Chapter Seven – What is the terminology from SAE and API?
Many think that the “W” in 10W-30 means “winter”.
Two series of viscosity grades are defined in Table (1): (a) those containing the letter W and (b) those without. Single viscosity grade oils with the letter W are defined by maximum low temperature cranking and pumping viscosities and a minimum kinematic viscosity at 100°C.
Single grade oils without the letter W are based on a set of minimum and maximum kinematic viscosities at 100°C and a minimum high shear rate viscosity at 150°C.
The shear rate will depend on the test method. Multi-grade grade oils are defined by both of these criteria…
The W is just a designation of one type of testing vs another.
What is the viscosity of the various grade oils? The definitions are as follows:
|20||5.6 - 9.2|
|30||9.3 - 12.4|
|40||12.5 - 16.2|
|50||16.3 - 21.8|
|60||21.9 - 26.1|
|40||2.9 - 3.7|
Note again that the difference between the 20 grade and 60 grade oils at 302 F is only about 1 (one). Whereas the difference in viscosity at 104°F is 120 units. The 20 grade has a viscosity of 40 and the 60 grade a viscosity of 160. The difference at startup (75°F) is even higher, probably 250 or 300. At ice cold temperatures the difference is in the thousands.
The American Petroleum Institute, API, and Society of Automotive Engineers, SAE, have rated engine oil performance over the years. We have seen the ratings go from SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL with SM to follow. SI and SK were eliminated as they are used by other businesses. There are over 3 dozen tests that oil now must pass in order to make the next higher rating. The tests are defined by the American Society for Testing and Materials, ASTM. Some tests have progressed to a zero tolerance level. For example there can be no sticking of any piston rings any more. I will compare the SL rated oil to the previous SJ oil in a few categories. For simplicity I will skip the units of measurement:
|Maximum cam plus lifter wear||30||20|
|Varnish rating (higher is better)||5||8.9|
|High temperature deposits||60||45|
|High temperature volatility||70||10|
Other categories include: Resistance to rust, resistance to foaming, resistance to oil consumption, homogeneity and miscibility, flow reduction with varying amounts of absorbed moisture, gelation index and others.
As one can see just going from the previous SJ to the SL rating is a significant improvement. I cannot wait to get the upcoming SM oil into my cars. This is the current rating as of April 2010.
4. Because engine pumping, cranking and starting are all important at low temperatures the selection of an oil for winter operation should consider both the viscosity required for oil flow as well as cranking and starting, at the lowest expected ambient temperature.
Pumping viscosity is a measure of an oils ability to flow…during the initial stages of operation.
Test in ASTM D 4684. ….samples are tested after a slow cool cycle. This cycle has predicted as failures several SAE 10W-30 and 10W-40 oils which are known to have suffered pumping failures in the field after short-term (2 days or less) cooling. These field failures are believed to be the result of the oil forming gel structures that result in excessive yield stress and viscosity of the engine oil…
A.2.1…After preliminary warming, the sample is subjected to a controlled temperature/time cycle over 5 1/2 to 7 days. The cycle reproduces …instability or reversion which has occurred during storage of oils in moderately cold cyclic conditions. Recent work shows relevance to engine oil pumpability failure. Oils exhibiting pour reversion have solids resulting from wax gel formation, at temperatures significantly higher than their ASTM D 97 pour points.
Extracted, from ASTM D 4485-03 Standard Specification for Performance of Engine Oils, copyright ASTM International,
100 Barr Harbor Drive, Wets Conshohocken, PA 19428, USA.
My point is that tests are not just laboratory concoctions. They design tests to match real life conditions.
I used 5W-20 Pennzoil mineral based multi-grade oil in my Expedition as it has many of the low temperature characteristics of higher grade synthetic oils. My ’04 manual states that the SUV is delivered with a Ford semi-synthetic oil and although regular oil can be used they recommend a semi or full synthetic oil. For the differential gear oil they used 75W-140 in my ‘98 Expedition but now recommend 75W-90. If I was towing 8,000 lbs. then I would need the semi or full synthetic 5W-20. But for my usual around town driving a plain, mineral based oil is plenty good.
Please note that it makes no difference what oil you are using. The 0W-20 Mobil 1 that is SL rated meets the same criteria as that SL rated 10W-30 synthetic or mineral based Pennzoil. That SJ or in particular that SH oil some people are looking for (from their older automotive owners manual) is no where near as good as any SL oil of today. Always use the most currently available, highest rated motor oil, even in the oldest, most worn engine. You may require a thicker grade but just make sure it is SL or SM rated.
The SH rating was used in oils starting 1993. The SJ rating started in 1997 while the SL became effective in 2001 oils. According to ASTM D 4485, SL rated oils are superior to previous oils and from:
X2.3.1 and 2: SL oil is for use in current and all earlier passenger cars, sport utility vehicles, vans, and light trucks. This SL rated oil can be used in engines requiring SJ and All Earlier Categories.
Concern: People are worried about the SM oils not having as much ZDDP as the SL and older oils. The reason ZDDP has been used for years is not because of its superior performance but rather its low cost and dual function as an antioxidant. It also has anticorrosive properties.
There are other additives. Some newer oils do not have any ZDDP, and they are excellent products. Just the same, I prefer oils with ZDP for now. The research shows that 0.03 is all that is needed and has the same function as higher levels. The only reason to have more is because your engine is consuming the ZDDP secondary to borderline lubrication from oil alone.
And lastly, too much can be corrosive itself and has shown in some tests to actually increase wear.
See these sites for more info.:
- American Society for Testing and Materials – www.astm.org
- Society of Automotive Engineers – www.sae.or
- American Petroleum Institute – www.api.org