In summary, the demands made on the oil are draining (no pun intended). The
oil eventually loses its ability to lubricate, clean, and flow freely. Each function
is extremely important to the performance and life of the engine.
There are three characteristics to evaluate when checking automotive fluids:
color, consistency, and smell.
Color
Healthy oil is caramel colored and translucent, indicating that there is little dirt
in the oil and that it has not been overheated. A dark brown or black color
indicates the presence of dirt or overheating of the engine. Intense heat actually
boils the oil and destroys its chemical fortifiers. As a result, the oil loses its
viscosity (ability to flow and adjust rate of flow to temperature change), its
lubricity, its ability to protect against chemical contamination, its ability to
absorb heat, and its rust-inhibiting quality. This puts the engine at risk for
premature engine damage. Upon inspection, if the oil is a milky color it means
there is moisture in the oil. It got into the oil through the cooling system or from
the outside. In either case, you must find the source and do the required repair
immediately before major engine damage occurs.