With the recent shortage and higher cost of new antifreeze and the disposal problems of used engine coolant, the interest in recycling the used engine coolant has sharply increased. Various methods have been proposed to reclaim used coolant for reuse in engine cooling systems. The coolant reclaiming methods include various filtering processes and full distillation of the water and ethylene glycol from the coolant. The ethylene glycol is that part of antifreeze which provides low temperature freeze protection. The commercial antifreezes contain ethylene glycol and various chemical inhibitors to prevent corrosion and damage to surfaces in cooling systems.
The full distillation procedure is the only method acceptable by Caterpillar to reclaim the used coolant. The ethylene glycol and water obtained from this process can be treated with new chemical corrosion inhibitors to provide a like-new coolant.
Throughout the normal life of a diesel engine coolant, supplemental corrosion inhibitors are added periodically. These chemicals are dissolved in the water part of the coolant mixture. During the normal life of the coolant mixture, the water will continue to hold these chemicals in solution until the saturation point is reached. At this point, the coolant should be replaced.
NOTE: Based on Caterpillar’s recommended rate of adding corrosion inhibitor, normal coolant life is 3000 hours or 2 years, whichever comes first. On-highway truck engine mileage for coolant change will vary depending on the average miles per hour accumulation.
Filtering methods for reclaiming the used engine coolant do not reduce the level of chemicals in the water. The already chemically-saturated water is put back into the engine. As new corrosion inhibitor is added to this chemically-saturated water, it cannot go into solution with the water. The corrosion inhibitor will remain in the solid state. This causes detrimental effects because deposits form on heat transfer surfaces, clog flow passages, and get between water pump seal faces.
Therefore, the distillation method is the only effective method to reclaim used engine coolant. The “pure” ethylene glycol and “pure” water are boiled out of the used coolant and then condensed back to a liquid for reuse. All the chemical additives and corrosion/erosion products from the cooling system remain as a residue in the distillation process. This solid residue which is about 10% of the volume of the initial used coolant remains for disposal as waste.