This is a great article on Cooling by Century Performance Center, Inc. COOLING SYSTEM BASICS Modern automotive internal combustion engines generate a tremendous amount of heat. This heat is created when the gasoline and air mixture is ignited in t he combustion chamber, and also from friction heat. This ignition (explosion) causes the piston to be forced down inside the engine, levering the connecting rods, and turning the crankshaft, creating power. Metal temperatures around the combustion chamber can exceed 1000° F. In order to prevent the overheating of the engine oil, cylinder walls, pistons, valves, and other components by these extreme temperatures, it is necessary to effectively dispose of the heat. It has been stated that a typical average-sized vehicle can generate enough heat to keep a 5-room house comfortably warm during zero degree weather (and I'm not talking about using the exhaust pipe). Approximately 1/3 of the heat in combustion is converted into power to drive the vehicle and it's accessories. It is our goal as racers to bring that 1/3 to a much higher standard, making use of every bit of energy to accelerate our vehicles. But, this higher standard also causes even greater heat generation, requiring even better cooling system components and designs to dissipate this additional energy by-product. Another 1/3 of the heat is carried off into the atmosphere through the exhaust system. The remaining 1/3 must be removed from the engine by the cooling system. Modern automotive engines have basically dumped the Air Cooled System for the more effective Liquid Cooled System to handle the job. In a liquid cooled system, heat is carried away by the use of a heat absorbing coolant (water and anti-freeze) that circulates through the engine, especially around the combustion chamber in the cylinder head area of the engine block. The coolant is pumped through the engine, then after absorbing the heat of combustion is circulated to the radiator where the heat is transferred to the atmosphere. The cooled liquid is then transferred back into the engine to repeat the process. (click image at right to enlarge) Excessive cooling system capacity can also be harmful, and may effect engine life and performance. You must understand that coolant temperatures also affect oil temperatures and more engine wear occurs when the engine oil is below 190° F. An effective cooling system controls the engine temperature within a specific range so that the engine stays within peak performance. In this system, the coolant is circulated by the water pump, and the thermostat controls the temperature. temperature. The thermostat is closed when the engine is cold, allowing coolant to circulate ONLY in the engine block, bypassing the thermostat and radiator. This allows the engine to warm up faster and uniformly so that "hot spots" are eliminated. When the warming coolant reaches the thermostat, the thermostat will begin to open and allow coolant to pass to the radiator. The hotter the coolant gets, the more the thermostat opens, allowing more volume of water to pass to the radiator. The thermostat also controls the length of time that the coolant remains in the radiator so that the heat is dissipated effectively. On a racing application you can get by without a thermostat by using the correct restrictor disc installed where the thermostat would normally be installed. Selecting the correct restrictor is imperative to system efficiency. Important Warning: Removing the thermostat to increase water flow because your vehicle is overheating is dangerous to your engine and is NOT what you want to do. Not only does the engine take longer to warm up, causing excessive metal-to-metal wear, but once the engine does warm up it can get too hot because the thermostat also controls the length of time that the water is in the radiator so as to dissipate the heat to the atmosphere.
THE PRESSURIZED SYSTEM Up until the late 1950's, liquid cooled systems did not operate under pressure. This was primarily because these cars had much larger radiators, more open air under the hoods allowing for more natural heat dissipation, and richer fuel mixtures causing lower (and less efficient) combustion temperature temperatures. s. With the manufacture of smaller vehicles, with smaller radiators, larger engines, and emission controls, along with the current use of unleaded fuels, more efficient cooling efficiency became necessary. The cure for this was to operate the cooling system under pressure, thus isolating it from atmospheric pressure. A system under pressure can handle higher temperatures, temperatures, and offers a higher static boiling point. NOTE: For every pound of pressure exerted on the coolant in the system, the static boiling point of the coolant is raised by approximately 3° F. Most liquids have a specific "boiling point", which is the temperature at which the liquid begins to change to a gas. If pressure is applied to the liquid, it must become hotter before it can boil. Pure water in a cooling system will boil (at sea level) at 212° F. At higher altitudes, atmospheric pressure is less than at sea level. Example: Water at 5,280 feet will boil at a mere 203° F. A cooling system that is under 15 pounds of pressure however, will now allow the water to reach nearly 250° F before it can boil. Even at this temperature the water is able to circulate through the engine, cooling parts that are at a much higher temperature without without the water boiling. As long as the coolant remains in liquid form it can do it's job and transfer heat to the radiator so it can be dissipated. Coolant that is boiling cannot transfer as much heat and engine overheating is likely to occur if the coolant turns to a gaseous state. Steam adjacent adjacent to a hot surface, such as a combustion wall, can actually act as an insulator - thus preventing any heat transfer to the coolant. Pressurization of the system is achieved by a special radiator filler neck and radiator pressure cap. The filler neck has an upper and lower sealing seat with an overflow tube connection between between them. The lower seat is engaged by the pressure controlling valve on the cap and the upper seat (in an open system) is engaged by a spring metal diaphragm in the cap. The radiator pressure cap features a spring pressure relief valve which closes off the lower sealing seat in the filler neck. This pressure relief valve allows pressure to build up to a specified level, the permits excess pressure to escape through the overflow tube when it exceeds the range of the pressure valve spring. This valve protects the cooling system from damage from excessive pressure. This pressure relief system also includes a vacuum relief valve that allows air (in an open system) to enter as coolant contracts. This prevents the radiator hoses and tanks from collapsing from the partial vacuum that would be created if air was unable to enter.
