Re: High Zinc (ZDDP) Engine Oil: My 2 cents
Here's my take on this:
Because the T-head is not really a "flat tappet" engine (lifters are radiused) and the valve spring pressures are really low compared to an automotive engine I think any good diesel rated oil should be fine for these engines. I use 10w-30 Rotella w/ WIX filters. Have seen no issues with the lifters (no changes in valve clearance over time) and the additive package in the diesel oil keeps the engine very clean and sludge free. All of mine are full flow oil systems; don't know what effect this oil would have on the older bypass filter system.
High zinc racing and break-in oils are very expensive compared to Rotella (at least double or more); if you are worried about the oil just change it twice as often and you still will be ahead. Oil really is cheap compared to fixing worn out parts. I believe that most of the suspected oil related wear in the L engines is the result of dirt contamination, transmission related wear contaminants and water damage, not the lack of zinc in the new oils.