MAINTENANCE
FEATURE
Understanding
failures in
cooling system
By Oliver Biyogo
C
Mr Biyogo is the Lubricants
technical services manager at
Total Kenya Limited
ooling system failures is one
of the most common causes of
engine breakdown.
It contributes more than 22%
of automotive engine failures. Some of these
breakdowns can be through;
corrosion,
•
cavitation in the water pump, cylinder
head and liners
• Deposits that can cause blockage and
abrasive wear
• Damage of the water pump impeller
due to coolant starvation resulting in
overheating
• Incompatibility with seals which leads
to seal porosity and hardening which
manifests itself in form of cracks that
eventually cause leakages
• Overheating that can have detrimental
effects
• Component failure due to coolant
freezing(for winter environments)
Cooling system failures contribution to
engine breakdown is not easily discernible
because it effects manifests themselves
22
indirectly. It calls for a thorough root cause
analysis techniques by the maintenance
personnel.
A coolant formulation requirement
should:
Allow for Heat Transfer, provide boiling
or freezing protection, and provide material
protection of the components. This
functionality is provided by a combination
of 45%-70% Demineralised water, 25%-50%
Glycol (MEG-Mono-ethylene Glycol or MPGMono-propylene Glycol) and 3%-8% additives
respectively.
Traditionally, pure water was used for cooling
purposes because of its ability to ‘’carry’’ heat.
This property is defined in physics as the heat
or thermal capacity. Water posses’ excellent
specific heat capacity. Other liquid substances
with high heat capacity include ammonia (Used
as a refrigerant), hydrogen etc.
However, water has its drawbacks. It boils at
100 degrees and freezes at Zero degrees. This can
pose a serious problem depending on a vehicle
operating environment. Also, components
exposed to plain water are susceptible to rusting
and corroding. No wonder radiator repair is big
business in Kenya.
In some applications i.e. rail locomotives,
ability to dissipate heat has a higher precedence
than boiling or freezing protection. Glycol
in itself as compared to water, exhibits lower
thermal conductivity-ability to transfer heat
(between 0.2-03 compared to 0.6 for water).In
essence the technical reasoning against glycol
for rail application, is it will form a ‘’thermal
insulating layer’’ around the components thus
jeopardising its ability to transfer heat and
subsequent overheating problems. It is not
strange for such application to use plain water
and dosing it with a corrosion inhibitor in the
cooling system.
In automotive application both on-road and
off-road, no OEM recommends use of water.
Coolant technology is mainly classified
either as mineral based or organic based. The
technology could function either through
formation of a protective layer on the metal
surface or through oxidation which is a
chemical reaction resulting in oxide formation
on the metal surface. The choice of technology
is dependent on technological constraints (i.e
high temperature engines, material evolution of
the components, and volume reduction of the
engine) and environmental constraints
Mineral inhibitor technology coolants are
cheaper but exhibit high additive depletion,
poor thermal and oxidation stability, loss of heat
September 2015 • | Lubezine Magazine