[AT] Using modern oil in old engines

[Mike Sloane]

For several years I have been watching the ongoing fuss about which oil 
to use in which antique tractor engine. I just kept on using NAPA diesel 
rated "Fleet" oil in everything. This was posted on another list, and I 
am just passing it along exactly as it was presented:

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Wrong totally wrong. One of THE reasons motors last longer now is oil
improvments. Modern oils will help if you use the proper grade… hands
down. As a mater of fact the
I pull oil samples and test them BEFORE changing oils and can add
additives as needed. Also test them on fleets and before buying
equipment. I also worked for custom oil blender…Check the specs guys
your perpetuating a myth.
An ASE Master tech…
http://www.cadillacforums.com/forums/northstar-performance-technical-
discussion/125545-engine-oil-myths-including-zdp-gm.html
The Starburst Oil Myth — The latest myth promoted by the antique and
collector car press says that new Starburst/ API SM engine oils
(called Starburst for the shape of the symbol on the container) are
bad for older engines because the amount of anti-wear additive in
them has been reduced. The anti-wear additive being discussed is zinc
dithiophosphate (ZDP).

Before debunking this myth, we need to look at the history of ZDP
usage. For over 60 years, ZDP has been used as an additive in engine
oils to provide wear protection and oxidation stability.

ZDP was first added to engine oil to control copper/lead bearing
corrosion. Oils with a phosphorus level in the 0.03% range passed a
corrosion test introduced in 1942.

In the mid-1950s, when the use of high-lift camshafts increased the
potential for scuffing and wear, the phosphorus level contributed by
ZDP was increased to the 0.08% range.

In addition, the industry developed a battery of oil tests (called
sequences), two of which were valve-train scuffing and wear tests.

A higher level of ZDP was good for flat-tappet valve-train scuffing
and wear, but it turned out that more was not better. Although break-
in scuffing was reduced by using more phosphorus, longer-term wear
increased when phosphorus rose above 0.14%. And, at about 0.20%
phosphorus, the ZDP started attacking the grain boundaries in the
iron, resulting in camshaft spalling.

By the 1970s, increased antioxidancy was needed to protect the oil in
high-load engines, which otherwise could thicken to a point where the
engine could no longer pump it. Because ZDP was an inexpensive and
effective antioxidant, it was used to place the phosphorus level in
the 0.10% range.

However, phosphorus is a poison for exhaust catalysts. So, ZDP levels
have been reduced over the last 10-15 years. It's now down to a
maximum of 0.08% for Starburst oils. This was supported by the
introduction of modern ashless antioxidants that contain no
phosphorus.

Enough history. Let's get back to the myth that Starburst oils are no
good for older engines. The argument put forth 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 facts say otherwise.

Backward compatability was of great importance when the Starburst oil
standards were developed by a group of experts from the OEMs, oil
companies, and oil additive companies. In addition, multiple oil and
additive companies ran no-harm tests on older engines with the new
oils; and no problems were uncovered.

The new Starburst specification contains two valve-train wear tests.
All Starburst oil formulations must pass these two tests.

- Sequence IVA tests for camshaft scuffing and wear using a single
overhead camshaft engine with slider finger (not roller) followers.

- Sequence IIIG evaluates cam and lifter wear using a V6 engine with
a flat-tappet system, similar to those used in the 1980s.

Those who hold onto the myth are ignoring the fact that the new
Starburst oils contain about the same percentage of ZDP as the oils
that solved the camshaft scuffing and wear issues back in the 1950s.
(True, they do contain less ZDP than the oils that solved the oil
thickening issues in the 1960s, but that's because they now contain
high levels of ashless antioxidants not commercially available in the
1960s.)

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 probably
take 60 or 70 years for this one to die also.

Special thanks to GM's Techlink
- Thanks to Bob Olree – GM Powertrain Fuels and Lubricants Group
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Mike