Abstract: A solid, water-soluble coolant system treatment tablet for addition to the overflow cannister of an engine coolant system. The tablets are pressed solid cakes including a scale and deposition preventative, a pH buffer, a chemical inhibitor, at least one corrosion preventative, and a binder. The inventive tablets include sodium tetraborate, sodium meta silicate, sodium nitrate, sodium MBT, and for diesel engine use, sodium nitrite.