It's supposed to be backward compatible, but I wonder about really older cars, like 70s and back. That's one reason SpecialtyFormulations has SX-UP, to put back the additive levels of a 60's/70's era oil.
The only concern that I am aware of is the lowered amount of ZDDP and flat-tappet cams. If you are able to use a 15W-40 or straight 30, this is a non-issue, just use Delo 400, Rotella T or Delvac 1300 HDMO. ConocoPhillips also makes SG/CD? SAE 30 and 40 in Phillips and "76" brands for pre-1989 cars.
From Penrite site
An engine oil that contains about 0.1% phosphorus or higher, will easily provide the required anti wear properties for older engines.
The step from API SH to API SL was accomplished by a combination of new additives or adding additional anti wear and anti oxidant to existing blends. These were not phosphorus based, but used organic molybdenum additives, to keep phosphorus levels at 0.1%.
Now we have API SM – for the first time, the limit on phosphorus is from 0.06-0.08%. There are industry concerns about the applicability of these oils in older engines. However, the limit only applies to 0W-20, 0W-30, 5W-20, 5W-30 and 10W-30 oils (so called “ILSAC” grades). Any other grades are exempt from this.
Therefore even blanket statements about API SM oils will be incorrect and further research will be needed by the end user.
There is one other factor with non-ILSAC oil grades. If they also have the European ACEA A2/A3 with B2/B3 or B4 performance levels, phosphorus levels will also be at 0.10 % to 0.12% as their tests have been more severe than the API for some time. Hence an oil that is SL (SM)/CF/A3/B3 also well exceeds the anti-wear requirements for older engines.
The irony is that API SF and SG oils formulated in recent years usually have phosphorus contents of around 0.08% (usually 0.1% maximum) anyway due to other advances in technology, unless the blender chooses to add extra additive.
Somebody else recommended the use of VSOT for my '69 ford small block if using SM rated oils. The idea was that the flat tappet lifters needed the extra zddp offered by VSOT. Having heard this a few times, I think Jimbo might have a point here.
From what I have read here, API ratings are alphabetically progrssive. Therefore, an API rating of SH is better than SG, and SL is better than SG, etc... Is this correct?
Secondly, do oils with a higher rating (SL, SM) work as well in an older vechicle that initially recommended a "lower rated" (SG, SH) oil? My interpretation of vehicle requirements would be that a vehicle requiring an SG rating should have an oil that meets or exceeds that rating. Is this a viable interpretation?
I agree with the extra zddp. i'm not convinced that the reduced level is good, but since 99% of the motor oil I sell is 15W-40 or 20W-50, we use a full CI-4/SL package in a Group II base oil and have excellent results.
- BTW... probably less than 0.1% of the cars here have catalytic converters.