The purpose of this study to investigate, how third year mechanical engineering students are able to use their knowledge of concept maps in their study of the topic of "Introduction to the Internal Combustion Engines (IICE)". 41 students participated in this study. Firstly, the students were taught about concept maps and then asked to draw their concept map of the topic IICE. Afterwards, two achievement tests were administered. One test, namely, knowledge applications test (KAT) included questions on the application of knowledge of the topic of IICE and other test, knowledge recall test (KRT) contained the questions that require a recall of knowledge of the topic of IICE. The students' concept maps were scored by comparing with the expert map created by the teacher. The correlation between concept map scores (CMS) and the scores in tests which measure application of knowledge (KAT) was moderate while the correlations between score of concept map and the test that measures a recall of knowledge (KRT) was weak. While achievement tests measure knowledge in different context, CMS, on the other hand, measures knowledge about related concepts and relationships among concepts. As a result, concept maps can be used as a supplementary assessment method along with achievement tests. Most of the students were satisfied with use of concept mapping in the topic of internal combustion engine. They indicated that concept mapping helps them to understand the key concepts, to connect the various concepts with each other and to correct misconceptions.