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Can a cheap oil provide all the protection required?

Why is engine oil so much more expensive than other oils?

How are oils regulated or compared in the industry?

What are these categories?

Service Oils aka Spark Ignition Oils:

Commercial Oils aka Compression Ignition Oils:

API ratings for Gear Oils

Where can I find the API rating?

Other Ratings – ACEA

JASO

Can a cheap oil provide all the protection required?

To a degree, but for the superior performance required for more demanding applications a better base stock and more sophisticated additive package are required.

Why is engine oil so much more expensive than other oils?

Mainly because the oil is subject to extreme conditions in an engine compared to other mechanical systems such as gearboxes, axles or brakes, and so requires a better base stock and additive package.  These extreme conditions include:

  • High temperature leading to reduced oil service life as a result of increased oxidation activity.
  • High levels of contamination from the atmosphere, fuel/combustion and wear debris in that order.
  • Many moving (sliding and rolling) parts resulting in varying forms of lubrication from boundary lubrication to thick film, in addition to varying metals and varying load conditions all contributing to a more stressful environment for the oil.

This is why the oil is not only more expensive, but generally will not last as long as say a gearbox or hydraulic oils.  The additive package can form up to 30% of the volume of engine oil compared to just 1-10% of other oils. 

There is also the issue that pricing is set based on the fact that car enthusiasts are sometimes willing to pay a little extra.   The marketing of the engine oil products is very emotional with little hard science in evidence at times – the old adage that bull baffles brains applies quite frequently, not helped by incorrect “facts” continually trotted out across the internet in various forums.

How are oils regulated or compared in the industry?

The American Petroleum Institute (API) categorises the formulation of oils according to a standard.  Typical engines of the period are used as a test bed, and a number of tests are run to ascertain the performance of oil under test.  If it meets or exceeds the parameters of the test then it can be classified in that category.  However, oils in the same category do not necessarily have equal performance, they may only meet, not exceed, the requirements of that category.  Current ratings are based around standard engine design at the time, so modern oils are designed to withstand higher power outputs, with multi-valve and overhead cam etc reaching higher rpm than previously.  This does NOT necessarily mean they are unsuitable for older engines although this is a general guide in terms of selecting oils.

What are these categories?

For petrol or Spark Ignition engines, there is a ‘S’ rating, in which stands for Service.  For diesel or Compression Ignition engines, there is a ‘C’ rating, in which C stands for Commercial.

Service Oils aka Spark Ignition Oils:

The ratings started with an API SA rating, and this oil is not recommended for any vehicle in my opinion except vintage vehicles.  By the 70’s it had moved onto an API SC rating.  During the Nineties it rapidly moved up to as high API SJ, and is currently at SM.  The oil required will depend on your driving needs, i.e. daily commuting versus track-day or motorsport driving.  For the latter, buy the best you can afford, but for commuting, an API SL or API SJ should be more than adequate on modern cars unless SM is specified by the manufacturer. 

Service Ratings – Gasoline/Petrol/Spark Ignition Engines

Category

Status

Service

SM

Current

For all automotive engines currently in use.  Introduced in 2004, SM oils are designed to provide improved oxidation resistance, 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.

SL

Current

For 2004 and older automotive engines.

SJ

Current

For 2001 and older automotive engines.

SH

Obsolete

For 1996 and older engines.

SG

Obsolete

For 1993 and older engines.

SF

Obsolete

For 1988 and older engines.

SE

Obsolete

CAUTION: Not suitable for use in gasoline-powered automotive engines built after 1979.

SD

Obsolete

CAUTION: Not suitable for use in gasoline-powered automotive engines built after 1971.  Use in more modern engines may cause unsatisfactory performance or equipment harm.

SC

Obsolete

CAUTION: Not suitable for use in gasoline-powered automotive engines built after 1967.  Use in more modern engines may cause unsatisfactory performance or equipment harm.

