Fuel, Oil and Coolant Specifications
among but not necessarily all the materials which make
Engine coolant is considered as any solution which is
up dissolved solids. Water, within the limits specified in
circulated through the engine to provide the means for
Tables 1 and 2 of Figure 1, is satisfactory as an engine
heat transfer from the various engine components. In
coolant when proper inhibitors are added.
general, water containing various materials in solution is
used for this purpose.
The function of the coolant is basic in the design and the
successful operation of the engine and must be carefully
A corrosion inhibitor is a water soluble chemical
selected and properly maintained.
compound which protects the metallic surfaces of the
cooling system against corrosive attack. Some of the
more commonly used corrosion inhibitors are
A suitable coolant solution must meet the following five
chromates, borates, nitrates, nitrites and soluble oil.
Depletion of all types of inhibitors occur through normal
1. Provide for adequate heat transfer.
operation and therefore strength levels must be
maintained by the addition of inhibitors at prescribed
2. Provide a corrosion resistant environment within the
intervals. Always follow the supplier's recommendations
on inhibitor usage and handling.
3. Prevent formation of scale or sludge deposits in the
Sodium chromate and potassium dichromate are two of
the best and more commonly used water system
4. Be compatible with the cooling system hose and
corrosion inhibitors. However, the restrictive use of
these materials, due to ecology considerations, has
deemphasized their use in favor of non-chromates.
5. Provide adequate freeze protection during cold
Care should be exercised in handling these materials
due to their toxic nature.
Normally requirements 1 through 4 are satisfied by
Chromate inhibitors must not be used in ethylene glycol
combining a suitable water with reliable inhibitors.
antifreeze solutions. Chromium hydroxide, commonly
When operating conditions dictate the need for freeze
called "green slime", can result from the use of
protection, a solution of suitable water and an ethylene
chromate inhibitors with permanent type antifreeze.
glycol type antifreeze containing adequate inhibitors will
This material deposits on the cooling system passages,
provide a satisfactory coolant.
reducing the heat transfer rate and will result in engine
overheating. Engines which have operated with a
chromate inhibited water must be chemically cleaned
Any water, whether of drinking quality or not, will
before the addition of ethylene glycol type antifreeze. A
produce a corrosive environment in the cooling system.
commercial heavy duty descaler should be used in
accordance with the manufacturer's recommendation for
Also, scale deposits may form on the internal surfaces
of the cooling system due to the mineral content of the
water. Therefore, water selected as a coolant must be
properly treated with inhibitors to control corrosion and
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
To determine if a particular water is suitable for use as a
adverse effects on heat transfer if the concentration
coolant when properly inhibited, the following
exceeds 1% by volume. For example: 1-1/4% of
characteristics must be considered. The concentration
soluble oil in the cooling system increases fire deck
temperatures 6% and a 2-1/2% concentration raises
dissolved solids. These materials are objectionable for
a number of reasons: chlorides and/or sulfates will
accelerate corrosion, while hardness (percentage of
magnesium and calcium present) will cause deposits of
scale. Total dissolved solids may cause scale deposits,
sludge deposits, corrosion or a combination of these.
Chlorides, sulfates, magnesium and calcium are