Over the Counter Zinc Additive

Well, I wondered why you were using half a bottle and it now makes sense. And I found that slantsixdan made the same analysis of the Lucas additive many years ago on FABO.

I've been looking for any info that might indicate that adding excess ZDDP additive is necessary to reach the desired levels because of some strange reaction or 'loss' of ZDDP, but I have not found anything so far.

ZDDP can decompose but it takes temps up in the 150C range or higher. One thing that did come up is the if the ZDDP decomposes, one byproduct is hydrogen disulfide, which is the rotten egg smell. So if you ZDDP additive smells like rotten eggs, maybe it set in a hot truck trailer for a few days. I'd toss it.

Uh-oh... now we'll have all sorts of car guys hospitalized for 'ZDDP sniffing'... LOL