TECHNICAL SERVICE BULLETIN 94-1
Automotive Oil Change Intervals
Severe vs. Normal Driving
Revised October 2013
Page 2 of 3
rather than the "normal" and "severe" titles used in the owners' manuals. Since
80 percent of motorists drive under less than ideal conditions, the "average" title
is certainly justified.
Severe (or average) service, as defined in most owners' manuals, includes trips
of less than four miles (six km), particularly in cold weather. Under these
conditions, the engine does not warm up completely, causing moisture to
accumulate in the crankcase. Every time the engine is started, the oil is
contaminated with blow-by soot, raw gasoline and condensed moisture. Unless
the engine gets regular extended highway travel, these contaminants remain in
the oil.
After 3,000 miles (5,000 km) of "severe" - or "average" - driving, the oil can be
saturated with foreign substances. Within the same time period, chemical
detergents, dispersants, anti-oxidants, viscosity improvers, and corrosion
inhibitors may be depleted. Although the oil does not wear out, the additives do.
Unless they are replenished, the oil cannot properly function in today's internal
combustion engines.
Trips of less than four miles (six km) is the key factor in keeping most motorists in
the average or "severe" category. In many owner's manuals the following are
considered "severe" or average conditions:
Frequent idling for long periods of time, such as stop-and-go driving in
heavy traffic. Many vehicles are subjected to this condition twice a day
in commuting to major cities.
Sustained highway driving in hot weather, such as vacation travel.
Towing a boat or trailer, carrying heavy objects on a rooftop rack.
Driving in dusty conditions, such as dirt or gravel roads.
Prolonged operation at sub-zero temperatures.
Driving on steep hills or mountains on a regular basis.
Bear in mind that any one of the above conditions can make it mandatory to
change oil and filter at 3,000 mile (5,000 km) or three-month intervals.
If one does not know which kind of driving, average or ideal, they do the most,
we recommend changing at average intervals. Like most preventive maintenance
the oil and filter change is a form of insurance. In addition to the contaminants
produced by engine operation, dirt can get into the crankcase and metal particles
can flake off internal engine parts and bearings. The purpose of the oil change is
to remove the harmful contaminants that have accumulated in the crankcase and
to replace the depleted additive package in the used oil.
The oil filter should be changed every time the oil is changed because up to 3/4
of a quart (3/4 of a liter) of used oil remains in the filter when only the oil is
changed. This contaminated oil immediately mixes with the clean oil and