What’s the real ZDDP recommendation?

February 1, 2016 | By Staff


In your October MOD item regarding break-in oil you recommended 12,000- 14,000 ppm of ZDDP for antique cars. Then in the November issue, again regarding break-in oil, you recommended 1200. I feel it probably is 12,000 but not being a super mechanic like most of you guys I check everything. Fortunately, I have a neighbor that’s a great mechanic. I have four antique cars (’55 Ford, ’64 Chevy, ’72 VW and ’79 MGB) that I’m going to convert to synthetic oil. Do I need to add any ZDDP to this oil? I give away lots of magazines after I read them but never an Auto Restorer. I read and re-read every issue. Keep them coming.


The typo is with the higher figures. We added one too many zeros. Fact is, 1200 is the minimum needed for flat tappet engines, but 1400- 1500 is better. The problem of scuffing gets much more serious if you put a high-performance cam and stiffer valve springs in your classic’s engine. In that case the cam will wear rapidly without the added ZDDP. And yes, there is a study by one oil company that says you don’t need ZDDP at all if you use their oil, but I have had personal experience with cam wear on freshly rebuilt classic engines, and have found that ZDDP solves the problem.

However, keep in mind that you would never want to use oil with ZDDP intended for classics with flat tappets in vehicles with catalytic converters and oxygen sensors, because it will damage them. That is why this additive was removed from modern motor oil. Modern oil works great in modern cars because they have roller tappets in them.

As for synthetic oil, we covered that in previous issues, but the best way to determine the appropriateness of any synthetic motor oil would be to contact the manufacturer to determine if their oil is suitable for your engine. Synthetic oil’s main virtue is that it can handle extreme temperatures.