Agricultural Mechanics PDF 8206-A Operation & Service of Engine Cooling Systems

# AGRICULTURAL MECHANICS 8206-A ## OPERATION AND SERVICE OF ENGINE COOLING SYSTEMS ### INTRODUCTION When the fuel/air mixture burns inside an internal combustion engine, the temperature of the burning vapors can instantly reach $3,600$ to $4,000^\circ F$. Approximately one third of the heat energy...

# AGRICULTURAL MECHANICS 8206-A ## OPERATION AND SERVICE OF ENGINE COOLING SYSTEMS ### INTRODUCTION When the fuel/air mixture burns inside an internal combustion engine, the temperature of the burning vapors can instantly reach $3,600$ to $4,000^\circ F$. Approximately one third of the heat energy is converted to usable power. Another third is passed out of the engine through the exhaust system. The remaining third must be removed by a cooling system. Therefore, the purpose of the cooling system is to 1) prevent engine overheating, and 2) regulate engine temperature at a proper operating level. To prevent engine overheating and parts from literally melting together, two types of cooling systems are used on modern engines. * Air-cooled systems use air circulating around the outside of the engine block and head to dissipate the heat. Air cooled systems are used mainly on small, light to medium duty single or multi-cylinder gasoline engines, and on a few diesel engines. These engines normally do not operate under severe hot conditions. * Liquid-cooled systems use a liquid coolant circulating through internal engine cavities and passages to carry away the excess heat. When engineers design an engine, they consider the amount of heat that is produced in the combustion chamber under normal conditions. They also consider the distance certain parts will expand and contract as the engine operates. By taking these and other factors into consideration, they scientifically and mathematically determine the tolerances or space between moving parts. They must also determine the needed capacity of the cooling system. Operating the engine at the correct temperature is just as important as preventing the engine from overheating. Operating an engine at a temperature cooler than which it was designed will cause unnecessary wear, poor fuel economy, and an accumulation of condensation and sludge in the crankcase. On the other hand, operating the engine at a temperature hotter than which it was designed, but not totally overheating it, will also cause unnecessary wear. In addition, pre-ignition, detonation of fuel, burned values, scored pistons, and general lubrication failure will occur. An example of pre-ignition is ignition of the fuel/air mixture resulting from a piece of extremely hot carbon inside the combustion chamber because the engine is operating at a temperature that is too high. Detonation occurs when the fuel/air mixture burns too rapidly and can result in vibration in the cylinder walls. ### OPERATION AND SERVICE OF AN AIR-COOLED SYSTEM | Component | Description | |---|---| | Cylinder Wall | 3600 Deg. F | | Cooling Fins | | | Combustion Chamber | | | Head Baffle | | | Cylinder Baffle | | | Air Flow Deflector | | | Blower Shroud | | | Engine Body | | Air-cooled engines have many thin metal cooling fins molded on the block and head assemblies to increase the surface area for air contact. Shrouds and sheet metal are placed around the engine to direct the flow of air from the fan across these fins. Heat moves from a hotter area to a cooler area. The excess heat will travel to the tips of the fins as long as they are being cooled by the cooler air blast. ### OPERATION OF A LIQUID-COOLED SYSTEM | Component | Description | |---|---| | Engine Water Jacket | | | Coolant | | | Overflow Tube | | | Thermostat | | | Fan | | | Pressure Cap | | | Sending Unit | | | Bypass | | | Fan Drive Belt | | | Coolant Filter | | | Water Pump | | | Hose | | | Radiator | | | Overflow Reservoir | | | Air | | | Shroud | | The water pump is the heart of a liquid cooling system. It pumps up to 125 gallons per minute of coolant from the top of the engine block and head to the radiator. A temperature regulated valve called a thermostat is placed between the engine block and the radiator. The thermostat may contain a fluid filled bellows or a bimetallic spring that expands and contacts at different temperatures. When the engine is cold or is first started, the thermostat remains closed. Part of the coolant is circulated through a bypass tube back to the engine block and head. The engine will quickly