Engine Oil
Everyone is familiar with engine oil; however, not all are familiar with
the basic ingredients. How the product is produced and what can make
one oil different than another.
Motor oil is composed of two basic ingredients, base oil and additives.
Base oil is the primary ingredient, (about sixty percent), of the finished
product and does the most to provide a protective lubricating film between moving engine parts. Most the additives perform the important function of protecting the base oil from deterioration and decomposition caused by
the harsh environment inside the engine. Also important is keeping those contaminants not filtered, in suspension until the oil is drained.
Base oils are refined from crude oil. Contaminants such as sulfur, nitrogen
and unsaturated hydrocarbons must be removed during the refining process.
How well these are removed make a big difference in the quality of the finished product. Even small amounts can allow excess oxidation or breakdown of the base oil; no matter how many anti-oxidants are added.

Synthetic Engine Oil:
   
Synthetic engine oil has overcome some of the problems of crude based
oils. It is possible to extend the change intervals with synthetics; however,
unless you have some means of measuring the acid and suspended contaminant level of the oil, it may be a good idea to use a good premium engine oil instead.

Oil Change Intervals:

We feel that the engine oil and filter should be changed four times a year.
Each three months. The rational being that vehicles driven on short
trips, parked for awhile and driven again for a short distance promote the formation of moisture, sludge and acid in the crankcase. The oil in engines of  vehicles driven more miles 'boil out' most of the moisture. Changing oil by how many miles are driven may not be the best gauge to use.