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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.

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.

An overview of extended service interval (ESI) and long life coolant (LLC) and how these topics are related to engine type and duty cycle, to coolant chemistry, and to coolant maintenance practices is presented. For purposes of this paper, ESI is defined as a minimum of 100K miles between routine additions of supplemental coolant additive (SCA). A brief description of Fleetguard ESI/LLC products is given. Finally, a brief status report of work being done to develop industry standards for ESI/LLC products is presented.

A test strip containing three pads for measuring the freezepoint protection, molybdate and nitrite levels in heavy-duty diesel engine cooling systems has been developed for commercial use. The test strip requires no pretreatment or dilution of the sample, other than to allow it to cool to 130 degrees F or lower, and gives results for all three tests within two minutes. The test results are sufficiently accurate, and the strips are stable over extended periods of time, provided the container is kept tightly closed and away from direct sunlight and prolonged elevated temperatures when not in use. The freezepoint test offers an inexpensive alternative to refractometers. Since it can be used with either ethylene or propylene glycol coolants, it is recommended over the use of hydrometers.

Coolant containing the proper amount of glycol and additives is critical to the reliability and durability of heavy duty diesel engines. Occasional coolant analysis is required in the field to insure that the proper coolant composition is maintained, otherwise severe engine damage can occur. There are several types of coolant test kits currently available in the field as well as commercial coolant analysis services. Some of the test methods used provide information that does not predict or correlate with a coolant's capability to prevent system corrosion and deposit formation. This paper examines the more widely available field coolant analysis methods and documents their strengths and weaknesses. Further, recommendations are made as to acceptable laboratory methods for the analysis of engine coolants.

Cavitation corrosion of cylinder liners in heavy duty engines can be one of the significant limits in engine operating time between overhauls. In both laboratory and engine dynamometer studies, engine coolants based on propylene glycol (PG) have performed better than similar formulations based on ethylene glycol with regard to cast iron cavitation corrosion. The performance of PG base coolant in all other aspects of coolant use was equivalent or superior to both industry standards and existing ethylene glycol (EG) products designed for use in heavy duty engines. Additionally, propylene glycol is cost competitive, readily available, and less toxic compared to ethylene glycol. A propylene glycol base engine coolant is described which assists the heavy duty user in solving many current problems related to cooling system servicing and engine life.

Cast aluminum alloys 356 and 319 and wrought alloy 3003 were corrosion tested in a commercial (Fleetguard DCA-4) supplemental coolant additive (SCA) package modified by varying the potassium nitrate level. Electrochemical techniques were used to determine the stability of the passive film as a function of nitrate concentration. Cyclic potentiodynamic polarization and cyclic galvanostaircase polarization were the principle techniques used and compared. In the presence of the other inhibitors, the passive film stability did not change as the nitrate concentration varied. The corrosion resistance of each alloy was more dependent on the alloy chemistry with 3003 being the most resistant and 319 being the least. The two electrochemical techniques provided results consistent with each other.