reach operating temperatures. As the engine warms, the temperature controlled thermostat opens allowing heated coolant to circulate to the top of the radiator. Since one function of the cooling system is to maintain proper operating temperatures, the thermostat is constantly opening and closing to regulate the coolant flow. The radiator is made of many small tubes with thin fins attached to increase the surface area. As the hot coolant is pumped through the radiator, the heat is transferred to the metal tubes or core, to the thin metal fins, and finally to the cooler air as it passes over the fins. A large fan enclosed in a shroud is used to concentrate the air blast and direct it through the radiator fins. As the hot coolant flows from the top to the bottom of the radiator, it is cooled by the forced air flow. The vacuum created by the water pump pulls the cooled coolant from the bottom of the radiator and recirculates it through the water jacket in the engine block and head. Flexible hoses are used to connect the different component parts and isolate the radiator from harmful vibrations from the engine. ### WATER Water is the universal coolant used in liquid cooling systems. It is plentiful, cheap, and absorbs heat readily. Water as a coolant by itself, however, can cause additional problems if appropriate steps are not taken. Water will 1) freeze at temperatures below $32^\circ F$; 2) evaporate rapidly at high temperatures at which engines normally operate; and 3) can cause internal metal parts to corrode. Water with high mineral levels such as calcium or iron, will 4) also cause mineral deposits or scale to form. It will form inside of the water jacket or radiator on hot metal surfaces. The speed of heat transfer through approximately $1/16$ inch layer of rust and scale is equivalent to the speed of heat transfer through $4 1/2$ inches of cast iron. It is easy to see that rust and scale will reduce the efficiency of the cooling system and quickly cause overheating problems. Even cleaned, filtered, and treated water from city or rural water distribution systems often contains high dissolved mineral levels. For this reason, it is recommended that clean rain water, or distilled water be added to cooling systems. ### USES OF ANTIFREEZES AND ADDITIVES An antifreeze solution can be added to prevent the coolant from freezing at temperatures below $32^\circ F$. Other chemical additives are also added to the antifreeze to help inhibit scale, rust and corrosion, and to control foam and acid formation. The correct amount of antifreeze to use is determined by the capacity of the system and the lowest anticipated temperatures for the geographic area. This temperature is based on a 50 year average from the U.S. Weather Bureau. This information is normally provided in the operator's manual and/or on the antifreeze container. For example: An engine with a coolant system capacity of 12 quarts operating in the Texas Panhandle would need at least 6 quarts of antifreeze. This solution would provide protection to $-34^\circ F$. The U.S. Weather Bureau Map indicates temperatures of between $20^\circ F$ and $25^\circ F$ have been recorded over the last 50 years. The strength of the antifreeze solution can be checked by using a special hydrometer to check the specific gravity. The number of small balls or the height an indicator floats in the antifreeze solution will indicate the concentration of antifreeze. ### FREEZING PROTECTION TABLE FULL STRENGTH "PERMANENT" ANTIFREEZE REQUIRED | Cooling System Capacity in Quarts | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12| |---|---|---|---|---|---|---|---|---|---|---|---|---| | 9 | $24^\circ$ | $14^\circ$ | $0^\circ$ | $-21^\circ$ | $-50^\circ$ | | | | | | | | | 10| $25^\circ$ | $16^\circ$ | $4^\circ$ | $-12^\circ$ | $-34^\circ$ | $-62^\circ$ | | | | | | | | 11 | $26^\circ$ | $18^\circ$ | $8^\circ$ | $-6^\circ$ | $-23^\circ$ | $-47^\circ$ | | | | | | | | 12 | $20^\circ$ | $19^\circ$ | $10^\circ$ | $-4^\circ$ | $-15^\circ$ | $-34^\circ$ | $-57^\circ$ | | | | | | | 13 | $21^\circ$ | $13^\circ$ | $3^\circ$ | $-9^\circ$ | $-25^\circ$ | $-45^\circ$ | $-66^\circ$ | | | | | | | 14| $22^\circ$ | $15^\circ$ | $6^\circ$ | $-5^\circ$ | $-20^\circ$ | $-38^\circ$ | $-59^\circ$ | | | | | | | 15 | $22^\circ$ | $16^\circ$ | $8^\circ$ | $0^\circ$ | $-18^\circ$ | $-34^\circ$ | $-54^\circ$ | | | | | | | 16 | $23^\circ$ | $17^\circ$ | $10^\circ$ | $2^\circ$ | $-12^\circ$ | $-26^\circ$ | $-43^\circ$ | $-62^\circ$ | | | | | | 