The airflow through a truck engine compartment consists of a complex system of series and parallel flow paths. This system can be modeled in terms of a network of equivalent ductwork elements. The detailed description of engine compartment airflow provided by this model can be used as a means of predicting the effect of acoustical engine enclosures when the ductwork element parameters are altered. The initial implementation of this model will require the performance of a number of component and truck wind tunnel tests; this data should be obtained to permit the use of the model. In-service monitoring of either engine or gearbox temperature performance requires the recording 8 to 10 parameters plus clock time for an adequate description of vehicle behavior. This monitoring should be initiated at the initial vehicle startup and continued throughout the day, including periods of engine shutdown. A total daily test period of approximately 10 hours is expected. The sampling data rate of 1/min for each parameter is sufficient for monitoring purposes. This monitoring requirement can be met by a relatively inexpensive data logger plus suitable transducer signal conditioning.