Soot particulate matter deposition on the tubes of exhaust gas recirculation (EGR) coolers would form an insulating deposit layer, which deteriorates the thermal efficiency of the cooler and increases the pressure drop substantially. The objective of this research is to examine the influence of using helical tubes instead of straight horizontal tubes on the development of deposit layer. An experimental setup has been designed and constructed to examine the thermal performance of different types of EGR coolers under both clean and fouling conditions. Two sets of experiments have been performed, i.e. with and without soot particles, and in each set three types of EGR coolers have been examined, namely straight tube cooler, and two helical tube coolers of 5 and 10 windings. The effectiveness of the helical tube cooler is highest in case of 10 windings and lowest in case of a straight tube cooler which is due to the increase in the heat transfer surface area. The thermal resistance of the fouling layer in case of a straight tube cooler and 10 windings cooler has stabilized, however the thermal resistance in case of 5 windings is not stable and it is increasing with time. It has been concluded that there is a cleaning action during the fouling experiment in case of the helical tube coolers, and that is due to the secondary flow, and the efficiency of cleaning is a function of the intensity of the secondary flow. The thermal performance of the 5 windings cooler is not stable due to the development of the fouling layers, while in case of the 10 windings is stable, and that means there is a critical number of windings for the helical tube EGR coolers above which fouling diminishes. This critical number of windings is a function of the gas speed, particles size, tube diameter, radius of curvature and the winding pitch. The secondary flow in helical tubes agitates the boundary layer and decreases the pressure drop, such that it is advised to use helical tube coolers with more windings from a thermal and a fluid mechanics point of view.