17 | $24^\circ$ | $18^\circ$ | $12^\circ$ | $5^\circ$ | $-8^\circ$ | $-19^\circ$ | $-34^\circ$ | $-52^\circ$ | | | | | | 18 | $25^\circ$ | $19^\circ$ | $14^\circ$ | $7^\circ$ | $0^\circ$ | $-10^\circ$ | $-21^\circ$ | $-34^\circ$ | $-50^\circ$ | $-65^\circ$ | | | | 19 | $26^\circ$ | $20^\circ$ | $15^\circ$ | $9^\circ$ | $2^\circ$ | $-7^\circ$ | $-16^\circ$ | $-28^\circ$ | $-42^\circ$ | $-56^\circ$ | | | | 20 | $27^\circ$ | $20^\circ$ | $16^\circ$ | $10^\circ$ | $4^\circ$ | $-3^\circ$ | $-12^\circ$ | $-22^\circ$ | $-34^\circ$ | $-48^\circ$ | $-62^\circ$ | | | 21 | $28^\circ$ | $21^\circ$ | $17^\circ$ | $12^\circ$ | $6^\circ$ | $0^\circ$ | $-9^\circ$ | $-17^\circ$ | $-28^\circ$ | $-41^\circ$ | $-54^\circ$ | | | 22 | $29^\circ$ | $22^\circ$ | $18^\circ$ | $13^\circ$ | $8^\circ$ | $2^\circ$ | $-6^\circ$ | $-14^\circ$ | $-23^\circ$ | $-34^\circ$ | $-47^\circ$ | | | 23 | $30^\circ$ | $23^\circ$ | $19^\circ$ | $14^\circ$ | $9^\circ$ | $4^\circ$ | $-3^\circ$ | $-10^\circ$ | $-19^\circ$ | $-29^\circ$ | $-40^\circ$ | | | 24 | $31^\circ$ | $24^\circ$ | $20^\circ$ | $15^\circ$ | $10^\circ$ | $5^\circ$ | $0^\circ$ | $-8^\circ$ | $-15^\circ$ | $-24^\circ$ | $-34^\circ$ | | Two types of antifreezes are used. * Alcohol-based antifreeze is cheaper, but has a boiling point lower than water. It is not recommended in engines that operate above $180^\circ F$ because it will boil away. * Ethylene-Glycol based antifreeze has a boiling point higher than water ($230^\circ F$) and has been nicknamed "permanent antifreeze." This name has become very misleading. The term permanent antifreeze means only that the solution will not boil away at normal engine temperatures. It does not mean that it can be left in the engine permanently. The system should be flushed and coolant replaced once a year. Even though the "anti-freezing" protection of permanent antifreeze may not have boiled away, the other chemical additives for anti-corrosion, rust, foaming, etc. are no longer effective. When temperatures do not drop below freezing or in the summer, it is tempting to use only water as a coolant. This is not a recommended practice because the system is not protected against rust and corrosion. Separate anti-corrosive additives, etc. can be purchased and added to water for summer use. However, modern antifreeze solutions are now formulated to be used as both a winter antifreeze and a summer coolant. They contain all the necessary additives for normal engine operation and protection, and can be left in the system for one year. A solution of at least 25 to 33 percent antifreeze is recommended as a summer coolant to provide adequate corrosion and rust protection. ### PRESSURE TYPE RADIATOR CAP Most large gasoline and diesel engines are designed to operate most efficiently at between $170^\circ F$ and $220^\circ F$. However, water will begin to evaporate rapidly at around $180^\circ F$ and will boil at $212^\circ F$. To prevent the coolant from evaporating and boiling, the system is allowed to pressurize by using a spring loaded pressure cap. The boiling point of the coolant is raised approximately $3^\circ F$ for each one pound of pressure in the system. By using a cap that will hold up to 15 psi of pressure, the boiling point of the coolant inside the system can be raised to approximately $260^\circ F$. The engine can then operate at it's most efficient temperature without the coolant boiling away. The pressure cap is actually two valves in one. When the engine heats above normal operating temperatures and pressures, the coolant expands and begins to boil. A pressure valve will open and release excess pressure through an overflow tube at the top of the radiator neck. As the engine cools, the coolant will contract and a vacuum is created inside the coolant system. A vent or vacuum valve will then open and allow air to be drawn back into the system to prevent the radiator tubes or hoses from collapsing. However, this repeated action can cause the coolant level to decrease over time even at normal operating temperatures. This is especially true if the spring in the cap is a little weak; the rubber gasket is not properly sealing; or a lower pressure rating cap has been installed. As the engine heats and the coolant expands, water and antifreeze vapor may be blown out through the overflow tube. As the coolant cools, air is drawn back into the system through the vent valve. Since oxygen is necessary for rust and corrosion formation, this can accelerate the buildup inside the