Corrosion protection is essential to any engine coolant. The wide range of metals and materials utilized in automobile engine cooling systems requires a complex of additives for corrosion resistance. A basic understanding of corrosion mechanisms and influences of individual metals is fundamental to successful formulation. Several types of corrosion can occur and these are addressed by different ASTM engine coolant testing methods. The desire for longer-life coolants emphasizes the need for newer testing methods to successfully simulate engine coolant requirements. Extension of current methods and new approaches to providing protection is discussed.
A dynamic test for soldered joints in a coolant environment has been developed that allows definitive coolant comparison with respect to soldered joint response in service. The test unit consists of a heated pressure vessel, capable of handling temperatures up to 149°C and pressures up to 0.21 MPa, and twelve specimen jigs. Soldered joints are made under controlled conditions and exposed in coolant under static and dynamic stress rupture conditions. Joint failure is measured on timers that trip upon specimen fracture. Solder alloys selected for the program were 70Pb-30Sn, 95Pb-5Sn, and 97Pb-2.5Sn-0.5Ag materials. Four commercially available coolants were tested with the above solders at selected loads. A series of tests was also conducted to examine the effect of water used in diluting the coolant. Different commercial coolant and water combinations were found to produce variable degrees of corrosion and joint failure. Solder bloom was found to increase in engine coolant at radiator operating temperatures in the presence of applied stresses.
Methods and equipment for engine coolant testing are described covering some of the newer standard procedures and proposed additions to the tests used. Methods and equipment gradually evolve according to the needs of the automotive industry. A continuous process is involved in design, safety, operator convenience and test requirements. The ASTM D 4340 test equipment with improvements is discussed. The ASTM D 3147 stop leak test has been substantially revised and updated. A new hot surface scale deposit test procedure and equipment are presented. The ASTM D 2809 test is reviewed with commentary on the current test procedure. Simulated service testing for long-life coolants requires changes to the present D 2570 standard, with consideration of including a more dynamic test similar to European approaches.
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Durability of aluminum alloy automotive radiators in service depends on the alloy selected and the expected engine coolant environment. The challenge is to find testing methods that correlate with service experiences that allow for comparative evaluation of competing materials without resort to long-term vehicle exposure at initial selection stages. Design, manufacture, and processing affect radiator performance and must be taken into account in corrosion testing. Aluminum alloys AA3003 and AA7072 are used to illustrate the test program. Electrochemical corrosion test methods were used for screening purposes in alloy selection and corrosion test environment studies. A simulated service test method is used with selected corrosion media to provide accelerated corrosion data in full sized radiators. The importance of relating corrosion test media to ultimate engine coolant use and abuse is covered. Methods have been correlated with field tests to prove the approach used.
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