Fuel, Oil and Coolant Specifications
DETROIT DIESEL
more commonly used corrosion inhibitors are chro-
mates, borates, nitrates, nitrites and soluble oil.
Depletion of all types of inhibitors occurs through
normal operation. Therefore, strength levels must be
maintained by the addition of inhibitors at prescribed
intervals. Always follow the supplier s recommenda-
tions on inhibitor usage and handling.
Chromates
Sodium chromate and potassium dichromate are two
of the best and `most commonly used water system
corrosion inhibitors. However, the restrictive use of
these materials, due to ecology considerations, has de-
emphasized their use in favor of non-chromates. Care
should be exercised in handling these materials due to
their toxic nature.
Fig. 2 - Heat Transfer Capacity
Chromate inhibitors should not be used in permanent
type antifreeze solutions. Chromium hydroxide,
chemical compounds which provide corrosion protec-
commonly called "green slime", can result from the
tion, pH control and water softening ability. Corrosion
use of chromate inhibitors with permanent type
protection is discussed under the heading Corrosion
antifreeze. This material deposits on the cooling
Inhibitors. The pH control is used to maintain an acid-
system passages, reducing the heat transfer rate
free solution. The water softening ability deters
(Fig. 2) and results in engine overheating. Engines
formation of mineral deposits. Inhibitor systems are
which have operated with a chromate-inhibited water
available in various forms such as coolant filter
must be chemically cleaned before the addition of
elements, liquid and dry bulk inhibitor additives, and
permanent antifreeze. A commercial heavy-duty de-
as an integral part of permanent antifreeze.
scaler should be used in accordance with the
manufacturer s recommendation for this purpose.
Coolant Filter Elements
Soluble Oil
Replaceable elements are available with various
Soluble oil has been used as a corrosion inhibitor for
chemical inhibitor systems. Compatibility of the
many years. It has, however, required very close
element with other ingredients of the coolant solution
attention relative to the concentration level due to
cannot always be taken for granted.
adverse effects on heat transfer if the concentration
exceeds 1% by volume. For example: 1 1/4% of soluble
Problems have developed from the use of the
o i l in the cooling system increases fire deck
magnesium lower support plate used by some
temperature 6% and a 2 1/2% concentration raises fire
manufacturers in their coolant filters. The magnesium
deck temperature up to 15%. Soluble oil is not
plate will be attacked by solutions which will not be
recommended as a corrosion inhibitor.
detrimental to other metals in the cooling system. The
dissolved magnesium will be deposited in the hottest
zones of the engine where heat transfer is most
Non-chromates
critical. The use of an aluminum or zinc support plate
in preference to magnesium is recommended to
Non-chromate inhibitors (borates, nitrates, nitrites,
eliminate the potential of this type of deposit. High
etc.) provide corrosion protection in the cooling system
chloride coolants will have a detrimental effect on the
with the basic advantage that they `can be used with
water softening capabilities of systems using ion-
either water or a water and permanent antifreeze
exchange resins. Accumulations of calcium and
solution.
magnesium ions removed from the coolant and held
captive by the zeolite resin can be released into the
INHIBITOR SYSTEMS
coolant by a regenerative process caused by high
chloride content solutions.
An inhibitor system (Fig. 3) is a combination of
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