Chapter 6
COOLANT
6-7
Importance of LLC
Today's trend is toward smaller and lighter engines
offering 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 characteris-
tics, and this difference accelerates corrosion through
the medium of engine coolant.
To prevent such a problem, the use of LLC (long life
coolant) is very important.
Characteristics of LLC
additive and important
notes
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 inappropriate LLC.
Examples of abnormali-
ties caused by LLC
Pitting of iron parts
Amines are generally effective in suppressing the rust-
ing of ferrous metals, but they are said to cause prob-
lems 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 the radi-
ator
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
