Coolant containing the proper amount of glycol and additives is critical to the reliability and durability of heavy duty diesel engines. Occasional coolant analysis is required in the field to insure that the proper coolant composition is maintained, otherwise severe engine damage can occur. There are several types of coolant test kits currently available in the field as well as commercial coolant analysis services. Some of the test methods used provide information that does not predict or correlate with a coolant's capability to prevent system corrosion and deposit formation.This paper examines the more widely available field coolant analysis methods and documents their strengths and weaknesses. Further, recommendations are made as to acceptable laboratory methods for the analysis of engine coolants.