6-8
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.
Many different materials such as steel, aluminum,
copper, solder and rubber are used in the cooling sys-
tem, and they are also subjected to the severe condi-
tions described above. Those materials have different
ionization characteristics, and this difference acceler-
ates corrosion through the medium of engine coolant.
To prevent such a problem, it is necessary to use the
LLC having the additive that prevents 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 in contact with the
coolant. LLC loses its effectiveness by hours of use as
well as lapse of time.
Moreover, if the chemicals are not well proportioned 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.
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. For case example, rapid wear of mechanical
seals in the water pump due to secondary effects of
silicate gel formed. Corrosion of aluminum parts after
silicate is consumed.
Pitting and Clogging of Radia-
tor
When LLC deteriorates or when its concentration in
the coolant is too low, the anti-corrosion performance
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
radiator.
