The objective of this study was to develop an additive package that would allow the continued use of MIL-A-46153 antifreeze after its inhibitor system reached a marginal condition. Since Military Specification for Antifreeze, Ethylene Glycol, Inhibited, Heavy-Duty, Single-Package (MIL-A-46153) is a composition specification with a well documented history, a field test kit is used to determine when the antifreeze should be replaced. Eighteen different formulations were screened in ASTM Corrosion Test for Engine Coolants in Glassware (D 1384) with used MIL-A-46153 antifreeze which contained depleted inhibitor ingredients. Two formulations were selected for final testing. Both formulations were similar except that in one sodium silicate was used and in the other, potassium silicate. The formulation with sodium silicate was dropped from further testing when it was discovered that upon sitting for a period of one month the material formed a precipitate. The precipitate does not form in the formulation using potassium silicate.

Results of ASTM D 1384 test and ASTM Method for Simulated Service Corrosion Testing of Engine Coolants (D 2570) show that the formulated additive package used at a 3% concentration in used antifreeze not only gives adequate protection to the six cooling system metals, it is an excellent inhibitor for water. It can also be added to new MIL-A-46153 antifreeze with no deleterious effects. Several military vehicles were selected for a one-year field test and the pH and reserve alkalinity were monitored throughout the test at three-month intervals. The results show that the pH and reserve alkalinity remained at an acceptable level over the one-year period and clearly indicate the coolant was still useable for further service.

It is concluded that the addition of the additive package, Additive, Antifreeze Extender, Liquid Cooling System (MIL-A-53009), to used military antifreeze will allow continued use for a period of time exceeding one year. It has no adverse effect if added to a new fully inhibited antifreeze and is an excellent inhibitor for a water system.