SB

Obsolete

CAUTION: Not suitable for use in gasoline-powered automotive engines built after 1951.  Use in more modern engines may cause unsatisfactory performance or equipment harm.

SA

Obsolete

CAUTION:  Contains no additives. Not suitable for use in gasoline-powered automotive engines built after 1930.  Use in more modern engines may cause unsatisfactory performance or equipment harm.

 Table 6 – API Service Oil ratings  

Commercial Oils aka Compression Ignition Oils:

The API classification is currently at API CJ-4, although this is designed for exhaust gas recirculating (EGR) engines where the soot loading is consequently higher as a result of remixing the unburnt fuel and exhaust emissions into the air intake.  Again, the rating has moved on rapidly during the 90’s, and the same comment applies for spark ignition, that is, buy the best you can afford on the basis you want long engine life and enhanced fuel economy.  Since diesel engine oils by their nature have a greater degree of detergency and dispersancy than petrol engine oils, these also make suitable oils for older mechanically controlled petrol engines that produce more sludge and combustion products in the sump. 

Commercial Ratings – Diesel/Compression Ignition Engines

Category

Status

Service

CJ-4

Current

Introduced in 2006. For high-speed, four-stroke engines designed to meet 2007 model year 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 (0.0015% by weight) Sulphur fuel may impact exhaust after-treatment system durability where particulate filters and other advanced after-treatment systems are used. Optimum protection is provided for control of catalyst poisoning, particulate filter blocking, engine wear, piston deposits, low- and high-temperature stability, soot handling properties, oxidative thickening, foaming and viscosity loss due to shear. API CJ-4 oils exceed the performance criteria of API CI-4 with CI-4 PLUS, CI-4, CH-4, CG-4 and CF-4 and can effectively lubricate engines calling for those API Service Categories. When using CJ-4 oil with higher than 15ppm Sulphur fuel, consult the engine manufacturer for service interval.

CI-4

Current

Introduced in 2002. For high-speed, four-stroke engines designed to meet 2004 exhaust emission standards implemented in 2002. CI-4 oils are formulated to sustain engine durability where exhaust gas recirculation (EGR) is used and are intended for use with diesel fuels ranging in Sulphur content up to 0.5% weight. Can be used in place of CD, CE, CF-4, CG-4 and CH-4 oils. Some CI-4 oils may also qualify for the CI-4 PLUS designation.

CH-4

Current

Introduced in 1998. For high-speed, four-stroke engines designed to meet 1998 exhaust emission standards. CH-4 oils are specifically compounded for use with diesel fuels ranging in Sulphur content up to 0.5% weight.  Can be used in place of CD, CE, CF-4 and CG-4 oils.

CG-4

Current

Introduced in 1995. For severe duty, high-speed, four-stroke engines using fuel with less than 0.5% weight Sulphur. CG-4 oils are required for engines meeting 1994 emission standards. Can be used in place of CD and CE oils.

CF-4

Current

Introduced in 1990. For high-speed, four-stroke, naturally aspirated and turbocharged engines. Can be used in place of CD and CE oils.

CF-2

Current

Introduced in 1994. For severe duty, two-stroke-cycle engines. Can be used in place of CD-II oils.

CF

Current

Introduced in 1994. For off-road, indirect-injected and other diesel engines including those using fuel with over 0.5% weight Sulphur. Can be used in place of CD oils.

CE

Obsolete

Introduced in 1985. For high-speed, four-stroke, naturally aspirated and turbocharged engines.  Can be used in place of CD oils.

CD-II

Obsolete

Introduced in 1985. For two-stroke cycle engines.

CD

Obsolete

Introduced in 1955. For certain naturally aspirated and turbocharged engines.

CC

Obsolete

CAUTION: Not suitable for use in diesel-powered automotive engines built after 1990.

CB

Obsolete

CAUTION: Not suitable for use in diesel-powered automotive engines built after 1961.

