Definition of severe duty
It should be in your owners manual.
most all vehicles have a "normal" and "severe" set of service recommendations.
a "normal schedule" for maintenance and a separate schedule for "special operating conditions." If you tow a trailer, use a car-top carrier, idle a lot in stop-and-go traffic or drive frequently in dusty or sandy conditions,:shrug:
Contrary to what you may think, severe duty does not apply only to police cars, cabs, delivery vehicles or other dedicated beasts of burden. It can actually apply to vehicles that aren't driven enough, or are seldom driven at speeds that allow for an engine to heat up to a level where moisture is baked out of the system.
It can also apply to vehicles that operate primarily in heavy stop-and-go traffic that may not log a lot of miles on the odometer, but still have a high level of "engine on" time.
NOTE: Color of used oil was mentioned. Consumer Reports magazine "NYC Taxi" oil study many years ago claimed the color of used oil is an indication of nothing. They tested quality conventional and
synthetic oils and found no difference.
Synthetic oil would be a benefit in extreme cold states like Minnesota for starting. They also claim most people change oil too often.
