Starting from 2020, TAN analysis will be performed according to the ASTM D8045, a more reliable and repeatable method.

The continuous improvement strategy that Mecoil has undertaken since the very beginning, dedicating to oil analysis and predictive diagnosis, requires the adoption of the latest technologies, giving priority to reducing the environmental impact of test methods and pratical aspects of lubrication management.

With such perspective, starting 2020 acid number testing on oil samples will be performed using an updated technique in compliance with the international standard ASTM D8045 (thermometric determination), maintaining the same economic conditions agreed for the “historical” procedure ASTM D664 (potentiometric method). The updated procedure is a more reliable method (faster and more robust) compared to traditional ones, especially for engine oil analysis, and performs comparably for industrial, mineral and synthetic lubricants (turbine, hydraulic, gear oils, etc). Chemical reactions, reagents and solvents of these two methods are the same, but titration endpoint detection is modified: the new thermometric method uses a highly accuracy temperature sensor for detecting the endothermic reaction of the indicator. The latter has been selected to obtain comparable results to the reference methods, potentiometric ASTM D664 and colorimetric ASTM D974, but using a more reliable technology and not negatively influenced by sludge, insoluble, detergent additives and sample colour. The results of the new procedure will therefore be equivalent to the historical ones obtained with the previous method, as established by various correlation studies (see Bibliography), also performed in the Mecoil laboratory on new and used lubricants. So far, it will be possible to keep the established analytical trends and limits, for an immediate and optimum perception of “conditions monitoring” (lubricants’ and machines’ health state) at your plant.

Acidity number: repeatability performance in engine oil analysis


Laboratory Manager
Alessandro Paccagnini, CLS MLT-1


[1] C. Haider, T. Smith “Fully automated determination of TAN and TBN by thermometric titration – fast and reliable” – Oildoc Conference 2013.
[2] D. Murray “TAN Thermometric Method Evaluation” – Canadian Crude Quality Technical Association Project Report, April 2014.
[3] G.B. McGarvey, C.E. McGarvey, B. Thakkar, L. Carey, S. Kappes “Controlling Corrosion: a new method to measure the acid number in crude oil and refinery distillation fractions” – Petro Industry News, Oct-Nov 2016
[4] M. Mattiolo “Determinazione del Numero di Acidità mediante Titolazione Termometrica” – Metrohm Italiana, 2016

Mecoil’s strategy is continuous improvement