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Bob,
Asking “What is the best oil” is a good way to open a can of worms. Generally, most oil today is better than anything available back in the day. The chart below (and the Owners Manual) recommends SAE 30 for normal warm weather driving and 20 for winter and 40 for hot weather. A good Multi grade such as 10-30 will also be OK. Some people use certain Delo or Shell Rotella 15-40. These are Diesel oils, but also are rated for gasoline engines and are available in bulk (cheaper).
One of the controversial issues with oil is whether to use Detergent or Non detergent. If the prior owner has been using detergent oil, or the engine doesn’t have a lot of miles, I would recommend continuing to use it. If the engine has a lot of miles and has built up sludge, many people suggest a non detergent oil as there is some concern that detergent oil may loosen deposits and block oil passages. I have not seen this, but others say they have. You will have to make your own choice. Pulling the oil pan on a new to you car is a good idea as you can check the internal condition of the engine and determine if there is any sludge. Detergent oil suspends particulate in the oil for the oil filter to remove. Non detergent oil lets the particulate drop out and settle in the engine forming sludge. Your engine has a partial flow filter (the canister at the left front of the engine).
The other controversy with oil is the amount of ZDDP (Zinc / Phosphorus ). Newer oils have less ZDDP because it damages catalytic converters, but they still contain some. ZDDP was not added to oil until the 1940s, so when your car was new no oil had it. There is some evidence that lack of ZDDP may cause cam/lifter damage, but this is in high compression or newly overhauled engines. Modern oils have a number of anti wear additives that older oils do not.
I would suggest if you have concerns about either of these topics, you do some internet research on them. Just make sure the opinion you are reading is backed up with actual evidence, not that “My friend’s uncle says that….. ”
Not owning an 8 cylinder car, I don’t know what modern filter will work. Hopefully someone else can chime in.
You can search all of the Service Bulletins using the Technical Search tool under the Publications tab in the Members pages. It takes a little practice to get the search terms right, but usually you can get results to questions.
Service Bulletin 1995-6 (available under Publications) has an article on oil filters for early 8s. A clearer copy of the chart below is in Service Bulletin 1981-2.
Dave
I am not going to suggest oil, you have received excellent information and advice already, but I will give a huge shout out about the modern replaceable oil filter holder that I bought from John Cislak. Its appearance is exactly like an original but it holds a modern screw-on filter inside that only costs a few bucks at NAPA. Considering the age and, more importantly, the internal conditions of any original filters that might be available this is a great alternative!