coolant system. New designs help overcome this problem and maintain the proper coolant level. The overflow tube from the radiator neck is submerged in a separate container. As the engine heats, pressure and coolant are released through the pressure cap and overflow into an overflow reservoir. When the engine cools and a vacuum is created, coolant instead of air is drawn back into the radiator. ### SERVICE AND MAINTENANCE OF THE COOLING SYSTEM The operator's manual of the particular vehicle or engine should be consulted when performing service procedures. It may contain instructions that apply only to the specific brand, model, or style of vehicle or engine you are servicing. A word of caution must be expressed! An engine can be operating at a normal temperature of $220^\circ F$ with a pressurized cap installed and the coolant will not be boiling. The instant the pressure is released, the coolant will start to boil and steam will be released. Always allow the engine and coolant to cool before removing the radiator cap. Most radiator caps have two stops. The first safety stop allows the cap to only partially open. This permits any pressure to escape out the overflow pipe before the cap is completely removed. To prevent serious burns, always take extra precautions. Follow recommended procedures outlined in the operator's manual for the specific engine you are operating. Use heavy gloves and cover the radiator cap with rags when removing it. As a general rule, the coolant level should be checked daily. It is recommended that the cooling system be drained and flushed annually and new antifreeze added. #### CAUTION! Properly store both old and new antifreeze in properly marked closed containers away from children. Because antifreeze is poisonous, it should be handled and disposed of properly. Antifreeze has a sweet taste and a pleasant smell. This making it inviting for small children, pets, and livestock to drink if left in open containers. Recycling and disposal centers are now set up in most communities to help insure a safe environment. Radiators can become plugged both internally and externally. Scale, and mineral deposits will form on the inside of the tubes. Sludge will settle to the bottom of the tank and reduce water flow. Commercial flushing/cleaning compounds are available to loosen and dissolve scale and sludge so they may be flushed out. #### ANOTHER WORD OF CAUTION! The flushing and cleaning compounds are caustic and can cause skin irritation or burns. Also, some cleaners are not recommended for use in systems with aluminum parts. Always follow operator's manual and label directions for specific procedures for the type and model equipment or vehicle you are servicing. Properly neutralize and dispose of all chemicals. In some cases, the radiator may have to be removed and taken to a radiator repair shop. The repair person can "boil" the radiator in a stronger chemical solution to remove mineral scale and sludge. In severe cases, the top and bottom tanks of the radiator must be removed and the core physically rodded to remove mineral deposits. Air flow through the air inlet screens and radiator fins is reduced by cotton lint, leaves, chaff, oil and dirt mixture, and other trash. These conditions will decrease the efficiency of the cooling system and cause the engine to overheat. High pressure air, high pressure washers, and steam cleaners can be used to blow or wash the screens and radiator core as needed. Screens and radiator cores should be cleaned in the reverse direction of the air flow of the fan. Be careful not to bend the thin radiator fins as they will also reduce air flow. The fan belts and pulleys should be inspected regularly. Belts with cracks, glazed edges, torn covers, or broken cords should be replaced. Worn or loss belts will slip in the pulleys and reduce fan and water pump speed. This will decrease the efficiency of the cooling system and lead to serious engine damage. Excessive belt tension can cause premature belt wear and reduce the life of the bearings in the water pump, alternator and/or fan belt idler. Check the operator's manual for the correct belt deflection and procedures for adjustment. A fair rule of thumb is one-half to one inch deflection between pulleys with approximately 25 psi of force. Always check the fan for bent blades or cracks. Cracked or missing fan shrouds can create a potentially dangerous situation for the operator as well as reduce the air flow through the radiator core. Radiator hoses