On operating new trucks in one of the areas of the Egyptian western desert, unexpected fast engine failure occured. Although the technical maintenance to these trucks, was regularly done, the engine failure took place after covering 26000 Km only. In the meantime, no similar failures of trucks operating in other zones have been reported. Therefore, the main reason that led to the engine failure was attributed to the environmental conditions characterised by high dust concentration and relatively high temperature. After reviewing the air and cil filteration systems of the damaged engine and making the necessary inspection and measurements it could be said that the failure occured main-ly due to inefficient oil filteration. A new oil filter, designed by the manufacturer, and the old one have been tested by a special testing rig that has been designed and constructed by the author. Tests on the old and new filters showed that the new one has considerably better performance. In addition, a new engine having the redesigned oil filter has been tested on an engine dynamometer for 400 hcurs. During engine testing, a contaminat dust was added to the oil sump to simulate the actual working conditions, the test results showed no drop in oil pressure and no excessive engine noise which proved the suitability of redesigned oil filter.