Interpreting API motor oil service categories

[Duke W.]

In order to sort out the remaining confusion on current API service category labels I downloaded API document 1509 Engine Oil Licensing and Certification (EOLCS).

http://www.api.org/certifications/engineoil/pubs/upload/1509_16thedition042007.pdf

Feel free to read it yourself and draw your own conclusions, but for those who don't have a background in this area I have distilled out the salient facts/issues and offer the following guidelines for purchasing motor oils for both vintage and modern cars. As I have stated many times before, the ONLY criteria you need to use (for vintage car oil selection) are SAE viscosity range and service category. Virtually everything else offered up by oil marketers, including the word "synthetic" is marketing hype. This word does not appear ANYWHERE in the 125 page API 1509 document!

GENERAL DISCUSSION

The primary service category is the FIRST listed. Oils whose first listed service category is C... are intended primary for diesel engines, but are also suitable for spark ignition engines that require S-categories that follow the C-categories. For example, a common service category is CI-4/SL.

Motor oils whose FIRST listed service category is SM CANNOT carry any other API service category. SM oils that have winter viscosity grades of 0W, 5W, and 10W are limited to .08% (800 ppm) phosphorous by mass content, which limits the amount of ZDDP anti-wear additive. SM oils with winter viscosity grades above 10W are NOT limited in phosphorous content, however, that does not guarantee that the phosphorous content is greater than .08%.

Since SM oils with winter grade ratings above 10W have no phosphorous limitation, a CJ-4 oil that is above 10W can be labeled SM. Thus you will now commonly find 15W-40 rated CJ-4/SM.

FIRST CHOICE FOR VINTAGE CARS: 15W-40 CI-4/SL

Assuming you do not commonly start your vintage car below 15 degrees F. this is a suitable viscosity range for all cold start and driving conditions. These oils may also include a supplemental rating of CI-4 Plus, which will be found in the bottom of the API "donut". This means the oil has additional soot handling features, which is not an issue in spark ignition engines, so you can be indifferent to the CI-4 Plus supplemental rating for use in vintage car spark ignition engines.

SECOND CHOICE FOR VINTAGE CARS 15W-40 CJ-4/SM

This latest HD diesel engine oil designed for new catalyst equipped diesel engines has a different, slightly less rich additive package than CI-4, but the additive package is richer than any oil labeled SM. Given the light duty operation of typical vintage car use this oil is perfectly acceptable and will be easier to find at auto parts retail outlets than CI-4.

MODERN CARS

The first rule is to follow the manufacturer's requirements for warranty coverage. Most new cars will require SM, however, some, like Corvette, have a specific manufacturer's specficiation. If you have a truck or SUV and tow, consider using CJ-4/SM, however, you may only find these in winter grades above 10W, so it may not be suitable for winter use depending on your climate. CJ-4/SM can also be considered optional in new cars that see severe use such as race track hot lapping. In both cases CJ-4/SM rated oils may have winter viscosity grades above the lowest the manfacturer recommends, however, in hot weather/severe service this is not going to cause problems, but may be a technical violation of the manufacturer's warranty requirements.

Duke

[Richard F.]

Re: Interpreting API motor oil service categories

Alright, Sir, I've read the API stuff. I now understand why the SM is not as harmful if it comes on the label after the CJ. But unless I'm missing something, only the MAX of ZDDP was specified before SM. SM is the only S-class that specifies min AND max. I wonder how much we really used to be getting. But I'm not going to worry about it anymore. You've already convinced me the best course of action. Many thanks.

[Duke W.]

Re: Interpreting API motor oil service categories

The maximum phosphorous for SM is 0.08% with a minimum of 0.06% plus passing the wear test. SL requires a MINIMUM of 0.08% or more (with no specified maximum) if required to pass the wear test. The maximum for SJ is 0.10% and 0.12% for SH, and they probably required close to these levels to pass the wear test. One caveate is that these P maximums do not apply to any winter grade above 10W, so theoretically 20W-50 SM has no P limit, but I am not taking any chances. If you use SM in a vintage car, use one with a winter grade above 10W; 10W-30 definitely doesn't cut the mustard, and the only way to know if a 20W-50 SM has enough P is to have it analyzed.

