By William C. "Bill" Anderson, P.E., reformatted for this website and published with the permission of Old Cars Weekly.
In days long ago, there was little question about what oil to use. One used light weight oil in the winter and heavy weight oil in the summer. Then another choice was introduced: detergent or nondetergent.
After further development by the oil chemists, multi-viscosity oils
eliminated the need to change oil weights with the seasons.
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.
In the early 1990s, 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.
The advent of the latest SM type oils have compromised backward compatibility. Generally, it is no longer good practice to use SM marked oils in collector car engines.
Synthetic oils'extended life benefits are of little consequence for most collector car use. Today's synthetic oils are generally not based on the Group IV polyalphaolefin or Group V ester (the original base) since the mid'90s, when a court decision declared the term "synthetic" a marketing term. Thereafter, synthetic oils can be made by hydrotreating petroleum base oils.
Today most synthetics are treated Group II or III petroleum base oils with perhaps a small percentage of Group IV or Group V components.
Engine oil provides a physical barrier (an oil film) that separates moving parts to decrease wear and friction. It also serves as a cooling agent. More than 95% of the oil is base oil, with the rest being a series of additives.
Detergents carry away wear particulates and other contaminants and also assist in neutralizing acids formed by the breakdown of oil and combustion byproducts.
Dispersants control contamination from low temperature operation. Inhibitors control corrosion, rust, and foaming.
Viscosity index improvers control the viscosity of multi-grade oils. Pour point depressants improve cold temperature fluidity.
Antiwear additives make up the difference.
Of primary concern to collector car owners has been the steady reduction in the anti-wear additive ZDDP (zinc diakyl dithiosphosphate) as oil types have evolved from SH to SJ to SL to the
Both zinc and phosphate are key to preventing wear. Unfortunately,
they also contaminate catalytic converters. Oil for collector cars
should have 0.12 to 0.14% (also stated as 1200 to 1400 ppm) of each of the main anti-wear chemicals, zinc and phosphorus as reported in the 1977 SAE technical paper "Cam and Lifter Wear as Affected by
Engine Oil ZDP Concentration and Type." With the SM specification oils, these anti-wear chemicals have been reduced to 0.06 to 0.08% or reductions approaching 50%; the ultimate goal is their complete elimination.
Do not use SM type oils if you regularly drive your Crosley for a few thousand miles. The type of oil is specified in the top half of
the API (American Petroleum Institute) "donut" on each container. Also avoid oils which say "Energy Conserving" in the donut. You can use SM type oil by adding one-half ounce of GM's EOS (Engine Oil Supplement) for each quart of SM type oil installed to improve its anti-wear characteristics. Do not add more; more is not better.
Where "S" and "M" is seen on automobile oils, on diesel oils the same position will say CI-4 where "C" stands for "Commercial" and
"I-4" is the performance level.
Another alternative is to use CI-4 HD oil for diesel engines. These oils have more anti-wear additives. However, be sure to check the container as a new diesel oil, CJ-4, has been introduced to go along
with the new (January 1, 2007) low-sulfur diesel fuel. Given the
preponderance of pre-2007 diesel engines operating, the CI-4 oil should be available for quite some time.
Unless an engine has been completely rebuilt and thoroughly cleaned in the process, do not switch to a synthetic if it hasn't been used in the engine, and do not switch to a detergent-containing oil if only a non-detergent oil has been used.
15W40 multi-viscosity oil imposes no limitation on starting down to 15 degrees F. and provides good protection for hot weather driving.
A couple of Internet links are suggested:
http:/lubricants.s5.com and http://www.Lnengineering.com/oil.html,
first a good overview, and the second more detailed. Though the
second focuses on Porsche engines, the information it contains and the
associated references can be used for all collector cars.