Durability characteristics of heavy duty radiators are of ever increasing concern to truck, bus and construction equipment manufacturers. Evaluating life expectancy of heavy duty radiator designs has traditionally involved long and expensive testing procedures. Despite this, final evaluation usually occurs when service problems feed back by owner operators.This paper describes a technique which has been successfully employed, of relative testing, by coupling strain gauge techniques with systems modelling. Relative stress levels in various radiator components can be compared to either existing successful designs or absolute life expectancy estimated using SN curves.The preparation of a tube, critical in determining tube to header joint shear stress is described. The technique can be used to examine design modifications such as header reinforcements or ferrule design and for determining assembly tolerances for manufacturing processing.