CA

Obsolete

CAUTION: Not suitable for use in diesel-powered automotive engines built after 1959.

 Table 7 – API Commercial Oil Ratings

   

API ratings for Gear Oils

Gear oils are also classified by the American Petroleum Institute under the  GL rating system. 

See Viscosity Explained for an understanding of the SAE Gear Oil grading system.

Again, gear oils can be either mineral or synthetic and because they are not as challenged as an engine oil, they last longer.  IN fact some car manufacturers now do a fill-for-life with quality synthetic.  Multi-grade gear oils are also more common now, as there is some period of warm up and possible extra drag when cold.  Synthetic based multi-grade oils are less likely to sheardown than the mineral based multi-grades with VI Improver additives.

MGBs and a number of other British classics use a Laycock overdrive.  The oil specified for this is usually engine oil in 20W50 format and gear oil is not recommended.  However, earlier non-overdrive gearboxes were specified with EP90 oil.  Some owners complain of sluggish overdrive operation when the gearbox is cold so it is possible that the box has been incorrectly filled with EP90.  The EP90 is not so much a problem with the copper in the gearbox but more to do with the friction drive through the cone clutch and subsequent slipping.

API classification subdivides all transmission oils into 6 classes (sourced from Wikipedia):

    API GL-1, oils for light conditions. They consist of base oils generally without friction modifier additives. GL-1 may contain small amounts of anti-oxidant additives, corrosion inhibitors, depressants and anti-foam additives. API GL-1 oils are designed for spiral-bevel, worm gears and manual transmissions without synchromesh rings typically found in agricultural applications.

    API GL-2, oils for moderate conditions. GL-2 contain anti wear (AW) additives and are designed for worm gears. Recommended for proper lubrication of agricultural machine transmissions.

    API GL-3, oils for moderate conditions. GL-3 contain up to 2.7% anti-wear additives. Designed for lubricating bevel and other gears of truck transmissions. GL-3 are not recommended for hypoid gears.

    API GL-4, oils for various conditions - light to heavy. GL-4 contain up to 4.0% effective anti-scuffing additives. Designed for bevel and hypoid gears which have small displacement of their axes, truck gearboxes, and axle units. GL-4 are recommended for non-synchro gearboxes of US trucks, tractors and buses and for main and other gears of all vehicles. GL-4 oils are basic for synchronized gearboxes, especially in Europe.

    API GL-5, oils for severe conditions. They contain up to 6.5% effective anti-scuffing additives. The general application of GL-5 in this class are for hypoid gears having significant displacement of axes. GL-5 are recommended as universal oils to all other units of mechanical transmission (except gearboxes). GL-5 oils, which have special approval of vehicle manufacturers, can be used in synchro manual gearboxes only. API GL-5 oils can be used in limited slip differentials if they correspond to the requirements of specification MIL-L-2105D or ZF TE-ML-05. In this case the designation of class will be another, for example API GL-5+ or API GL-5 LS.

    API GL-6, oils for very heavy conditions (high speeds of sliding and significant shock loadings). They contain up to 10% high performance anti-scuffing additives. They are designed for hypoid gears with significant displacement of axes. Class API GL-6 is not applied any more as it is considered that class API GL-5 is enough to meet the most severe requirements.

    API MT-1, oils formulated for thermal stability, with 10% EP additives and friction modifiers.  Generally suited for non-synchromesh manual gearboxes in heavy duty service such as bus and truck fleets.

ATF or Automatic Transmission Fluid is purposely coloured with a red dye to aid condition checking.  If the oil darkens it indicates a need for change and possible problems in the unit.  Some owners use it in their MGBs and Midgets as the colour can aid identification of the source of the persistent oil leak and it won't cause harm to the overdrive, which is, in effect, a form of automatic transmission utilising hydraulic power to switch in and out.

However, ATF usually conforms to various OEM specifications such as Dexron and Mercon.  Check with the handbook for your vehicle as to which is required.

