- In the mid 1930's the Diesel engine, which formerly was used only as a large, low-speed machine, was developed into a smaller
high-speed engine for use in trucks, busses, and tractors. Along
with these changes in mechanical design came many problems, of
which a major one was lubrication. Because ordinary mineral lubricating
oils quickly deteriorate, certain chemical compounds were
mixed with the oils to improve their performance. Introduction
of the chemical additives to the Diesel engine lubricants met with
considerable success and the practice was soon followed in spark-ignition
The additives used now include such chemical compounds as
anti-oxidants, anti-corrosive agents, extreme pressure agents,
viscosity index improvers, and pour point depressants. In addition
to the compounds developed by petroleum and chemical companies,
other commercial addition agents, which are sold in auto supply
stores and service stations, have appeared with many and varied
claims. Today there are many of these "patent medicine" mixtures
on the market.
The purpose of this investigation was to determine the
stability of a representative group of these commercial addition
agents in an internal combustion engine. A small single cylinder,
water-cooled Lauson was used as the test engine. It was mounted
on a test stand with a direct current generator and a control panel.
The procedure followed in the tests was adapted from the
Coordinating Research Council Handbook. It consisted of a
standardized break-in period with a reference oil, and a test time
of 36-hours with an additive-reference oil mixture. The reference
oil, of high rating, was procured from the Coordinating Research
Council for the control in these tests. The oil or additive
mixture, after the 36-hour test period, was analyzed by the following
ASTM tests: Gravity, viscosity at 100 F and 210 F, flash and
fire points, water and sediment, neutralization number, precipitation
number, and copper strip corrosion. Photomicrographs were taken to observe the extent of corrosion on copper-lead bearing sections, cut from a bearing whose composition was 65 per cent
copper and 35 per cent lead. These specimens had been present in
the sump during the test run.
Two different oil temperatures were utilized to obtain extremes
in operating conditions. One oil temperature was 212 F
and the second at 110 F, with 25 ml of water added to the crankcase.
The first value simulated long, hot weather, driving conditions
and the second town driving with many starts and stops and
low oil temperature.
The results of the tests are summarized as follows:
1. The addition of water to the crankcase accelerated
the deterioration of the additive-reference
2. There were definite tendencies in most additives
to corrode the copper-lead bearing strips.
3. The additives did not prevent carbon deposits or
sludge formation to any greater degree than the
4. All of the additives had a definite effect on the
physical properties of the reference oil.