05-02-2012, 07:01 PM
Join Date: Mar 2011
ZDDP "Devils Advocate"
Here's a pretty cool article I found written by Bob Olree. This one may have been discussed in the past but I haven't seen it before and found it very interesting as "we" talk about ZDDP being a "must" in our flat tappet engines. Yet, I have never heard of any first hand reports of a cam going south specifically due to zinc/phos....or lack there of.
Apparently Mr. Ogletree is a retired lubrication engineer @ GM.
Engine Oil Mythology
GMPT – Fuels & Lubes
"Myths are ill-founded beliefs held uncritically by interested groups. Over the years there has been an overabundance of engine oil myths. One was that the only good oils were oils made from “Pure Pennsylvania Crude Oil.” This one got started before the Second World War when engine oil was crude oil with very minimal refining, and crude oil from Pennsylvania made better engine oil than Texas or California crude. With modern refining, almost any crude can be made into good engine oil.
The next myth was that “modern” detergent engine oils were bad for older engines. This one got started after the Second World War, when the government no longer needed all the detergent oil for the war effort, and it hit the market as Heavy-Duty oil. These new detergent oils gave the pre-war cars, which had been driven way past their normal life and were full of sludge and deposits, a massive enema. In some cases bad things happened such as increased oil consumption – the piston rings were completely worn out and the massive piston deposits were the only thing standing between merely high and horrendous oil consumption. If detergent oils had been available to the public during the war, this myth never would have started.
Amazingly there are still a few people today, 60 years later, who believe that they need to use non-detergent oil in their older cars. Apparently it takes about 75 years for an oil myth to die.
Then there is the myth that new engines will not break-in on synthetic oils. Apparently there was an aircraft engine manufacturer who once put out a bulletin to this effect. Clearly the thousands and thousands of cars filled with Mobil 1 as factory-fill, which have broke-in quite well, should have put this one to rest. However this one is only 40 years old, so it has another 35 years to live.
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.
The oil’s ZDP level is only one factor in determining the life of an older camshaft or a new aftermarket camshaft. Most of the anecdotal reports of camshaft failures attributed to the newer oils appear to be with aftermarket camshafts. Breaking in extremely aggressive aftermarket camshafts has always been problem. The legendary Smokey Yunick wrote that his solution to the problem was to buy multiple camshafts and simply try breaking them in until he found one that survived break-in without scuffing.
Despite the pains taken in developing special flat tappet camshaft wear tests that these new oils must pass and the fact that the ZDP level of these new oils is comparable to the level found necessary to protect flat tappet camshafts in the past, there will still be those who want to believe the myth that “new oils will wear out older engines.” Like other myths before it, history teaches us that it will take about 75 years for this one to die also."
72 Scout II - Flame Red
Built 304/TBI-7747/727-TF2/D20-Twin stick