Erik VanRenselaar
Member
Is there an ideal additive product for those of us who use modern off-the-shelf motor oils in their pre-1981 engines? I see that the stp oil treatment touts that it contains zddp.

hi eric,
the swepco 502 oil improver contains both zinc and micronized moly. One pint treats up to 5 quarts of oil and at that rate will increase the zinc by approx 175ppm. It is not recommended for engines requiring sm, sn or cj-4 oils as it will increase the level and put it out of spec for those newer engines which are 2007 and newer.
Units of 502 are available from IH Parts America. For more information go to the "lubricants" section.
Incidently, the treatment ratio mentioned above will increase the zinc level to around 1,000 ppm, whereas the swepco 306 engine oil in 10w30, 15w40 and 20w50 has a +/- 1,600 ppm level of zinc and 1,200 ppm of phosphorous. Those are also available at IH Parts America under the same tag of "lubricants."
I use zddplus
it actually has zddp in it and that is what our engines really need.
Zddp (zinc dialkyldithiophosphate) is not the same as zinc or moly

icefyre13th,
it sounds like you know a lot about engine oil.
I cannot refute your statement about se engine oils containing more zddp than sl does as I am not privy to the formulas, even at that time. But saying that what you state is correct, the point is that the question was "what engine oil can I use in my Scout engines" (paraphrased).
I've done a little research in my api specifications and found that se was warranty approved in 1972, so your time frame is correct, however, it was replaced by sf in 1980 as warranty approved (regardless of the amount of zddp) and became obsolete in 1989.
You will have to agree that not only could the zddp been changed over the years, but most of the other additives and base stocks have as well, and mostly for the good.
You cannot get se any longer, in fact you would probably have to look real hard to get sl. So my recommendation still stands that swepco 306 sl engine oil would be the best I can make. There May be others and as this is a capitalistic society, you certainly have the right to find it, and use it as you see fit. IHPA is a valued customer of mine, and a firm believer in our products, and as long as that relationship exists there is no point in further pursuing this issue. I have no issues with zddplus as I have had permission from them to do some articles in the past.
steve,
... The zddp additive levels are higher than most so-called specialized racing oils ...
Dick