Motoring Notes
| Date | 01 April 1978 |
| Published date | 01 April 1978 |
| Author | Paul Harris |
| DOI | 10.1177/0032258X7805100205 |
| Subject Matter | Article |
SUPERINTENDENT
PAUL
HARRIS
A von and Somerset Constabulary
Motoring Correspondent
of
The Police Journal
MOTORING
NOTES
Synthetic Oils
Engine lubricants, whether they are oils, greases, semi-solids like
graphite and molybdenum disulphide, or synthetic based products,
have one common primary role. They have to interpose themselves
between metal surfaces so that these can moverelative to each other
without actually touching. The lubricants become in effect millions
of microscopic ball bearings, rolling instead of rubbing.
This would
not
be too onerous atask for any reasonably stable
liquid if engines always
ran
at constant moderate speeds under
constant loads and under temperate ambient conditions. In practice,
speeds, bearing loads and operating temperatures vary enormously
even under normal motoring conditions. Seasonal changes in
ambient temperatures can create quite artificial variations in the
state of the lubricant. Perhaps the most extreme example of this
demand for consistency in lubricant performance under wide
variations of temperature was that of Concorde. Its engines had to
meet extremes of 200°C (twice the boiling point of water) whilst the
surrounding air temperatures was as low as
-40°C.
This target was
met by a synthetic hydrocarbon product.
No car has to meet such extreme demands, but the requirements
of modern car engines can be quite tough on lubricants. Every year
sees increases in power output relative to capacity and weight with
consequent additional bearing loads and higher operating tempera-
tures. Many modern cars already experience sump temperatures as
high as 150°Cand engine designers are constantly looking for greater
efficiency. The engines of tomorrow will be required to economise
on fuel, will run hotter to combat pollution problems and will make
greater use of light alloys to improve power/weight ratios. It is
expected that such trends will lead to design increases in sump
temperatures of 10 to 15°C over the next few years. All of these
factors tend to reduce the ability of a lubricant to perform its
secondary role as a coolant. Oil circulated around hot bearings, the
very hot valve gear and the even hotter pistons and rings returns to
the sump where it has a short time to cool off before being pumped
round again. A large sump might seem to be a simple answer, but
there are snags. Apart from the important space and weight con-
siderations involved, over-cooling could be a serious disadvantage
in winter conditions. The oil would be too thick to circulate freely;
191 April 1978
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