Importance of Coolant To Long Engine Life
At one of the seminar sessions conducted by the education committee of the IAFC preceding the annual conference at Seattle, a brief discussion brought to light some of the problems and frustrations experienced by some fire chiefs in obtaining the planned service life from their apparatus. That preventive maintenance plays an important part in achieving the planned service life was clearly indicated.
A planned, active, service life of 20 years is not unreasonable for fire apparatus, considering the limited chassis and engine mileage for this period as compared to commercial vehicle use and mileage. (The Rating Bureau standard is 15 years). Actually, modern fire apparatus is capable, given proper maintenance, of providing a reliable service life of 30 years.
However, as brought out in the seminar discussion, in many instances fire departments have been unable to achieve even the 15-year service life because of the inability to get replacement parts. This has compelled a premature retirement or sale of the apparatus, or in some departments, the apparatus is held to cannibalize for parts to keep other apparatus in service. Of the examples given, one will suffice to illustrate the need for better maintenance practice for the cooling system which could have prevented the loss of the engine and use of the apparatus for several months.
Pinholes in block: A cylinder block in an engine approximately nine years old developed pinholes in the cylinder walls. A new cylinder block was not available. A “short” block had to be purchased to salvage the apparatus. This is an engine assembly less accessories: fan, inlet and exhaust manifold, fuel pump, carburetor, air cleaner, alternator, governor etc. The cost, when installed, was equal to the resale value of the apparatus. This type of situation, regrettably, is getting to be quite common. Manufacturers, to reduce service inventories, are stocking units or assemblies for service replacement rather than individual parts. There is also a trend to further limit the time period that such units or assemblies are available. This emphasizes the need for a better understanding of and closer attention to maintenance requirements.
The best maintenance, alone, will not prevent some part failures, and some replacements must be made because of normal wear.
In the case cited a better understanding of cooling system requirements could have prevented the pinholes that caused the loss of an engine, but the fire department never received the full details and the reason for closer attention. For the thousands of fire departments that need this information, a detailed explanation follows.
What coolant should do: The basic requirements for a coolant in a cooling system for any internal combustion engine are to:
- Provide an adequate medium for transfer of heat from the combustion area and surrounding the cylinders to the atmosphere,
- Prevent corrosion in the cooling system,
- Prevent the formation of scale or sludge,
- Control the pH condition,
- Be compatible with all metals in the system, hose and sealing materials,
- Provide adequate protection against freezing when required by climatic conditions.
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The efficiency of the cooling system for the modern engine must be sustained continuously if proper engine operation and anticipated service life are to be realized. During the last 30 years, the engine power output per cubic inch of displacement has nearly doubled (0.216 bhp/cu.in. dis. to 0.419 bhp/cu. in dis.) with only a moderate increase to cooling system size, about 10 percent.
Water is not enough: Water has long been the basic fluid used in engine cooling systems, but water only as a coolant will no longer satisfy cooling system requirements. Water must be combined with a suitable inhibitor to control and prevent corrosion, prevent foaming, preserve a pH balance to neutralize acids or excessive alkalinity, dissolve scale and provide a lubricant for water pump seals.
Water, unless distilled, carries dissolved solids, such as chlorides, sulfates, magnesium, calcium, iron and other contaminates, causing corrosion, scale deposits, sludge formation or a combination of these troubles.
Water also acts as an electrolyte in the electrochemical destruction of metals in the cooling system. It was electrolysis that caused the pinholes in the cylinders mentioned above. Electrolytic action is also the cause of pinholes in radiator tubes. There will be more on electrochemical activity in the cooling system in this column next month.
Test specifications: Water to be used in the engine cooling system should test within the limits shown in the following table:
If the values given above are exceeded, the water should be distilled, or demineralized, or deionized before using. If only the hardness value is exceeded, the water should be treated with a softener before use.
Information on how the water in your area tests can usually be provided by the water board chemist or the board of health.
In any event, an inhibitor in the coolant is a must for year-round use.
First, follow the recommendations of the engine manufacturer for the selection and use of an inhibitor.
Problems increasing: If no specific recommendation is given in the manual, and none has been given in the most manuals (except for diesel engines), an inhibitor, either alone or as part of a filter-inhibitor-cathode system, should be a definite requirement on a maintenance schedule. The problems of corrosion and electrochemical activity have been getting more acute and credit must go to the diesel engine manufacturers for doing something about it! They are providing—as standard—a filter-inhibitor cathodic protection system.
An inhibitor is a chemical compound available as a chemically active element. Two types of inhibitor (a) chromate formula or (b) all-purpose year-round (borate) are available for fire service use. For engines not equipped with a filter-inhibitor-cathodic protection unit, the inhibitor Nalcool 2000 is recommended by engine manufacturers as providing a complete cooling system treatment in ready-to-use form. A system treatment, after flush-cleaning the system, is one pint of Nalcool 2000 for each four gallons of system capacity. This inhibitor is compatible with all brands of permanent-type antifreeze (ethylene glycol). It is a product of Nalco Chemical Company, 6216 West 66th Place, Chicago, Ill. 60638.
The additives that make the inhibitor so effective in controlling corrosion, preventing and removing scale, and providing other beneficial actions, are slowly consumed in the process of providing this essential protection. Renewal of the inhibitor to replace the lost additives is essential with any system, and should be done every six months.
Semi-annual replacement: With Nalcool 2000, the replacement rate is one pint every six months. Every two years, the system should be drained and flushed and a new coolant solution used. If back-flushing is done, scale and rust particles are loosened that may not all drain out. After back-flushing, flush the system in the normal manner with the radiator outlet-water pump inlet hose removed to be sure all rust and scale particles are removed.
Where operation of the apparatus requires protection from freezing, a permanent type of antifreeze (ethylene glycol) should be used. The antifreeze should test 30 percent, which protects to 0°F. The engine and antifreeze manufacturers recommend a 50 percent concentration for the inhibitor properties which the antifreeze also provides. Antifreeze should be changed every year, as time and service cause deterioration of the antifreeze.
A new type of permanent antifreeze has been widely advertised during this past year. All engine manufacturers warn against the use of this anti-leak antifreeze. In the fire service, with intermittent operation, stuck thermostats and valves in vent caps are two of the possible troubles. Do not use it!
This discussion of cooling system maintenance will be continued in next month’s column. Technical data is through the courtesy of the Detroit Diesel Engine Division, General Motors Corporation.