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Chapter 6 COOLANT
Importance of LLC
Today's trend is smaller and lighter engines that can
offer greater output, lower fuel consumption and lower
exhaust emission levels.
Conditions to which engine coolant is subjected,
therefore, are becoming severer due to longer operat-
ing hours, higher coolant temperature and higher cool-
ant circulating speed.
Furthermore, many different materials such as steel,
aluminum, copper, solder and rubber are used in the
cooling system, and they are also subjected to the
severe conditions described above. Those materials
have different ionization characteristics, and this dif-
ference accelerates corrosion through the medium of
engine coolant. To prevent such a problem, it is nec-
essary to use the LLC having the additive that pre-
vents rust.
Characteristics of LLC
Additive and Points to
Remember
LLC contains several chemicals in such proportions
as to produce chemical reactions that suppress corro-
sion (ionization) of engine parts that contact with the
coolant. LLC loses its effectiveness by hours of use as
well as lapse of time.
Furthermore, if the chemicals are not well propor-
tioned to match the metals used in the cooling system,
certain chemicals in the LLC become rapidly used up
and result in dissolution of metals instead of protecting
metals from corrosion. Consequently, other corrosion
preventing chemicals react with dissolving metals and
accelerate corrosion. This condition generates more
severe corrosion than when plain soft water is used.
This is a typical problem caused by the use of inap-
propriate LLC.
6-8
Examples of Abnormali-
ties Caused by LLC
(Amine Type)
Pitting of Iron Parts
Amines are generally effective in suppressing the rust-
ing of ferrous metals, but they are said to become cor-
rosion promoter for copper parts.
Dissolved copper (copper corrosion) in the cooling
system deposits on iron parts and the copper deposits
cause corrosion and then pitting on iron parts that
have a high ionization characteristics due to galvanic
or local-cell action.
Corrosion of Aluminum Parts
Silicate is highly effective in protecting aluminum
against rusting. However, it is unstable in a solution in
which the pH is 9 or lower, and can turn to gel and pre-
cipitate in the solution. For this reason, the pH is usu-
ally specified to be about 10 to ensure a high alkaline
level.
This means, after silicate is used up, the high alkalinity
causes chemical attacks on aluminum. To prevent this
problem, proper maintenance of the coolant is
required. Examples: rapid wear of mechanical seals of
the water pump due to secondary effects of silicate gel
formation, corrosion of aluminum parts after silicate
used-up.
Pitting and Clogging of the Heat
Exchanger
When LLC deteriorates or when its concentration in
the coolant becomes low, the anti-corrosion perfor-
mance of LLC lowers and results in the corrosion of
metals. Brass and solder tend to corrode faster than
other metals, and corrosion of these metals is said to
cause water leakage and clogs. Example: Holes and
clogs in heat exchanger.
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