For several years now, organic acid based coolants and heat exchange fluids have been introduced on the automotive and industrial market place. The organic acid based coolants provide improved high temperature aluminum corrosion protection and longer drain intervals when compared to traditional coolants.In order to evaluate the organic acid based coolant quality in the field; the end user needs to be able to check several physico-chemical parameters of the coolant. First of all the amount of carboxylate based inhibitors should be determined because the customers can top the system with water. As a result the carboxylates can drop under the minimum required inhibitor level. Secondly, contamination levels from traditional phosphate or borate containing coolants or from the frequently used hybrid coolants-which contain both carboxylates and traditional inhibitors- need to be determined, to give the user an indication about the possible interference of corrosion inhibition technologies used in the examined coolant. Thirdly, the pH of the used coolant provides information on further suitability for use. pH values that are too high or too low may be detrimental to some engine- or heat-exchange system materials. Finally a check on the freezing point of the coolant will provide information on frost protection.In this paper we show the possibilities of an acid-base titration to determine the total carboxylic acid inhibitor content and the presence of contamination in coolants. A refractive index probe is used to measure the glycol content of aqueous coolant mixtures.Further, based on the two above described techniques a user-friendly quality-checking coolant instrument is described which allows measurements of the pH; the contamination level and the total carboxylate based inhibitor content of the test solution. An integrated refractometric determination of the freezing point can also be performed on the same coolant sample.The instrument will allow the user to determine within minutes the essential parameters of an organic acid based coolant on which the user can make well founded decisions on the quality of the coolant at hand.