Blends of different proportions of straight run naphtha/gas oil and BTX/Gas oil were used in a four-stroke pre-combustion chamber diesel engine in order to illustrate the aspects of performance and thermal loading likely to arise when using syncrudes, multifuel or coal derived fuel. The engine was instrumented for performance monitoring as well as for heat flux and metal temperature measurement and the results were compared with those obtained with gas oil. Correlations were found forthe heat flux level in the cylinder head, piston and cylinder liner with the various blends employed. It was concluded that engines running on syncrudes, multifuel or coal derived fuel shall require greater attention in design and/or development since the higher heat flux prevailing in certain conditions will encourage fatigue induced cracking or liner scuffing. Also the larger heat flux differential across the component will exacerbate the thermal stress problem.