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[p76rangie]

Just to post some independent views:

This is a quote from an engineering company dealing with older Porsche engines. It attacks the idea that oil changes should be conducted around the 2500 to 3000 mile mark.

"Failure to use the right oil, use proper filtration, or observe proper changing intervals can affect the performance of even the best motor oil. This also includes changing the oil too often (needlessly bad for the environment and your wallet) or not often enough.  Against conventional wisdom, engine wear decreases as oil ages to a certain extent, which means that changing your oil more frequently actually causes engine wear; these findings were substantiated by studies conducted by the auto manufacturers and petroleum companies, leading to drain intervals increased from 3,000mi/3 months to 5,000-7,500mi/6 months in most domestic vehicles, using mostly non-synthetic oils."

This following article was produced by SAE, you know the people that actually set the oil standards. You should note that the current grade oils must prove that they do not affect wear on flat tappet cams to get the SAE rating. But read an article from the experts on the current oil standards rather than from the chicken littles of this world.

"How about some real facts about Zinc levels from a SAE paper titled "How Much ZDP is Enough?". It is SAE document #2004-01-2986 if you care to locate it and read in greater detail.

Engine Oil Mythology

Myths are ill-founded beliefs held uncritically by interested groups. Over the years there has been an overabundance of engine oil myths.

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 used for the standard engine oil qualification test. The insert-bearings were weighed before and after test to evaluate weight loss due to corrosion. The phosphorus levels of oils that passed the test were in the 0.03% range.

In the mid-1950’s, Oldsmobile got into a horsepower war between its Rocket engine and 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: 1) better camshaft and lifter metallurgy, 2) phosphating the camshaft, and 3) increasing the phosphorus level from ZDP up to the 0.08% range. In addition, the industry developed a battery of oil tests (“Sequences”), two of which 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, thinking that they were offering the customer additional protection dumped even more into the oil. It was soon learned, however, that, while going above about 0.14% phosphorus might decrease break-in scuffing, longer-term wear increased. Further, at about 0.20% phosphorus, the ZDP started attacking the grain boundaries in the iron, resulting in camshaft spalling.

In the 1970’s, the ZDP level was pushed up to the 0.10% phosphorus range because it was a cheap and effective antioxidant. The increased antioxidancy was needed to protect the oil in Cadillacs pulling Airstream trailers from thickening to a point where the engine could no longer pump it. Recently, the need for this higher level of ZDP to protect the oil from thickening has been greatly reduced with the introduction of modern ashless antioxidants that contain no phosphorus.

Enough history. 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” is always of great importance. Indeed, the group of experts spent a lot of time researching this issue. In addition, multiple oil and additive companies ran “no harm” tests on older cars with the new oils; no problems were uncovered.

Beyond the “no-harm” testing, the new “Starburst”/API SM specification contains two valve-train wear tests. One is the Sequence IVA, which tests for camshaft scuffing and wear using a 2.4L Nissan single overhead camshaft engine with slider finger followers. The wear limits for this test were tightened from those of the previous oil specification, even though the old spec had a higher, 0.10%, phosphorous limit. The second test is the Sequence IIIG, which evaluates cam and lifter wear. For this test, a current-production, GM Powertrain 3.8L engine with the valve train replaced with a flat-tappet system, similar to those used in the 1980’s, is used. The only reason for using this older valve-train design is to ensure 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 valve-train wear tests and the “no-harm” testing, a review of the knowledge gained over the years in developing previous categories also indicates that no problem should be expected. For example, 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 1950’s. They do contain less ZDP than the oils that solved the oil thickening issues in the 1960’s, but that is because they now contain high levels of ashless antioxidants, which were not commercially available in the 1960’s.

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 a problem. The legendary Smokey Yunick wrote that his solution to the problem was to buy multiple camshafts and simply try them in a slave engine 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. "