emission control system durability where particulate filters and other advanced aftertreatment systems are used. API CK-4 oils are designed to provide enhanced protection against oil oxidation, viscosity loss due to shear, and oil aeration as well as protection against catalyst poisoning, particulate filter blocking, engine wear, piston deposits, degradation of low- and high-temperature properties, and soot-related viscosity increase. API CK-4 oils exceed the performance criteria of API CJ-4, CI-4 with CI-4 PLUS, CI-4, and CH-4 and can effectively lubricate engines calling for those API Service Categories. When using CK-4 oil with higher than 15 ppm sulfur fuel, consult the engine manufacturer for service interval recommendations.

CJ-4 Current - 2006 Introduced in 2006 for high-speed four-stroke engines. Designed to meet 2007 on-highway exhaust emission standards. CJ-4 oils are compounded for use in all applications with diesel fuels ranging in sulphur content up to 500ppm (0.05% by weight). However, use of these oils with greater than 15ppm sulfur fuel may impact exhaust after treatment system durability and/or oil drain intervals. CJ-4 oils are effective at sustaining emission control system durability where particulate filters and other advanced after treatment systems are used. CJ-4 oils exceed the performance criteria of CF-4, C-4, AH-4 and C-4.

CI-4 Plus Current - 2004 Used in conjunction with API C-4, the " CI-4 PLUS" designation identifies oils formulated to provide a higher level of protection against soot-related viscosity increase and viscosity loss due to shear in diesel engines. Like Energy Conserving, CI-4 PLUS appears in the lower portion of the API Service Symbol "Donut."

CI-4 Severe-Duty Diesel Engine Service The CI-4 performance requirements describe oils for use in those high speed, four-stroke cycle diesel engines designed to meet 2004 exhaust emission standards, to be implemented October 2002. These oils are compounded for use in all applications with diesel fuels ranging in sulfur content up to 0.05% by weight. These oils are especially effective at sustaining engine durability where Exhaust Gas Recirculation (EGR) and other exhaust emission componentry may be used. Optimum protection is provided for control of corrosive wear tendencies, low and high temperature stability, soot handling properties, piston deposit control, valve train wear, oxidative thickening, foaming and viscosity loss due to shear. CI-4 oils are superior in performance to those meeting API CH-4, CG-4 and CF-4 and can effectively lubricate engines calling for those API Service Categories.

CH-4 Severe-Duty Diesel Engine Service This service oils are suitable for high speed, four-stroke diesel engines designed to meet 1998 exhaust emission standards and are specifically compounded for use with diesel fuels ranging in sulfur content up to 0.5% weight. CH-4 oils are superior in performance to those meeting API CF-4 and API CG-4 and can effectively lubricate engines calling for those API Service Categories.

NOTE6: A lot of this data you will never need to know. I have placed it here for future reference. I can see this being updated over time as new standards are brought to bear.