Owners of MGs fitted with the LT77/R380 box have seen a number of oils types specified by the factory.  During the 1990s Texaco provided a specification for most Rover gearboxes, MTF94.  A copy of the spec sheet is here.

Where can I find the API rating?

The API rating is usually shown in a doughnut or circle on the side of the oil container, or may be listed in the small print.  Not all manufacturers show this on their containers, possibly for the reason that not many people know what it means, or more cynically, because it hasn’t been fully tested. 

Oil companies are now also seeking manufacturer approvals so the text on an oil container may also include all the list of manufacturer approvals.  This is not necessarily quantifying a performance claim; merely that it meets the specification called for by that manufacturer.  However, often the implication is that if it is good enough for a German manufacturer then it will be good enough for anyone.

Ultimately the specific product data sheet will have the most useful information and will contain information on both the physical and chemical properties of the oil as well as certain performance test results undertaken in the laboratory.  Be aware that downloading these technical sheets from the internet can lead to confusion as products with the same name may differ from region to region owing to local market conditions and demand and base oil sources etc.

In independent testing that I have been involved with in the past, there have been significant differences in wear control between major brands.  Don’t write off smaller brands, either.  Some smaller brands specialise in a type of oil and do not carry the overheads of a major supplier.  They dedicate their facilities to a type of base stock, operate in a cleaner manner, and use higher quality base stocks with specifically formulated additive packages.  But better quality and performance will usually cost more.

For older engine designs, if you want to avoid the very latest API spec, use one that is designed for older engines.  Halfords, Castrol, Comma and Millers do a range of classic oils in the UK, and Penrite is also available from Australia.  Millers even do a specific 20W50 for the A Series with the gearbox in the sump.

The advice with classic petrol engines is to look for modern oils that have been formulated for diesel engine use as well.  If the oil has a CH-4 or CI-4 rating then this should be more than adequate for valve train protection, even if it is an SL rated oil.  An SM oil will still offer protection but in a different way to the way SL/CI-4 oils did using ZDDP.

Now, it is true to say that newer engines should not run on oils formulated for older engines, but they can, albeit with reduced engine life and performance.  There's a tendency in the classic car community to think older engines can't run on newer oils, not helped by the marketing of specialist oils for the classic community.  Older engines can run on newer oils.  If you look at the way API define each new category they state "For xxxx (year) and older engines", so consequently even up to SM oils should be acceptable for older engines.  That said, SM qualifying oils have been formulated for the very latest energy conservation which puts emission control above wear control.  But that said, oils that qualified for an earlier category may automatically qualify for the next new category simply because, as said, an oil must meet or exceed the minimum criteria.  

There has been a recent trend by some experts to suggest not using an API oil higher than SG.  The reasoning given is these lack sufficient Zinc protection.  As mentioned earlier, Zinc levels are still much higher than they ever were in the SA/SB/SC oils on which the A and B Series would have first run.  Certainly, in 1993, in the UK, exhaust catalytic converters became compulsory fitment for vehicle manufacturers, and Zinc is damaging for these.  Now API SG is for engines built in 1993 and older.  But API is a North American focussed organisation so I am not sure if there is any link between the change in test parametres for SG to SH categories and the UK requirement for catalytic converters which were being used on many cars long before 1993, anyway.  The API ratings do state for 199x engines and older and do not specifically exclude engines built before 1979.  By rights MGBs should be on SB/SC oils given the date of its original engine, however, experienced engine builders seem to differ in their views regarding synthetics and modern SL spec oils with some praising these oils and some hating these oils.

In fact, as SG is an obsolete category now you would struggle to find an SG oil today, without going to the specialist classic car oils, and these probably won't have been submitted for API SG testing.

