Today’s modern engines are exposing engine coolants to more severe operating conditions involving higher coolant temperatures, greater heat rejection requirements, greater metal to coolant heat fluxes, higher coolant flow rates, higher cooling system pressures, and slower deaeration. These conditions will have a tendency to accelerate oxidation/thermal degradation, reduce corrosion protection, and shorten coolant life. In efforts to simulate the increased severity in operating conditions, an accelerated oxidation and corrosion test, using a rotary pressure vessel oxidation test, was developed and evaluated to assess the oxidation/thermal stability and corrosion protection of conventional, hybrid, and extended life coolants. The test involves exposing the coolant to a high temperature oxygen rich environment under pressure with six different metal corrosion coupons. The test allows a quantitative assessment of corrosion protection of the coupons and the effects on coolant chemistry. Test results are provided on conventional, hybrid, and extended life coolants. The test has also been found to be a promising predictive tool to screen satisfactory versus unsatisfactory coolant formulations, including recycled coolants.

Multi-vehicle or universal coolants, or both, have been introduced into the marketplace to satisfy the wishes of mass merchandisers, automotive garage and repair shops, quick oil change establishments, and the general public for a convenient single coolant for use in the myriad makes and models of vehicles. Universal coolants are recommended for top off, as well as complete drain and fill of the customer’s cooling system, regardless of the color or inhibitor chemistry of coolant already in use. Coolant mixing, and potential compatibility issues, will result for the top-off scenario, but may also be of concern following coolant system flush-and-fill. However, there are currently no standard compatibility tests to define satisfactory compatibility when coolants of different chemistry are mixed. Previous work to establish compatibility of coolant mixtures documents that potential coolant deterioration of the corrosion protection may occur in the ASTM D 4340 [1] Aluminum Heat-Rejection Test when mixing coolants with different additive chemistries. Compatibility testing has been conducted on various universal coolants with traditional high silicate, traditional low silicate, hybrid (phosphate free), hybrid (phosphated), and OAT-only technologies. This paper provides results of the coolant compatibility tests and correlation of coolant chemistry with coolant performance in these tests.

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