The purpose of the coolant (antifreeze or water) flowing through your diesel is to regulate the heat within the cylinder head and engine block that's created by the combustion process. In order to accomplish that job the coolant must be pumped around the engine compartment, pick up heat from the engine, transfer that heat into the radiator, all while limiting corrosion, lubricating the water pump, and not freezing.
Traditional antifreeze is a mixture that is 50 percent mix of ethylene glycol (EG) and 50 percent water. There are also propylene-glycol-based (PG) products on the market, and they have some different but interesting performance characteristics when compared to EG.
If the proper coolant isn't used, corrosion, overheating, or water-pump failure could occur in your diesel engine.
Both ethylene glycol and propylene glycol fall into the glycols family that is much larger than the two formulations mentioned. Glycol is used in various forms not only as antifreeze but also in resin formulations, plastics, solvents, fertilizer, food products, shaving cream, chemical production, and as an airplane deicer.
In most instances the ethylene glycol and propylene glycol base are not produced by the company that is selling the antifreeze; it's purchased from manufacturers such as the Dow Chemical Corporation. When ethylene glycol is used as a coolant, the exact formulation of additives is what defines the difference in brands.