Ama, once you understand oil rating numbers and letters, there's no such thing as obsolete, only "newer & better"
Oils are rated for Spark (gasoline) or Compression
A grade like "SF" or "SL" indicates it is for gasoline engines. As the specs, and oils, get better, the second letter changes. "SM" is now current
, SH is still common--and pretty good. You can go tot he source at Welcome To The API Website
for the API rating explanantions.
Engine Oil Guide: http://www.api.org/certifications/en...lGuide2006.pdf
A grade like CC, CD, CE, CF would indicate a diesel oil, again the higher second letter being the improved spec. Apparently Castrol no longer uses a separate diesel grading system but tags their new oil "SH" diesel oil. Not altogether surprising because the difference between diesel/gasoline oils has to do with the amount of ash and some specific other properties, and in theory you can make one oil with additives that meet both services--and have one less thing to distribute and inventory.
The numeric part of the oil specification, i.e. 15W40 or 10W30, actually is obsolete. A "straight 30" oil just marked "SAE 30" means that it falls through a special funnel at a specific rate, at a specific temperature, like honey pouring down a kitchen funnel. That's all that means--how thick the oil is, not how well it performs in any other way. When there are two SAE numbers, like 15W40, it means "this performs like a 15 in the W
inter, and a 40 in the summer". And the main significance there, is that the lower the "W"inter number is, the thinner the oil is in the cold, and the easier it is for your engine to start up when it is cold.
Today, they can build an oil that lubricates well pretty much regardless of termperature, so the SAE ratings really just tell you what temperature range the oil is good for (i.e. arctic or tropical use) and the API ratings (like SH) tell you that you've got a better oil than the older spec.
Any oil that has the same or similar API ratings, and an equal of better SAE rating, will work for you. Personally, I'd go with a fully synthetic oil (that's a long debate<G>) rated 0W40 or 5W40, because it starts up real easy, very little load on the starter, easier to start on low batteries, and I know that synthetic oils are engineered so they still have great protection--even though they are thinner in the cold temperature.
Some of it is a judgement call, i.e. a synthetic 30 might protect your engine in hot weather
just as well as an older 40. Or, if you have an older engine that burns a little oil, you might choose a 50 rating, which is thicker and leaks
past the rings less in high temperatures. (And robs just a little engine power, because it is thicker.)
Any oil on the market today, from any major vendor, is better than anything on the market 30 years ago. So don't loose too much sleep over it.<G>