The conflicting legislative and performance requirements of the modern automotive engine dictates the detailed optimisation of all features of the design. With this impetus increasing attention is being given to the coolant system where the requirements are for minimum coolant volume and uniform flow distribution.Optimisation of the complex three dimensional coolant system geometry by means of experiment has proven extremely difficult. It is with this background that computational fluid dynamics may prove to have real engineering value providing design solutions that can be incorporated early in the engine design program. A prerequisite however is to demonstrate the accuracy of the analytical technique.This paper describes the comparison of predicted and measured flow fields in a four cylinder engine block. Simple flow visualisation, laser sheet imaging, particle image velocimetry and laser doppler anemometry techniques are used to obtain qualitative and quantitative flow field results.These are compared with simulation. Qualitative and quantitative comparisons are shown to be good with the simulation reproducing all the major recirculations observed.