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In the early years of antifreeze/coolants (1920s & 30s) glycerin saw some usage, but because of higher cost and weaker freeze point depression, it was not competitive with ethylene glycol. Glycerin is a by-product of the manufacture of biodiesel (fatty acid methyl esters) made by reacting natural vegetable or animal fats with methanol. Biodiesel fuel is becoming increasingly important and is expected to gain a large market share in the next several years. Regular diesel fuels blended with 2%, 5%, and 20% biodiesel are now commercially available. The large amount of glycerin generated from high volume usage of biodiesel fuel has resulted in this chemical becoming cost competitive with the glycols currently used in engine coolants. For this reason, and lower toxicity comparable to that of propylene glycol, glycerin deserves to be reconsidered as a base for antifreeze/coolant.

Coolant filters have been used for nearly 50 years by heavy duty engine manufacturers but little has been published in the technical literature documenting their performance. In heavy duty cooling systems an extender is periodically added to the system to prevent the coolant from becoming corrosive and replenish additives that stop the build-up of deposits which reduce heat transfer. Not only is the coolant filter the most convenient and reliable method to deliver the extender to the cooling system, it also removes debris from the coolant which can cause deposits and wear, aggravate corrosion, and even plug heat exchangers. Additionally, the used coolant filter serves as a diagnostic trouble shooting tool. This paper concentrates on the value or importance of filtering debris from the coolant of heavy duty diesel engine cooling systems. Published literature is reviewed and recent data from lab testing is reported.

A test method that will age coolants in a manner representative of coolant aging in the field is vital to the development of coolants that meet expected performance criteria. In an attempt to develop such a test, two approaches were taken. A phosphate buffered, molybdate/nitrite containing, propylene glycol based, heavy-duty coolant was aged in the laboratory using both a flow stand and a reflux apparatus. Samples of the coolant were taken at various time intervals during both tests. The samples were analyzed to determine glycol degradation product, sulfate and corrosion product accumulation, additive depletion, and pH changes. The results were compared to actual field results for the same coolant to determine which of the two approaches best simulated coolant degradation in the field. The flow stand appeared to best simulate actual field results.