I generally like
Engine Builder articles. There's also more info out there by equally knowledge writers who also reference their sources. So those are worth reading too.
Most important IMO is to find out the details of the specific oil being selected. Due to a variety of reasons the additive packages are not the same for all oils under a label. Both Widman and Blackstone articles linked above provide examples of that.
I'm not disputing that high ZDP levels effect the cat. I was only was disputing the idea that this combination of additives were eliminated in the mid 1990s. As to the proper quantity for a classic engine, its fair to say that it depends on the engine, its use, and the rest of the oil components.
Let me cite Michael Grant's article because he provides a clear references. I think its as good of a read as Widman's, but with a somewhat different audience and focus.
In reference to real world experience:
There have been increasing numbers of cam/tappet failures, especially in the last four or five years [2004-08]. The Engine Rebuilders Association (AERA) has been keeping records for the last ten years. In that period, there have been more reported cam/tappet failures, with the largest jump in numbers of failures after 2004. Of the failures reported, 25% were traced to poor break-in procedures. The other 75% were traced to use of “modern oil for the break-in.Our own thread to some degree reflects the range of expert analysis. Again Grant
There seems to be a fundamental disconnect here. On the one hand, we have engineers with decades of experience saying modern API SM oil with 0.06 - 0.08% (600-800 PPM) ZDDP should be fine for older flat tappet engines. On the other hand are the large number of companies (with their own engineers) and individuals (many of them respected professional mechanics with decades of real-world experience) who are convinced that 0.06 - 0.08% ZDDP is not enough.My own conclusion is that its not so much one side of the coin versus the other. Rather it is clear that within a certain range ZDP is a proven component to decreasing sliding wear. The question is how much is too little vs too much. Another question is whether there are some oils with effective substitutes. That question I'll mostly ignore because no one here, including me, seems interested in being a guinea pig.
It is worth noting that within the range of ZDP considered effective one of its roles can be suplanted with other additives.
Not all the ZDDP in oil was there to provide anti-scuffing and anti-wear protection. Some of it functioned as an anti-oxidant. This secondary role of ZDDP was taken over by new ashless and phosphorus free antioxidants, which made it possible to eliminate some of the ZDDP.The negatives of
too much ZDDP seems to be fairly well established.
In several reports ZDDP over 0.14% (1400 PPM) is described as providing increased protection against start-up scuffing, and causing increased wear in the long run. And at 0.20% (2,000 PPM), ZDDP will attack the grain boundaries in the cast iron tappets “Once ZDDP levels exceed 1500 to 2000 parts per million, the potential for burned ash accumulations in the ring lands and on the piston domes increases dramatically.”*How Much is Too Little?While that varies with detergent and base stock amongst other factors, GM's study would suggest that 800 ppm would be about the lowest concentration.
Conclusion for entire study: “Within the range of ZDP concentrations evaluated (0.07 to 0.22 weight percent zinc) there was no clearcut effect of ZDP concentration.” **
Also, even with GF-4 max of 800 ppm for some grades, the API SM required more stringent wear tests applicable to flat tappet cams.
Sequence III-G evaluates cam and tappet wear using a GM 3.8L (231 CID) engine that has had the valve train replaced with the flat tappet valve train similar to that used by GM in the 1980s.... Test III-G is specifically “meant to simulate a flat tappet OHV push rod engine in a pickup truck pulling a loaded cattle trailer across the desert on a hot dayThat said, clearly portions of the 1970s GM study and others pointed to something closer to 1200 ppm as appropriate for severe use. Finally, while ZDP is an important consideration, that shouldn't be the only one. Others are deposits (for street oils), getting the correct viscosity for the oil temperature and clearances and cold anti-scuff and extreme pressure additives.
sources cited by
Grant in "Oil for Vintage Sports Cars" for above quotes:
“How Much ZDP is Enough?” R.M. Olree, (GM Powertrain),M.L. McMillan (GM R&D)
SAE Technical Paper Series 2004-01-2986, October 2004"
*“The Lost Lobe Chronicles”, Dave Emanual,
Engine Professional, Jan-Mar 2008
**“Cam and Lifter Wear as Affected by Engine Oil ZDP Concentration and Type”
Loren G. Pless, John J. Rodgers, Fuel & Lubricants Dept., Research Labs, General Motors Corp.
SAE Report 770087, 1977
