Studebaker Car Club Of New South Wales Inc.







Beware of engine oils for our older technology Engines

Compiled by Steve K.

20th October 2010


This information is a compilation of findings while investigating the most suitable engine oil to use in older motor vehicle engines that have flat tappet technology for valve operation.


The information contained on this page is to help motor hobbyists understand the technology of lubricating oils and their impact when used in our old technology engines.  You are expected to research information to determine what is most suitable for your requirements.


This investigation was triggered when Scott R. broached the subject at our September 2010 General Meeting.

A Bit of Background

These excerpts referenced from "Old Cars Weekly".


"June 23, 2009, by William C. “Bill” Anderson, P.E.
In days long ago, there was little question about which oil to use in cars.

In the “good ol’ days,” hobbyists didn’t have a worry in the world about motor oil.

There were few choices when the 1959 DeSoto Firedome rolled off the assembly line.

Owners used lightweight oil in the winter and heavyweight oil in the summer. Then, detergents were added so another choice was introduced — detergent or non-detergent. After further development by oil chemists, multi-viscosity oils were offered, eliminating the need to change oil weights with the seasons. That situation remained the same into the late 1970s.

The late 1970s saw the introduction of synthetic oils, e.g. Mobil 1, based on Group IV polyalphaolefin or Group V ester, to improve oil longevity. Oil types thereafter remained unchanged for several years. Beginning in the early 1990s, many changes to engine oils have occurred as engine manufacturers and oil industry chemists worked to comply with environmental regulations and to increase fuel mileage. Most of the changes were “backward compatible,” i.e., oils developed for modern engines could be used with older engines for which they were not purposely designed. Some believe the advent of the latest type — with SM marked on the container — compromised backward compatibility.


A little about ZDP
ZDP (Zinc dithiophosphate) in the range of 0.03 percent was first added to engine oil more than 60 years ago to control bearing corrosion.

In the mid 1950s, Chrysler and Oldsmobile engaged in a horsepower race using high-lift camshafts, and both experienced camshaft scuffing and wear problems. These problems were overcome by better metallurgy for camshafts and lifters, phosphating the camshaft and increasing the level of ZDP to 0.08 percent. Another outcome of these problems was the development of a battery of industry-wide “Sequence” oil tests, including tests for valve train scuffing and wear. These tests have continued to evolve and improve ever since.

Some oil suppliers, believing if some ZDP was good, more would be better, added increased levels of ZDP. Unfortunately, we later learned that, with more than 0.14 percent ZDP, long-term wear increased, even though break-in wear was reduced. It was also discovered that at about 0.20 percent phosphorous, the ZDP started attacking the grain boundaries in the iron, resulting in camshaft spalling.

In the 1970s, the ZDP level was set at 0.10 percent phosphorous to take advantage of its antioxidant properties. Increased antioxidancy was needed to protect the oil in Cadillacs pulling big Airstream trailers from thickening to the point of not pumping."


What does it all mean?

It means that modern oils made for modern engines will probably harm our older engines.


What do we do?

We should be using oils and/or additives with sufficient levels of Zinc (Zn, ZDDP/ZDDZ) and Phosphorus (P) to protect our engines.  We need 1200~1400ppm (parts per million).  Too much is also harmful.


There are oils designed for various purposes that could be used.


Oils designed for internal (spark) combustion engines with API codes of "SH" and "SJ" have (at the time of writing) sufficient levels of Zn & P to protect our engines.


Oils designed for diesel engines with API codes of "CJ-4" and "CI-4" also have (at the time of writing) sufficient levels of Zn & P to protect our engines.


CAUTION: Oils designed for use in diesel engines contain detergent, and are, in part, designed to remove sludge and keep the internals clean.  The use of diesel oil in an engine that has not recently been overhauled may cause serious problems in that the detergent will likely loosen any sludge build up inside the engine allowing it to travel around with the oil and potentially block oil ways, resulting in bearing failure.


It is recommended that diesel oils only be used in an engine that has just been overhauled, and/or that is known to be clean and free of any oily build up in the engine.  If detergent oils are used in an old engine containing sludge and other deposits, the detergent action is likely to loosen the sludge/build up allowing to be circulated through the engine which could cause blockages in oil ways, leading to damaged bearings.


The detergent also has the effect of removing the anti-wear films coatings, so low detergent would be better.  Nowhere on the label should the oil say 'for emission system protection' or 'for use in engines equipped with particulate emissions filters'.

This information referenced from LN Engineering website.

The current API standard is SM, and calls for 0.06-0.08% Zn and P.

Here are the running averages for all the oils tested thus far, listed by their API rating:

API P (ppm) Zn (ppm) B (ppm) Mo (ppm) Ca (ppm) Mg (ppm) Na (ppm) Detergents
SE-SJ 1301 1280 151 357 1936 293 214 2443
CI-4 1150 1374 83 80 2642 199   2840
SL 994 1182 133 273 2347 109 22 2479
CJ-4 819 1014 26   2075 7   2082
SM 770 939 127 122 2135 13 139 2287

As can be seen in the above table, the latest API code of SM does not have enough Zn & P to suit our engines, while CJ-4 and SL are a bit light on for Phosphorus.



Vehicles fitted with catalytic converters should note use engine oils with high levels of Zn & P.


This is not a complete list, and if you identify other suitable oils, please advise our webmaster so they may be added.


What can we use in Australia?


At the time of writing, there are a few locally available oils that are rated with the above codes;

Castrol GTX 20W/50, API SJ

Castrol XL 20W/50, API SJ (From label on bottle. Unable to locate data sheet)

Penrite: SHELSLEY MEDIUM, Vehicles 1920 to 1952

Penrite: CLASSIC MEDIUM, Vehicles 1953 to 1966

Shell Helix HX3 20W/50, API SJ/CF




Lucas Heavy Duty Oil Stabilizer < to be confirmed

SLICK® 50 < to be confirmed


If you are interested in reading more on the American Petroleum Institute (API)

"Engine Oil Licensing and Certification System" click >here< to open their PDF file, in a new window.



Bill Cathcart

SDC Forum

Chevelle Forum

Penrite Oil

LN Engineering



Information presented here is a suggestion only, and not necessarily intended to be the correct or only way to carry out a repair.

If you choose to use this information, you do so at your own risk

The SCCNSW, and/or it's members, will not be held accountable for problems that may occur as a result of using this information.

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