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is the neutralization point of the additives. Carbon entering the oil
is dissolved forming a colloid. If the oil is left in the engine until
the additives have been used up or neutralized the carbon starts to
re-deposit on the walls and bottom of the crankcase.
This deposit is a hard flinty granular material. Its effect is
similar to throwing a handful of sand into the crankcase. Anytime
such a deposit is found, the oil should be drained, the crankcase
washed and new oil and filter put in, regardless of lab reports or
length of time the oil has been used.
When oil changes are made on basis of visual inspection and
length of time operated, play safe and change oil if in doubt. The
old saying that oil is cheaper than machinery is still true.
Preventive Maintenance.This is an important although
simple item. It is mainly a case of using common sense. Think of
an engine as a living animal. As a race horse is limbered up before,
then walked until cooled down after the race, so should the engine
be warmed up and cooled off slowly.
There should be no prolonged periods of overload. Keep
only clean oil in the crankcase and keep temperatures up. Watch
fuel mixtures. Watch for and correct minor ailments before they
become major ones.

Diesel engines

There are two distinct types of diesel engines being used in
oil well drilling today. The older is a large heavy-duty engine with
high weight/bhp. The second and newer is the smaller, high com-
pression, high speed diesel such as that of General Motors. The
principal argument in favor of this type of engine is that it is a lot
of power wrapped up in a small package.
The large heavy type is preferred on heavy rigs working on
deep holes. In this kind of drilling, the job lasts a considerable
time, frequently months. Moving the heavier machine is not a
serious problem as moves are not frequent. Being built heavy and

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