I started getting nervous when I became aware to the changes to SL and saw what was coming with SM. I've been using CI-4 in my non-catalyst cars and CJ-4 in those with catalysts. If CI-4 ever actually disappears I will just use CJ-4 or follow-on C-category oils that are available in everything.

Duke

[Duke W.]

A final word on "synthetic"

API categorizes base oils in five groups - I, II, III, IV, and V. A primary classification criterion is viscosity index (VI). As we go up the group ladder, VI increases, which means the base oil has less viscosity change with temperature. An additional benefit as we go up the ladder is higher oxidation resistance. The particular manufacturing technologies to achieve the various base characteristics are NOT specified, but current manufacturing technologies correlate to the five groups as follows:

Group I - the lowest viscosity index, manufactured by conventional distillation and solvent extraction of crude oil.

Group II - "hydroprocessed" crude oil distillate stock, which breaks up chain molecules like aromatics that can lower the pour point, so the viscosity range is increased. Hydroprocessing also removes undesireable atoms like sulpher, and replaces them with hydrogen and increases the final product's oxidation resistance compared to Group I.

Group III - greater VI/oxidation resistance than Group II due to additional hydroprocessing or a better grade of crude oil that has fewer impurities.

Group IV - a special petrochemical process that creates polyalphaolefins (PAOs) that have a greater VI and oxidation resistance than Group III.

Group V - a special petrochemical process that creates esters than have greater VI and oxidation resistance than PAOs.

The original Mobil 1 synthetic oil from the seventies was either Group IV or Group V, and Mobil claimed you could run 25K miles between oil changes, but no OEM ever bought into this. Group IV and V base oils were developed for aircraft turbine engines that have continuous turbine inlet temperatures of 1500F or more and no cooling system per se, so their oil experiences exceptionally high temperature inside the engine and requires extremely high oxidation resistance and viscosity stability.

In the mid nineties Castrol introduced a "synthetic" oil that used Group II and III base oils. Mobil sued, and Mobil lost. The court determined than Castrol could continue to use Group II and III base oils and call their product "synthetic". The court essentially found that "synthetic" is a marketing, not a technical term.

In order to remain cost competitive, Mobil abandoned Group IV/V base oils and switched to a Group II/III blend like Castrol, however, retail prices did not really go down, so the resulting products had greater profit margin for both the corporations and retailers. Clearly, it was not in the "best interest" of the industry to shout the news through the fields and valleys, so few in the public including "car guys" knew of the above events or changes. Even the automotive press basically missed these significant events.

Few straight Group I base oils (with suitable additives) can pass current API test suites. Most need some added Group II or III base, but are still considered "conventional" or "mineral oil" base.

Any hydroprocessed oil, including Group II, can be called "synthetic" (but may not necessarily be labeled as such) and most current "synthetics" are primarily Group II base oil, but may have some Group III to enhance their properties. This characterizes current popular brand "synthetic" oils.

So be very careful about the use and meaning of "synthetic" when it comes to motor oil. Select an SAE viscosity range based on the expected temperature range that the vehicle will see, especially cold starts, type of engine technology (primarily valve gear), type of vehicle service - light or severe - and oil change mileage/time interval.

Vintage cars that don't frequently see cold starts below 15F don't need a 10W winter viscosity rating - a 15W is fine - and current C-category oils have a better additive package for flat tappet camshafts than S-category oils.

And for vintage cars that see low annual mileage accumulation, the oxidation resistance of a blend of Group I and II base oils is quite adequate, but change it at least annually.

Duke

[Scott S.]

Re: A final word on "synthetic"

For those of you who might like to expand your fluids knowledge & understand what Duke's talking about, try this link out & have fun.....

http://www.lubricantsuniversity.com

[Duke W.]

Re: A final word on "synthetic"

This is a truly excellent resource from a highly reputable source.

For those you you who don't have an educational/professional background in lubrication, go through the Fundamentals of Lubrication module.

After reading the CJ-4 module I no longer have any concerns about it being "less capable" than CI-4 in a vintage gasoline engine - or even an older diesel engine. Once my supply of CI-4 is consumed, I won't bother to look around for some obscure source. I will just use CJ-4 in everything!

Duke