and connections, should be regularly checked for deterioration and leaks. Some types of hoses will become hard, brittle, and crack with age. Others will become very soft and swollen allowing the inner lining to peel lose. Most lower radiator hoses have a spiral wire or coil inside to prevent them from collapsing from the suction created by the water pump and restrict coolant flow. If a hose bursts, all coolant is suddenly lost and the engine can immediately overheat. Always replace hoses with the correct size and type as recommended by the engine manufacturer. The cooling system may be checked for both internal and external leaks. Fill the radiator to the proper level. This is usually one-half to two inches below the radiator neck. A pressure tester is attached to the top neck of the radiator. Slowly build up pressure in the system with the hand pump until the normal operating level of the radiator cap is reached. Do not over pressurize the system. A hose could burst, a gasket blow out, or a radiator tube could rupture. After the system is pressurized, watch the gauge to see if the pressure holds steady. If it falls, check for external leaks at all joints, connections, and gaskets. If no leak is found, start the engine and heat the engine to normal operating temperature. A leak may not show up until certain parts have heated and expanded to their operating condition. A tell-tell sign of a leak or seep is paint discoloration. If the pressure continues to decrease and no external leaks are found, internal leaks can be suspected. Internal leaks are harder to detect. Signs of internal coolant leaks include 1) milky white oil after the engine has been ran for a short time, or 2) coolant and/or water dripping from the engine oil drain plug when the drain plug has been loosened until only the last thread is holding. The radiator cap may also be tested with the radiator tester with a special adapter. A used pressure cap should hold pressure to within approximately one and one-half psi of the manufacturers' specification. Thermostats can be tested if they are suspected of sticking open or closed. Place the thermostat and a thermometer in a container of water that can be heated. They should be suspended so they will not touch the sides or bottom of the container. Stir the water as the temperature rises. The thermostat should begin to open at the temperature stamped on its body (plus or minus a few degrees). It should be fully open at approximately $20^\circ F$ above rated temperature. The thermostat should close as it is removed from the heated water. The thermostat may however, only stick intermittently. Because of their low cost, many engine manufacturers now recommend that thermostats be replaced annually as part of the regular preventive maintenance program. Always install a thermostat with the temperature range recommended by the engine manufacturer. Most modern engines use forced flow water pumps so coolant is always circulating. The pump shaft bearings are factory sealed and lubricated, and require little or no maintenanceHowever, it is a good practice to periodically shake the pump shaft to see if any slack can be detected. This may indicate that the bearing and shaft needs to be replaced. A ceramic seal separates the inner water pump impeller from the external bearing housing and hub. If the seal begins to fail or the bearing and shaft become worn, coolant will leak externally through a small opening or "weep hole." The water pump should be removed and the bearing and seal replaced immediately if coolant is leaking. Specific instructions are included in water pump kits, and/or provided in the appropriate engine technical manual. Several other conditions can cause serious problems inside a modern liquid cooling system. Galvanic or electrolytic corrosion is caused by a static electrical current set up between two or more unlike metals. This is similar to the corrosion on the different metals inside a common flashlight. Because a combination of aluminum, brass, cast iron, steel, and other metal alloys are now used in the engines and cooling system, precautions must be taken. Most major brands of antifreeze and summer coolants now contain additives to help control these damaging effects. Chemicals help prevent the flow of electricity through the coolant. Additional additives help to neutralize the corrosive salts that are created. Cavitation erosion is an eroding action caused by repeated collapsing or bursting of tiny vapor bubbles on