A highly accurate analysis test kit on board for total iron content in the scavenging drain of diesel-powered main engines. The colorimetric method enables crew members to take extremely accurate analysis of total iron content by specific wavelength filter for a photoelectric colorimeter and a special mix of two kinds of Reagents (A & B). The result is displayed in parts per million(PPM) value. Optimizing scavenging drain oil requires careful monitoring of conditions inside the diesel main engine and recently, many instances of low-temperature sulfuric acid corrosion have been reported due to an increase of design pressure inside the cylinders. This analysis kit can measure not only conventional magnetic iron particles, but also the total iron content including iron ions, which lead to earlier detection of abnormalities inside the cylinder.