[JJorgensen52]

Originally Posted by So.Cal.Super

As far as the Zinc debate goes.
Zinc has been drastically cut down or almost eliminated from today’s conventional oils due to catalytic converter failure. I would like to know what the conventional oil of the 60’s levels was. For this I have researched and can’t seem to find the Data any more the Hearsay.

Below is some information posted on Jalopy Journal (I've shortened it slightly, posted link to the original), which was taken from Bob Olree, who was a GM Powertrain engineer. The information in the post is taken from a paper he wrote for the SAE (Society of American Engineers). It is SAE document #2004-01-2986 if you are really interested in reading it in greater depth.

Salient point, and the source of my belief that synthetics are fine, are in bold. 0.08% (800ppm) was enough to solve the wear issues that they found in high lift flat tappet cams, and non-performance engines were okay at 300ppm. Since Mobil1 is 800ppm ZDDP, I will continue to run it in all my engines.

In the end, it's just personal preference. I like synthetics because they wear better and have superior performance characteristics over a wider range of temperatures - they also don't generate sludge or break down under heat like dino oil does.

Originally Posted by http://www.jalopyjournal.com/forum/showpost.php?p=3711603&postcount=17

(Bob, who is now retired, was one of GM's Top lubrication engineers)

Engine Oil Mythology
Bob Olree
GMPT – Fuels & Lubes

All of these myths have a common theme; newer oils are bad. And this brings us to the latest myth – new “Starburst”/ API SM engine oils are bad for older cars because the amount of anti-wear additive in them has been reduced. This one has gotten big play in the antique and collector car press lately. The anti-wear additive being discussed is zinc dithiophosphate (ZDP).

Before debunking this myth we need to look at the history of ZDP usage in engine oil.

ZDP has been used for over 60 years as an additive in engine oils to provide wear protection and oxidation stability. Unfortunately, ZDP contains phosphorus, and phosphorus is a poison for automotive catalysts. For this reason ZDP levels have been reduced by about 35% over the last 10-15 years down to a maximum of 0.08% for “Starburst”/API SM oils.

Zinc dithiophosphate was first added to engine oil to control copper/lead bearing corrosion. Starting in 1942, a Chevrolet Stovebolt engine with aftermarket copper/lead insert bearing connecting rods was the standard oil test . The insert bearings were weighed before and after test for weight loss due to corrosion. The phosphorus levels of oils that passed the test were in the 0.03% range.

In the mid 1950s Oldsmobile got in a horsepower war with its Rocket engine against the Chrysler Hemi. Both companies went to high-lift camshafts and both got into camshaft scuffing and wear problems very fast. There were three solutions. Better camshaft and lifter metallurgy, phosphating the camshaft, and increasing the phosphorus level from ZDP up to the 0.08% range. Another outcome was a battery of industry wide “Sequence” oil tests. Two of theses tests were valve-train scuffing/wear tests.

Knowing that this higher level of ZDP was good for flat-tappet valve-train scuffing and wear, some oil companies dumped even more in thinking that they were offering the customer even more protection. However it was soon learned that while going above something like 0.14% phosphorus might decrease break-in scuffing, it increased longer term wear. At about 0.20% phosphorus the ZDP started attacking the grain boundaries in the iron, resulting in camshaft spalling.

Later in the 1970s, the ZDP level was pushed up to the 0.10% phosphorus range as it was a cheap and effective antioxidant, and increased antioxidancy was needed to protect the oil in Cadillacs pulling Airstream trailers from thickening to the point of not pumping. Recently, the need for this higher level of ZDP for protecting the oil from thickening has been greatly reduced with the introduction of more modern ashless antioxidants that contain no phosphorus.

Enough history, now getting back to the myth that “Starburst/API SM oils are no good for older cars. The argument put forth by the myth believers is that while these oils work perfectly well in modern gasoline engines equipped with roller camshafts, they will cause catastrophic wear in older engines equipped with flat-tappet camshafts.


The “Starburst”/API SM oil standards were developed by a group of OEM, oil additive company, and oil company experts. When developing any new engine oil standard the issue of “backward compatibility” always comes up, and indeed the group of experts spent a lot of time researching this issue. Various oil and additive companies ran “no harm” tests on older cars with the new oils. No problems were uncovered.

The new specification contains two valve-train wear tests. One is the Sequence IVA Test which tests for camshaft scuffing and wear using a 2.4L Nissan single overhead camshaft engine with slider finger followers. The wear limits were tightened from the previous oil specification which contained a phosphorus limit of 0.10%. The second is the Sequence IIIG Test which evaluates cam and lifter wear. A current production GM Powertrain 3.8L engine with the valve train replaced with a flat tappet system similar to those used in the 1980s is used. The only reason that this test engine uses this older valve train design is to insure that older engines are protected. All “Starburst”/API SM oil formulations must pass these two tests.

In addition to the protection offered by these two valvetrain wear tests and the new testing which was conducted on the formulations containing lower levels of ZDP, a review of the knowledge gained over the years in developing previous categories also indicates that no problem should be expected. The new “Starburst”/API SM oils contain about the same percentage of ZDP as the oils that solved the camshaft scuffing and wear issues back in the 1950s. They do contain less ZDP than the oils that solved the oil thickening issues in the 1960s, but that is because they now contain high levels of ashless antioxidants that were not commercially available in the 1960s.

Feb 13 2007