Fuel, Oil and Coolant Specifications
de-scaler should be used in accordance with the
manufacturer's recommendation for this purpose.
Soluble Oil
Soluble oil has been used as a corrosion inhibitor for
many years. It has, however, required very close
attention relative to the concentration level due to
adverse effects on heat transfer if the concentration
exceeds 1% by volume. For example: 1-1/4% of
soluble oil in the cooling system increases fire deck
temperatures 6% and a 2-1/2% concentration raises
fire deck temperature up to 15%. Soluble oil is not
recommended as a corrosion inhibitor.
Non- Chromates
Non-chromate inhibitors (borates, nitrates, nitrites,
Fig. 2 - Heat Transfer Capacity
etc.) provide corrosion protection in the cooling system
with the basic advantage that they can be used with
compound which protects the metallic surfaces of the
either water or a water and permanent type antifreeze
cooling system against corrosive attack. Some of the
solution.
more commonly used corrosion inhibitors are chro-
mates, borates, nitrates, nitrites and soluble oil.
Depletion of all types of inhibitors occur through
INHIBITOR SYSTEMS
normal operation. Therefore, strength levels must be
maintained by the addition of inhibitors at prescribed
intervals. Always follow the supplier's recommenda-
An inhibitor system (Fig. 3) is a combination of
tions on inhibitor usage and handling.
chemical compounds which provide corrosion protec-
tion, pH control and water softening ability. Corrosion
NOTE: Methoxy propanol base permanent
protection has been discussed under the heading
antifreeze (such as Dowtherm 209, or equiva-
C o r r o s i o n Inhibitors. The pH control is used to
lent) must be re-inhibited only with compatible
maintain an acid free solution. The water softening
corrosion inhibitor systems.
ability deters formation of mineral deposits. Inhibitor
systems are available in various forms such as coolant
filter elements, liquid and dry bulk inhibitor additives,
and as an integral part of permanent antifreeze.
Chromates
Sodium chromate and potassium dichromate are two
of the best and most commonly used wafer system
Coolant Filter Elements
corrosion inhibitors. However, the restrictive use of
these materials, due to ecology considerations, has de-
Replaceable elements a r e available with various
emphasized their use in favor of non-chromates. Care
c h e m i c a l inhibitor systems. Compatibility of the
should be exercised in handling these materials due to
element with other ingredients of the coolant solution
their toxic nature.
cannot always be taken for granted.
Chromate inhibitors should not be used in permanent
Problems have developed from the use of the
magnesium l o w e r s u p p o r t p l a t e u s e d b y s o m e
t y p e antifreeze solutions. Chromium hydroxide,
manufacturer's in their coolant filters. The magnesium
commonly called "green slime", can result from the
u s e of chromate inhibitors with permanent type
plate will be attacked by solutions which will not be
antifreeze. This material deposits on the cooling
detrimental to other metals in the cooling system. The
system passages, r e d u c i n g the heat transfer rate
dissolved magnesium will be deposited in the hottest
zones of the engine where heat transfer is most
(Fig. 2), and results in engine overheating. Engines
which have operated with a chromate-inhibited water
critical. The use of an aluminum or zinc support plate
i n preference to magnesium is recommended to
must be chemically cleaned before the addition of
eliminate the potential of this type of deposit.
permanent type antifreeze. A commercial heavy duty
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