Continental Motors A Series Operator's Manual page 49

1. Starting a Hot Engine. After an engine is shutdown, the
temperature of its various components will begin to stabilize; that
is, the hotter parts such as cylinders and oil will cool, while other
parts will begin to heat up due to lack of air flow, heat
conduction, and heat radiation from those parts of "the engine
which are cooling. At some time period following engine
"shutdown the entire unit will stabilize near the ambient
temperature. This time period will be determined by temperature
and wind conditions and may be as much as several hours. This
heat soaking is generally at the worst from 30 minutes to one hour
following shutdown. During this time, the fuel system will heat up
causing the fuel in the pump and lines to "boil" or vaporize.
During subsequent starting attempts, the fuel pump, (if installed),
will initially be pumping some combination of fuel and fucl vapor.
Until the entire fuel system becomes filled with liquid fucl,
difficult starting and unstable engine operation will be
experienced.
Another variable affecting this fuel vapor condition is the state of
the fuel itself. Fresh high octane fuel contains a concentration of
volatile ingredients. The higher this concentration is, the more
readily the fuel will vaporize and the more severe will be the
problems associated with vapor in the fuel system. Time, heat or
exposure to altitude will "age" aviation gasoline; that is, these
volatile ingredients tend to dissipate. This reduces the tendency of
fuel to vaporize and, up to a point, will result in reduced starting
problems associated with fuel vapor. If the volatile condition
reaches a low enough level, starting may become difficult due to
poor vaporization, since the fuel must vaporize in order to
combine with oxygen in the combustion process.
The operator, by being cognizant of these conditions, can take
certain steps to cope with problems associated with hot
weather/hot engine starting. The primary objective should be that
of permitting the system to cool. Low power settings during the
landing approach will allow some cooling prior to the next start
attempt. Ground operation tends to heat up the engine, therefore,
minimizing this will be beneficial. Cowl flaps (if installed), should
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