Modern Oil Use
We can't find the recommended oils for older vehicles any longer. Just as well, because even the worst modern oils have much better viscosity indexes and additive packages than the best oils of the years the old cars were made. Using LUBRIPLATE Non-Detergent Motor Oils as an example of a non-detergent API SA engine oil, we can see that the SAE 30 grade has a VI of 109 which would be a superior oil on the early VI scale.
However, a major issue for cars since the 1930s has been sludge and modern oils combat this problem with a variety of additives including detergents and dispersants. Detergents keep oil-insoluble contaminants in suspension and dispersants keep contaminants from agglomerating (i.e., remaining in a dispersed state).
Another issue, especially with modified engines having aftermarket high performance valve trains, is the protection of flat tappets. The sliding friction occurring as the valve lifter moves over the cam lobes can have excessive wear with high rate springs. The anti-wear additive commonly used for this protection is ZDDP (Zinc dialkyldithiophosphate), which has been reduced in the latest SN engine oils because its post-combustion ashes can poison catalytic converters and O2 sensors. The phosphorus component of ZDDP is what actually performs the anti-wear function.
Since many of the cars owned by ACCCC members generally do not have concerns with catalytic converters and since we would prefer all the anti-wear protection available in a modern engine oil, the best oils for flat tappet engines are the HDEOs used in diesel engines. CI-4 and CI-4+ HDEOs have the highest levels of ZDDP and and, because of nature of diesel combustion, also have the among best engine cleanliness additives. However, these engine oils are commonly found with 15W-40 viscosity, which is unnecessarily heavy for use in automotive engines. Higher than necessary viscosity results in increased engine friction which results in poorer fuel economy and wasted power.
HDEOs are also available with lower winter (W) ratings but are these are generally synthetic based. Commonly available HDEO viscosities include 5W-40 and 0W-40 in addition to 15W-40. 0W-30 HDEOs are also available from a few manufacturers. Although synthetic oils are generally about twice cost of conventional motor oils, it is possible to extend the oil change intervals (OCIs) significantly. Besides extended OCIs, synthetics have extremely low pour points and, therefore, flow readily at extremely low temperatures.
See the following Mobil videos for more information about the capabilities of synthetic engine oils: