1. Antifreeze Formulations

LO 11-05: Describe and explain the classification, composition, and applications of various antifreeze formulations.

 

Antifreeze Formulations

The mixing of ethylene glycol or propylene glycol antifreeze and water alone is not an effective method to prevent the corrosion or erosion of cooling system components. In fact, the addition of antifreeze to water causes additional chemical reactions that require control. For example, ethylene glycol becomes acidic and corrosive when exposed to air; propylene glycol is also highly corrosive to a few metals. Foam suppressants, also called wetting agents , need to be added to maintain coolant contact with engine parts because steam and other vapor bubbles do not cool well. The development of antifreeze formulation is an evolutionary process driven by requirements to minimize corrosion and erosion in the cooling system, ensure material compatibilities, and minimize maintenance requirements. While the bases of most contemporary antifreezes are propylene glycol or ethylene glycol, the additive packages vary considerably, which can lead to confusion and severe maintenance problems if not properly understood and executed. It is the additive package that differentiates the various categories and classifications of antifreeze. TABLE 11-3 outlines the most common maintenance demands placed on antifreeze additive packages needed to produce a properly formulated coolant.

  TABLE 11-3: Cooling System Maintenance Concerns and the Additives Used for Prevention  
Condition Causes Effects Prevention
Scale Minerals present in water added to cooling system, particularly calcium and magnesium, that solidify and stick to hot metal surfaces Uneven metal expansion, scuffing, scoring, accelerated ring wear, and, depending on severity, cracked cylinder heads and/or blocks—the result of plugged cooling system passageways preventing heat transfer from cylinders Supplemental coolant additives to form a thin barrier on metal parts to prevent the adhesion of scale
Rust
  • Oxidized iron in cooling system
  • Damaged oxidation inhibitors caused by overheated coolant
 Plugged coolant passageways Supplemental coolant additive and diesel coolant additive with rust inhibitor
Acidity (low pH)
  • Chemical reaction between air and ethylene glycol antifreeze
  • Combustion gas leakage into the coolant
 Corrosion of iron, steel, and aluminum Supplemental coolant additive and diesel coolant additive with a pH buffer to maintain a slightly alkaline pH of the coolant
Cavitation Implosion of vapor bubbles against the cylinder walls
  • Perforation of cylinder walls
  • Leakage of combustion gases into the coolant, leaking coolant into the engine, or both
 Nitrite to act as a sacrificial barrier

 

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