: GM's response to ZDDP reduction in oil

02-22-11, 06:33 PM
Was reading through some old TechLink newsletters, found this one about Oil Myths. Now I don't want to start a flame war about what oil is best, and I'll say I'm one who uses oil with higher ZDDP and/or Engine Oil Supplement in my old sbc with a flat tappet cam.

But... GM said in 2007 that the new SM oil were tested with flat tappet cams and met their wear criteria. Further, they also say that the levels of Zinc and Phosphorus in the new oils are actually the same as oils from the '50s. ZDDP apparently was increased in the '60s to solve viscosity problems. That surprised me.


Those who hold onto the myth are ignoring the fact that the new Starburst oils contain about the same percentage of ZDP as the oils that solved the camshaft scuffing and wear issues back in the 1950s. (True, they do contain less ZDP than the oils that solved the oil thickening issues in the 1960s, but that's because they now contain high levels of ashless antioxidants not commercially available in the 1960s.)

Interesting, to say the least. Though I'm not sure I will run out and change my old engine oil to SM 10w30. I've seen plenty of cam lobes run flat... not to mention plenty of pictures on this forum of pre-2000 N* cams worn out. But at the same time I do know plenty of people who run SM oil in old engines and don't have a clue about ZDDP or have any issues.

02-22-11, 07:46 PM
Good link. That's interesting.