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.
Coolant Filter Elements
Replaceable elements are available with various chemical inhibitor systems. Compatibility of the element with
other ingredients of the coolant solution cannot always be taken for granted. Problems have developed from
the use of the magnesium lower support plate used by some manufacturer's in their coolant filters. The
magnesium plate will be attacked by solutions which will not be 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 critical. The use of an aluminum or zinc support plate in preference to magnesium is recommended to
eliminate the potential of this type of deposit.
High-chloride coolants will have a detrimental effect on the water softening capabilities of systems using ion-
exchange resins. Accumulations of calcium and magnesium ions removed from the coolant and held captive
by the zeolite resin can be released into the coolant by a regenerative process caused by high chloride content
Bulk Inhibitor Additives
Commercially packaged inhibitor systems are available which can be added directly to the engine coolant or to
bulk storage tanks containing coolant solution. Both chromate and nonchromate systems are available and
care should be taken regarding inhibitor compatibility with other coolant constituents.
Nonchromate inhibitor systems are recommended for use in Detroit Diesel engines. These systems can be
used with either water or permanent-type antifreeze solutions and provide corrosion protection, pH control and
water softening. Some nonchromate inhibitor systems offer the additional advantage of a simple on-site test to
determine protection level and, since they are added directly to the coolant, require no additional hardware or
When freeze protection is required, a permanent-type antifreeze must be used. An inhibitor system is included
in this type of antifreeze and no additional inhibitors are required on initial fill if a minimum antifreeze
concentration of 30% by volume is used. Solutions of less than 30% concentration do not provide sufficient
corrosion protection. Concentrations over 67% adversely affect freeze protection and heat transfer rates (Fig.
Methoxy propanol base antifreeze is NOT RECOMMENDED for use in Detroit Diesel engines due to the
presence of fluoroelastomer (Viton) seals in the cooling system. Before installing ethylene glycol base
antifreeze in an engine previously operated with methoxy propanol, the entire cooling system should be
drained, flushed with clean water, and examined for rust, scale, contaminants, etc. If deposits are present, the
cooling system must be chemically cleaned with a commercial grade heavy-duty descaler.
Ethylene glycol base antifreeze is recommended for use in Detroit Diesel engines. Methyl alcohol antifreeze is
NOT recommended because of its effect on the nonmetallic components of the cooling system and because of
its low boiling point.
The inhibitors in permanent-type antifreeze should be replenished at approximately 500 hour or 20,000 mile
intervals with a nonchromate inhibitor system. Commercially available inhibitor systems (Fig. 2) may be used
to reinhibit antifreeze solutions.