Coolant

The required ethylene-glycol (antifreeze) and water mixture depends upon the climate and vehicle operating conditions. The recommended mixture of 50/50 ethylene-glycol and water will provide protection against freezing to -37° C (-35° F). The antifreeze concentration must always be a minimum of 44%, year round, in all climates. If percentage is lower than 44%, engine parts may be eroded by cavitation, and cooling system components may be severely damaged by corrosion. Maximum protection against freezing is provided with a 68% antifreeze concentration, which prevents freezing down to -67.7° C (-90° F). A higher percentage will freeze at a warmer temperature. Also, a higher percentage of antifreeze can cause the engine to overheat because the specific heat of antifreeze is lower than that of water.

100 Percent Ethylene-Glycol Should Not Be Used
Use of 100 Percent Ethylene-Glycol will cause formation of additive deposits in the system, as the corrosive inhibitive additives in ethylene-glycol require the presence of water to dissolve. The deposits act as insulation, causing temperatures to rise as high as 149° C (300° F). this temperature is hot enough to melt plastic and soften solder. The increased temperature can result in engine detonation. In addition, 100 % ethylene-glycol freezes at 22° C (-8° F).

Propylene-Glycol Formulations Should Not Be Used
Propylene-glycol formulations do not meet the required specifications. It's overall effective temperature range is smaller than that of ethylene-glycol. The freeze point of 50/50 propylene-glycol and water is -32° C (-26° F), 5 degrees higher than ethylene-glycol's freeze point. The boiling point (protection against summer boil-over) of propylene-glycol is 125° C (257° F) at 96.5 kPa (14 PSI), compared to 128° C (263° F) for ethylene-glycol. Use of propylene-glycol can result in boil-over and freeze up. Propylene-Glycol also has a poorer heat transfer characteristics than ethylene-glycol. This can increase cylinder head temperatures under certain conditions.

Propylene-Glycol/Ethylene-Glycol Mixtures Should Not Be Used
Propylene-glycol/ethylene-glycol mixtures can cause the destabilization of various corrosion inhibitors, causing damage to the coling system components. Also, once ethylene-glycol and propylene-glycol based coolants are mixed in the vehicle, conventional methods of determining the freeze point will not be accurate. Both the refractive index and specific gravity differ between the ethylene-glycol and propylene-glycol.

CAUTION: Richer antifreeze mixtures cannot be measured with normal field equipment and can cause problems associated with 100 percent ethylene-glycol.