COLOR:
- Does not accurately predict oil condition

SMELL:
- Does not accurately predict oil condition

VISCOSITY:
- A significant increase could indicate oil failure
- Synthetic oil viscosity does not increase as much as petroleum oil viscosity
as is oxidizes
- Diester and coolant oils viscosity do no tend to increase significantly with
oxidation

TOTAL ACID NUMBER (TAN):
- Measures acid level in oil
- Best method of determining oil condition.