A simple and compact apparatus, and a method, for determining the characteristics of a number of fluids used in the truck and automotive industries including coolant, bio-diesel, gas-ethanol and diesel engine fluid (DEF). The apparatus includes a sample container providing optical paths of different lengths for making measurements on a sample. The dual path length design allows the apparatus to capture both NIR and UV spectral ranges. The qualitative and quantitative properties of the fluid under test are compared to test results under normal conditions or to the properties of unused fluid. Two light sources are used within a spectrometer with each source being associated with a different optical path length.