The objective of the project was to equalize the coolant and component temperatures throughout the engine and to eliminate any localized “hot spots”. A designed experiment was conducted to determine the effect of various parameters on the distribution of coolant flow through the internal coolant passage system of a NASCAR Winston Cup racing engine. The recommended configuration which includes internal passage restrictors and external coolant lines considerably reduced the temperature differential throughout the engine and significantly reduced the temperatures of localized “hot spots”. On track testing confirmed the results gathered during the dynamometer testing. The analysis of several engines upon the completion of actual competition validated the effectiveness of the recommended coolant system configuration.