In order to assess the nature of the problem, a number of experimental data sets were evaluated. Some of them are from literature references 6-8, and some are from our own tests (Figure 3). The analysis shows the degradation rate of engines between on-crank washes, which is mostly due to fouling. The important finding is that neither engine size nor type has a real influence on degradation rate. In particular, the two-shaft engine (two-shaft engines show a higher sensitivity to fouling1) did not behave any worse than the single-shaft engines.