Coolant Selection-Additives - Dodge ram truck 3500 1996 Service Manual

7 - 10 COOLING SYSTEM
D E S C R I P T I O N A N D O P E R A T I O N {Continued)
prevents freezing down to -67.7 deg. C (-90 deg. F). A
higher percentage will freeze at a warmer tempera­
ture. Also, a higher percentage of antifreeze, can
cause the engine to overheat because the specific
heat of antifreeze is lower than that of water.
111 Percent Ethylene-Glycol—Should Not Be Used in
Chrysler Vehicles
Use of 100 percent ethylene-glycol will cause for­
mation of additive deposits in the system, as the cor­
rosion 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 deg. C (300) deg. F). This temperature is hot
enough to melt plastic and soften solder.. The
increased temperature can result In engine detona­
tion. In addition, 100 percent ethylene-glycol freezes
at 22 deg. C (-8 deg. F ).
Propylene-glycol Formulations—Should lot le Used in
Chrysler Vehicles
Propylene-glycol formulations do not meet
Chrysler coolant specifications. It's overall effec­
tive temperature range is smaller than that of ethyl­
ene-glycol. The freeze point of 50/50 propylene-glycol
and water is -32 deg. C (-26 deg. F). 5 deg. C higher
than ethylene-glycol's freeze point. The boiling point
(protection against summer boil-over) of propylene-
glycol is 125 deg. C (257 deg. F ) at 96.5 kPa (14 psi),
compared to 128 deg. C (263 deg. F) for ethylene-gly­
col. Use of propylene-glycol can result in boil-over or
freeze-up in Chrysler vehicles, which are designed for
ethylene-glycol. Propylene glycol also has poorer heat
transfer characteristics than ethylene glycol. This
can increase cylinder head temperatures under cer­
tain conditions.
Propylene-glycol/Ethylene-glycol Mixtures—Should Not Be
Used in Chrysler Vehicles
Propylene-glycol/ethylene-glycol Mixtures can
cause the destabilization of various corrosion inhibi­
tors, causing damage to the various cooling system
components. Also, once ethylene-glycol and propy­
lene-glycol based coolants are mixed in the vehicle,
conventional methods of determining freeze point will
not be accurate. Both the refractive index and spe­
cific gravity differ between ethylene glycol and propy­
lene glycol.
CAUTION: Richer antifreeze mixtures cannot be
measured with normal field equipment and can
cause problems associated with 100 percent ethyl­
ene-glycol.
COOLANT SELECTION-ADDITIVES
The presence of aluminum components in the cool­
ing system requires strict corrosion protection. Main­
tain coolant at specified level with a mixture of
ethylene glycol based antifreeze and water. Only use
an antifreeze containing ALUGARD 340-2 ® such as
Mopar Antifreeze. I f coolant becomes contaminated
or looses color, drain and flush cooling system and fill
with correctly mixed solution.
CAUTION: Do not use coolant additives that are
claimed to improve engine cooling.
RADIATOR PRESSURE CAP
Radiators are equipped with a pressure cap, which
releases pressure at some point within a range of
97-124 kPa (14-18 psi). The pressure relief point (in
pounds) is engraved on top of cap.
The cooling system will operate at pressures
slightly above atmospheric pressure. This results in a
higher coolant boiling point allowing increased radi­
ator cooling capacity. The cap (Fig. 21) contains a
spring-loaded pressure relief valve that opens when
system pressure reaches release range of 97-124 kPa
(14-18 psi).
Fig. 21 Radiator Pressure Cap and Filler Neck-
Typical
A vent valve in the center of cap allows a small
coolant flow through cap when coolant is below boil­
ing temperature. The valve is completely closed when
boiling point is reached. As the coolant cools, i t con­
tracts and creates a vacuum in the cooling system.
This causes the vacuum valve to open and coolant in
the reserve/overflow tank to be drawn through its
connecting hose into radiator. I f the vacuum valve is
stuck shut, the radiator hoses will collapse on cool-
down. Clean the vent valve (Fig. 21).
A rubber gasket seals radiator filler neck to pre­
vent leakage. This is done to keep system under
pressure. I t also maintains vacuum during coolant
cool-down allowing coolant to return from reserve/
overflow tank.