What engine oil should be used since zinc compound is on longer in the present oil?

The absence of high levels of zinc (ZDDP) in modern engine oils isn't something to be overly concerned about, as it's a result of environmental regulations and advancements in engine technology. Older engines, particularly flat tappet cam engines, benefited greatly from the higher ZDDP levels for anti-wear protection. Modern engines, however, use different materials and designs that require less ZDDP.

So, what oil should you use? It depends entirely on your engine:

* Modern engines (post-2000s, generally): These engines are designed to run on modern, low-ZDDP oils. Use an oil that meets the manufacturer's specifications, as listed in your owner's manual. This specification will usually be something like a SAE rating (e.g., 5W-30, 10W-40) and an API certification (e.g., SN Plus, SP). Follow the manufacturer's recommendations religiously.

* Older engines (pre-2000s, especially flat tappet cam engines): These engines may benefit from oils formulated with higher ZDDP levels. You'll likely need to look for oils explicitly labeled as suitable for "classic cars," "flat tappet cam engines," or those specifying higher levels of ZDDP. Consult with experienced mechanics specializing in classic cars for recommendations. Adding ZDDP additives to modern oils is generally discouraged as it may cause problems in newer engines.

In short: Don't focus on the absence of ZDDP as a primary factor in oil selection. Instead, prioritize using the oil specifically recommended by your vehicle manufacturer. Using the incorrect oil can lead to engine damage regardless of ZDDP content. If you have an older engine with unique needs, consult a specialist.