Few questions after reading the whole thread....
Even though ZDDP has been taken out of oil due to Gov't mandates, is there something being put in place of it to help protect engines? For example, I remember reading somewhere that Valvoline Synpower has a formula that does not have as much ZDDP as SL rated oils, but in turn has something else that makes it good for flat tappet cams. I can't recall everything I read in the article as it was some time ago. If you think about it, wouldn't the companies have to put something in the oils that make it lubricate better (since oils are improving) otherwise they would have many lawsuits over destroyed engines. I know most modern engines don't use flat tappets, but think about how many millions of 4.0L's are on the road...
For example, the chemical properties of synthetic make it have better lubricating properties than conventional oil, would these better oil formulations have enough lubricating properties that ZDDP wouldn't be needed? Yes ZDDP has been known as a good lubricant in the past for flat tappets, but is there something in current oils that does the same thing?
Has there been any known cam failures do to using SM rated oils, seeing how the average person probably isn't aware of the issue, and most oils on store shelves are SM rated oils?
Is there any known ZDDP additives that you can buy and add to SM rated oils?
Not trying to question everyones beliefs by any means, I just don't hear of many 4.0 cam failures considering how many forums I am a part of and how many jeeps I am around. You would think oils would be made to lubricate more, not less. I've been wrong before though. :roll:
Edit: there also seems to be a big controversy over this issue. Some make it sound like if you buy SM rated oil that the jeep will blow at 100k miles while others (namely Bob is the oil guy Forum) make it sound like the 4.0L doesn't really seem to care what oil it has in it.