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Yes, its ZDDP yet again. I bored and confused fellow TRers when I opened this can of worms, which I've copied over from the TR forum Many oil suppliers have changed the way they describe the concentration of ZDDP, and it makes a huge difference. An oil labelled as "1100 ppm ZDDP" contains much less ZDDP than one labelled as " 1100ppm Zn as ZDDP" Unitl recently all oils were labelled as " ppm Zn as ZDDP". the change has crept in under the radar. Zinc contributes only about 10-15% of the weight of the ZDDP molecule. So a crafty seller who wants to put a bigger ppm number on the label could easily use the mass of the whole ZDDP molecule. There are many different ZDDP molecular species varying in molecular mass from 400 to 2000.In any ZDDP molecule there are 1 Zinc and 2 Phosphorus with respective atomic weights of Zn=65 and P= 30. So if the whole ZDDP molecule weighs around 400, the Zn ( or P) contributes around 60-ish, or about 15%. SO an oil with say 200ppm Zn ( rubbish for our engines) could be labelled as having 1400 ppm ZDPP. That "1400 ppm ZDDP" would be scientifically correct and legal labelling (as far as I know) But it is not the way the level has been expressed in the past which was as ppm Zn. You'd buy the 1400, yes? but not 200 ppm. Beware !! WHAT to DO ? If the label says ZDDP as Zn ( or P) = 1100 to 1400 ppm region we are sure to be OK, and this is conventional labelling. If the label simply says ZDDP = 1100 to 1400 ppm ( or more!) we have no idea what the Zn or P content is, and the oil may be at least 7 times lower in ZDDP than we expect. That is b88ger all antiscuff. I would not buy that oil without supplier's lab (not a sales person) confirming the Zn or P ppm. Apologies for the long-winded explanation - sometimes science does not reduce to commonsense explanations. ===================== Has anyone seen this in a classic car mag or elsewhere? Peter