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safety examinations
Dependent on weather, it takes approximately 6 hours for a hot
engine to return to a cold condition.
Every time you start your engine cold it does the equivalent of
around 800 kilometres of normal hot running engine wear. The
reason is that engine components all expand significantly once they
reach the normal operating temperature.
Engine's moving parts are all made "cold". They are machined to
be slightly smaller than they will be at operating temperature.
With only clearances of a few thousands of an inch (micro
millimetres) separating the components when hot, clearances are
greater on cold starts.
Engine oil provides a film which separates moving parts. The oil
can only do this job when clearances are very close. When the
engine is cold, the clearances are greater and the chance of "metal
to metal" contact is greater.
Oil drains down from cylinder walls during cooling resulting in
pistons and rings travelling up and down rapidly on cylinder walls
with only a slight residual film of oil until proper lubrication
begins. Pistons are machined in such a way as to expand to a near
perfect circular shape when hot from their "irregular" shape when
cold. Until pistons reach normal operating temperature, they are
prone to scuffing wear.
Taxis and other vehicles which run at normal temperature
constantly can travel 4 times the distance of a car doing a lot of
"stop start" running.
Cold running causes more formation of acids and accumulated
effects of moisture in the oil which will evaporate in hot
engines. The result of cold running is that oils will degrade
more quickly over time than engines running at constant
temperatures.
Content courtesy of our friends at Valvoline
oil.