the coolant side of the cylinder wall or sleeve. It is believed to be caused by higher operating temperatures and vibration of the cylinder walls or sleeves of certain high performance engine designs. Many modern diesel and gasoline engines are equipped with thin "wet sleeves." This allows the cylinder walls (sleeves) to be replaced separately when they become worn. It also allows the coolant to be closer to the actual combustion chamber to remove excess heat faster. The wet sleeves are installed into the engine block with a press fit and are clamped by the cylinder head. They are sealed above and below the water jacket by o-rings. On the power stroke, extreme pressures can cause minute vibrations to set up in the sleeves even though they are clamped firmly. Steam vapor bubbles are created in the vacuum area between the coolant and the outside sleeve surface area. As these vapor bubbles collapse and burst, they do so with great force. This repeated action can pit the outside of the sleeve wall. Although the bubbles are a lot smaller in size, this action is similar to how water and steam bubbles would dance across a hot skillet. This action can literally erode holes completely through the cylinder wall or sleeve if uncontrolled. This allows coolant to enter the combustion chamber and drain into the oil pan. Research has shown that cavitation erosion can be controlled by maintaining the proper pH level in the coolant, and by conditioning the metal sleeves with a slick protective surface. Additives are now available to add to the coolant if cavitation is recognized as a potential problem area by the engine manufacturer. Because of varying engine designs, cavitation erosion is not a problem in all engines. Follow recommendations listed in the operator's manual for exact procedures and precautions. ### COOLANT FILTERS AND CONDITIONERS Coolant filters and conditioner canisters have become a common part of the liquid coolant system on many large engines. As the coolant circulates through the engine block, it also circulates through a large filter. The filter helps remove any rust, scale, dirt, or grit particles that may be circulating in the coolant. Many filters also contain a slow release capsule of different chemicals and additive conditioners. As the coolant circulates, the chemicals and additives are slowly dissolved. Some chemicals form a protective film on the surface of the cylinder sleeves or walls. This film acts as a barrier against the collapsing of the vapor bubbles from cavitation erosion as discussed earlier. Other chemicals in the slow release capsule help to replace those additives in the antifreeze that "wear out" before new antifreeze is replaced annually. ### TEMPERATURE SENSING FAN CLUTCHES Many modern engines are now equipped with temperature sensing fan drive clutches. These clutches are attached between the fan drive and the fan. They serve two purposes. First, they regulate coolant temperature by controlling the amount of air that is forced through the radiator. They also help to conserve engine horsepower. A typical 18 inch automotive engine fan can consume over two engine horsepower when rotating at 3,000 RPM. Larger truck and tractor fans will consume much more. When air flow through the radiator is not needed to cool the engine coolant, the fan clutch will automatically reduce the speed of the fan and save energy. Fan drive clutches are fluid couplers containing silicone oil or gel. A bimetallic coil or strip on the coupler senses temperature and opens and closes a value to regulate the amount of silicone oil circulating. Other couplers are filled with silicone gel that changes viscosity (resistance to flow) with changing temperatures. The more silicone flowing through the coupler, the faster the fan will turn and the more air supplied for cooling. **Acknowledgements** Dr. Joe Muller, Curriculum Specialist, Instructional Materials Service, developed and organized the information in this topic. Mr. Rodney Schmalride, Graduate Assistant, Department of Agricultural Education, Texas A&M University, developed the student activities. **References:** Cavitation Erosion, Case I-H, Racine, WI. Fundamentals of Machine Operation: Preventive Maintenance, Deere and Company, Moline IL. Fundamentals of Service: Engines, Deere and Company, Moline IL. Fundamentals of Service: Fuels, Lubricants and Coolants, Deere and Company, Moline IL. Tractor Maintenance, American Association for Vocational Instructional Materials, Athens, GA.