I never heard of ZDDP until a few years ago when all of a sudden there were rumors of a number of unexplained camshaft failures in British cars. The rash of such failures coincided with the removal of ZDDP from engine oils thinner than 50 weight. I learned this in a conversation with a petroleum engineer at Brad Penn. A new API standard of SM accompanied the change. The evidence for the lack of ZDDP being the cause of the failures is entirely anecdotal as no scientific testing was done. But it also rests on the known properties of ZDDP as the high-pressure additive. Such testing would be very expensive, so no oil company is going to sponsor it, nor are the engine makers who have designed around the issue.
I have never heard of a cam failure in a 356 engine which can be definitively attributed to the lack of ZDDP.
This type of situation is not unusual. In my career in high tech engineering, I confronted many situations where reducing the failure rate through straight forward testing would have been far too expensive.
So, I choose to put the ZDDP back in through use of 15 or 20W-50 oil.
OIL CHANGE AFTER BREAKIN
- Harlan Halsey
- 356 Fan
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