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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.

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.