This is what the British Lubricants Federation (BLF) has to say regarding advice given to owners of petrol engines:

"Any oil which does not carry an API or ACEA performance specification or some type of approval from a major vehicle manufacturer is highly suspect and must be assumed to fall into the lowest category, i.e. API SA, which became obsolete in the 1930s when the first additive engine oils (API SB) began to appear!  

It is essential that oils of at least the correct requirement are used, although higher specification oils, in the same category, should be used as soon as they become available if maximum benefits in fuel economy, engine protection performance and operating costs are to be obtained.  

However, it must be appreciated that an engine which has been operating on a very poor-quality lubricant for some time may well be beyond saving, since it is likely to have suffered build-up of sludge deposits which could be displaced by the detergency power of a modern good-quality oil. Blocked oilways could well result.

Currently there is no UK legislation to ensure that all oils marketed are fit for the purpose, although it is the case in some other countries.

Technology has moved on since the 1930s at an enormous rate, and such oils, which are no longer compatible with modern engines, should now be relegated to a museum, along with, for example, mechanical typewriters, ‘cats-whisker radios’, and other 1930s technology."

Likewise for diesel engine owners.

"Any oil which does not carry an API or ACEA performance specification or some type of approval from a major vehicle manufacturer is highly suspect and in the interest of safety must be assumed to fall into the lowest category, i.e. API CA, which became obsolete in the 1950s.  

It is essential that oils of at least the correct requirement are used, although higher specification oils, in the same category, should be used as soon as they become available if maximum benefits in fuel economy, engine protection performance and operating costs are to be obtained. However, it must be appreciated that an engine which has been operating on a very poor-quality lubricant for some time may well be beyond saving, since it is likely to have suffered build-up of sludge deposits which could be displaced by the detergency power of a modern good-quality oil. Blocked oilways could well result.

 Unlike in some other countries, there is currently no legislation in the UK to ensure that all oils marketed are fit for purpose. It is recommended therefore that as a minimum all end-users seek confirmation from their suppliers that the oil selected is fit for the intended purpose. Furthermore the BLF suggests that documentary evidence is provided."

 

Other Ratings – ACEA

Figure 6 - ACEA Ratings Explained

A/B : gasoline and diesel engine oils

    • 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.

C : Catalyst compatibility oils

    • 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 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.

    • SAPS : Sulphated Ash, Phosphorus, Sulphur           

    • DPF : Diesel Particulate Filter

    • TWC : Three way catalyst                 

    • HTHS : High temperature / High shear rate viscosity

 

E : Heavy Duty Diesel engine oils

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

ILSAC

The International Lubricant Standardization and Approval Committee (ILSAC) also has standards for motor oil. Their latest standard, GF-4 was approved in 2004. A key test is the Sequence IIIG, which involves running a 3.8 L, GM 3.8 L V-6 at 125 horsepower (93 kW), 3600 rpm, and 150 °C (300 °F) oil temperature for 100 hours. These are much more severe conditions than any API-specified oil was designed for: cars which typically push their oil temperature consistently above 100°C (212°F) are most turbo-charged engines, along with most engines of European or Japanese origin, particularly small capacity, high power output.

The IIIG test is about 50% more difficult than the previous IIIF test, used in GF-3 and API SL oils. Engine oils bearing the API starburst symbol since 2005 are ILSAC GF-4 compliant.

 

JASO

The Japanese Automotive Standards Organization (JASO) has come up with their own set of performance and quality standards for petrol engines of Japanese origin.

For 4-stroke gasoline engines, the JASO T904 standard is used, and is particularly relevant to motorcycle engines. The JASO T904-MA and MA2 standards are designed to distinguish oils that are approved for wet clutch use, and the JASO T904-MB standard is not suitable for wet clutch use.

For 2-stroke gasoline engines, the JASO M345 (FA, FB, FC) standard is used, and this refers particularly to low ash, lubricity, detergency, low smoke and exhaust blocking.

These standards, especially JASO-MA and JASO-FC, are designed to address oil-requirement issues not addressed by the API service categories.