Automotive radiator designers require practical design load limits to avoid stress-and stress-corrosion failures under current and anticipated operating conditions. Today, brass radiator materials are evaluated on the basis of coupon corrosion specimens and full-scale engine tests. Coupons provide only limited information while engine tests are time-consuming and costly. An alternative method known as slow strain rate tensile testing provides valid, quantitative information on the performance of radiator materials under controlled conditions that closely simulate radiator service conditions. The test, developed 20 years ago and widely used in several technologies, enables rapid evaluation of radiator materials, coolants and to some extent, radiator fabrication methods. The present paper describes the slow strain rate test and its use in characterizing three common U.S. radiator alloys, two Japanese alloys and one new Olin Corporation alloy in several U.S., Japanese and European coolants over the temperature range from 200-275°F. Materials, coolants, coolant corrosion-inhibitor systems and two lead-based solders are ranked according to their effect on cracking and material properties. Electrochemical data are used to support the findings. The work demonstrates (1) that the slow strain rate tensile test is a useful tool for the rapid and cost-effective evaluation of cooling system components, (2) that new modified brass alloys offer a substantial improvement in crack resistance and (3) that coolants that provide the protection needed under highly stressed operating conditions are currently available.