I own a few older vehicles and recently got to wondering what the proper oil for my new (old) Chevy 230 hp V8 would be. Most marine engines built before the mid-90's had flat tappet cams, not the roller cams you see in modern engines. To prevent premature cam wear, oils for older engines need to be formulated with ZDDP, a Zinc and Phosphorus additive. Modern oils have reduced amounts of ZDDP because of EPA requirements and potential damage to catalytic converters.
I have long used Shell Rotella T3 15W40 in my elderly vehicles but recently learned it has been discontinued and replaced with Rotella T4. Talking to Shell lubrication engineers I've found that the new oil also offers the protection that my older engine needs. Another approach you can use is to use a ZDDP additive (about $10 per treatment) with your modern oil.
For oil geeks this table shows the specs of some of Shell's current and former oils.
