For the very interested, there is a fabulous web resource at www.bobistheoilguy.com about all things oily. Zddp is not the whole story, but there is general consensus that its quite valuable in a flat tappet camed engine, PARTICULARLY during break-in. SL and SM oils do have some of it, but less as has been noted. Moreover, even the new diesel engines are getting catalytics, SO you cannot assume that a diesel rated oil has more zddp either. Keep in mind that additives are consumed/broken down over the life of the oil, which in many vehicles is now assumed to be 3-5k miles. Fresh SM oil in an old engine should be just fine for 2k miles, which is more then most of us put on old babied engines before we change oil as well. Another point: High mileage and heavy duty engines oils, especially those rated at 15w40 and 10w40 are not covered by the same formulation rules -- they typically have more zddp, and sometimes some other goodies to swell old leaky seals. I would warrant that most of our older engines should be running 15w40 in the Spring/Summer/Fall anyhow and have 10w30 only in them for the occasional winter start. Finally, there is a lot of consensus that synthetic oils are more trouble and unpredictable in older engines. There are issues of the cam lobes -- some say synthetics "stick" to the metal better, some say the opposite. Generally accepted is that synthetics can produce more leaks, a clear problem in older engines. Synths help achieve longer oil change intervals -- they don't protect an engine from wear any better at all for the first 3k miles and probably aren't any better even up to 5k. Europeans like them a lot since they spec much longer OCIs than we get here in USA. There -- my first post here. Hope its been helpful.... David Hermanns -----Original Message----- From: mailing-list-owner@xxxxxxxxxxxxxxxx [mailto:mailing-list-owner@xxxxxxxxxxxxxxxx] On Behalf Of Dick Benjamin Sent: Tuesday, September 05, 2006 11:43 PM To: mailing-list@xxxxxxxxxxxxxxxx Subject: IML: How about Synthetic oils? (Ken Lang's question) I'll try to answer this - if it goes through, maybe things are working again. Yes, unless the synthetic oil is recommended for use in Diesels, I doubt very much that it contains enough ZDDP for use in car which is seldom driven. The reason for that is that in order to qualify for an SL or SM rating (look on your oil container), the Zinc Anti-wear additive has been eliminate to avoid poisoning the catalytic converter in modern cars. In other words, if it is sold for use in modern cars, it isn't the right stuff for a collector car that is parked for weeks at a time. When Mobil One first came out, this wasn't so serious a problem, but the SL and SM rated oils have really dropped the amount of ZDDP to just about zero - the SK article gives precise numbers, which I don't have at the tips of my fingers at the moment. Dick Benjamin -----Original Message----- From: mailing-list-owner@xxxxxxxxxxxxxxxx [mailto:mailing-list-owner@xxxxxxxxxxxxxxxx] On Behalf Of Ken Lang Sent: Tuesday, September 05, 2006 3:44 PM To: mailing-list@xxxxxxxxxxxxxxxx Subject: RE: IML: New Info on engine Oils - was lifter info - From Dick B. I'm wondering if this applies to synthetic oils as well. I've been using Mobil One in my 67. ----------------- http://www.imperialclub.com ----------------- This message was sent to you by the Imperial Mailing List. Please reply to mailing-list@xxxxxxxxxxxxxxxx and your response will be shared with everyone. Private messages (and attachments) for the Administrators should be sent to webmaster@xxxxxxxxxxxxxxxx To UN-SUBSCRIBE, go to http://imperialclub.com/unsubscribe.htm ----------------- http://www.imperialclub.com ----------------- This message was sent to you by the Imperial Mailing List. Please reply to mailing-list@xxxxxxxxxxxxxxxx and your response will be shared with everyone. Private messages (and attachments) for the Administrators should be sent to webmaster@xxxxxxxxxxxxxxxx To UN-SUBSCRIBE, go to http://imperialclub.com/unsubscribe.htm