>There was a time when filters were not used at all in cars and trucks.
>The motor oils used were of the non-detergent type and did not keep
>dirt in suspension like the detergent oils do. Non-detergent oils allow
>sludge and stuff to accumulate in the oil pan and other areas of the
>motor. The detergent oils keep dirt in suspension so the filter can
trap
>the stuff. If your motor never had a filter, chances are it had
non-detergent
>oil in it. If this is the case and you start using detergent oils, you
will
>probably cause problems when sludge accumulations are loosened and set
>into motion. I don't know if any Jeeps were put into service from the
factory
>without a filter assembly, nor do I know if mil-spec oils used back
then were
>of the detergent type. Maybe someone else can add to this.
Joe's point is entirely valid, the detergent oils were introduced to
MIL-O-2104A in October 1942, the spec being still valid today albeit
suffix D now.
The cross references are contained in the "US and British oil
standardisation agreement" of the above date. They called the detergent
types specifically "heavy" or "high duty" and the SAE reference had H.D.
added.
A CMP F15 manual of the time requires the engine to be flushed out to
remove sludge accumulations before using "the H.D. detergent oils now
coming into service".
Richard
(Southampton UK)
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