Grand Cherokee 4WD Laredo V8-4.7L (2002)
Coolant: Description and Operation
Engine Coolant
DESCRIPTION - ENGINE COOLANT
EETHYLENE-GLYCOL MIXTURES
CAUTION: Richer antifreeze mixtures cannot be measured with normal field equipment and can cause problems associated with 100 percent
ethylene-glycol.
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 degrees C (-35 degrees F). The antifreeze concentration must always
be a minimum of 44 percent, year-round in all climates. If percentage is lower than 44 percent, 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 percent antifreeze
concentration, which prevents freezing down to -67.7 degrees C (-90 degrees 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.
Use of 100 percent ethylene-glycol will cause formation of additive deposits in the system, as the corrosion inhibitive additives in ethylene-glycol
require the presence of water to dissolve. The deposits act as insulation, causing temperatures to rise to as high as 149 degrees C (300) degrees F).
This temperature is hot enough to melt plastic and soften solder. The increased temperature can result in engine detonation. In addition, 100 percent
ethylene-glycol freezes at 22 degrees C (-8 degrees F).
PROPYLENE-GLYCOL MIXTURES
Its overall effective temperature range is smaller than that of ethylene-glycol. The freeze point of 50/50 propylene-glycol and water is -32 degrees C
(-26 degrees F). 5 degrees C higher than ethylene-glycol's freeze point. The boiling point (protection against summer boil over) of propylene-glycol
is 125 degrees C (257 degrees F) at 96.5 kPa (14 psi), compared to 128 degrees C (263 degrees F) for ethylene-glycol. Use of propylene-glycol can
result in boil-over or freeze-up on a cooling system designed for ethylene-glycol. Propylene glycol also has poorer heat transfer characteristics than
ethylene glycol. This can increase cylinder head temperatures under certain conditions.
Propylene-glycol/ethylene-glycol Mixtures can cause the destabilization of various corrosion inhibitors, causing damage to the various cooling system
components. Also, once ethylene-glycol and propylene-glycol based coolants are mixed in the vehicle, conventional methods of determining freeze
point will not be accurate. Both the refractive index and specific gravity differ between ethylene glycol and propylene glycol.
OPERATION
Coolant flows through the engine block absorbing the heat from the engine, then flows to the radiator where the cooling fins in the radiator transfers
the heat from the coolant to the atmosphere. During cold weather the ethylene-glycol coolant prevents water present in the cooling system from
freezing within temperatures indicated by mixture ratio of coolant to water.