THE CLOSED or RESERVOIR SYSTEM vs. THE "OLD STYLE" OPEN SYSTEM One of the big disadvantages disadvantages in the old open type pressurized system is that as the system cools, air is allowed back through the overflow tube. These systems are not totally filled with coolant because of the potential for coolant loss through the overflow tube when the coolant heats up and expands. As more coolant is lost through the overflow, less coolant is left to do it's job within the engine. Because of this, and that air can enter the system and reduce cooling system efficiency, overheating can occur. Closed reservoir systems were first used by car manufacturers in the early 1970's.
A closed or reservoir system has solved the problems listed above. This system is different in that a special radiator cap and overflow reservoir tank. Part of the radiator cap is a second sealing gasket under the shell that contacts the upper sealing seat of the filler neck. What was the overflow hose is now the connection between the radiator and the "bottom" of the reservoir. While the open pressurized system is filled to a point 2-3 inches below the top of the radiator, the closed pressurized system is filled completely with coolant and the reservoir is f illed approximately half full. When the engine is started and begins to heat up, the coolant expands. expands. As the coolant expands it is forced out out through the pressure valve of the radiator cap, through the overflow tube, and into the reservoir. When the engine is turned off and begins to cool, a partial vacuum is created in the radiator by the contracting coolant. The upper sealing gasket in the pressure cap will then allow the vacuum to draw the coolant back into the radiator and engine from the reservoir. As you may have noticed, the actual volume of coolant that displaces during heat-up and cool-down transfer is minimal in most all cases. Because of the coolant going back and forth between the radiator and reservoir, practically all air is eliminated from the cooling system. This pretty much guarantees that the engine block, heater core, and radiator are full of coolant instead of air. This allows the most efficient operation of the cooling system. Generally, on closed systems, coolant is added only as required, and then it is added to the reservoir, not the radiator.
COOLANT and COOLANT ADDITIVES Even though some time ago water alone was used for many years in automotive cooling systems, the fact that it only has a 32 F° freezing point, a 212° F boiling point, it evaporates evaporates easily, creates rust and corrosion, and leaves mineral deposits has made it less than optimal as the sole coolant. It is much more efficient to utilize a chemical added the the water to improve the efficiency of the coolant. This chemical is commonly called "Anti-Freeze", "Anti-Freeze", but the more accurate name is ethylene glycol (EG). In recent years (EG) has been replaced by propylene glycol (PG). This is a much less dangerous chemical. PLEASE READ: Antifreeze is considered by many to be "one-size-fits-all" as most antifreeze brands have a distinctive lemon-lime color. However, However, the actual formulations can vary greatly between types, such as the more recent RED antifreeze. Conventional antifreeze is formulated from an ethylene glycol (EG) base chemical and can have very serious health risks. It is estimated that each year 90,000 pets and other wildlife die from accidentally ingesting ethylene glycol based antifreeze. Animals are attracted to antifreeze for its sweet smell and taste. Animals, and children for that matter, can accidentally ingest antifreeze from spills, cooling-syste cooling-system m leaks or improper improperly ly stored containers. Because of this the U.S. Government has initiated strict laws and penalties as the result of contamination of water or ground areas. Even a leaky vehicle can get you into trouble. As an alternative, automotive chemical manufacturers have formulated a newer type of antifreeze using propylene glycol glycol (PG) instead of ethylene glycol, which is less harmful if accidentally ingested. A popular brand is SIERRA®, which was the first nationally marketed propylene propylene glycol based antifreeze. Safer, propylene glycol based antifreeze provides performance and protection comparable to conventional ethylene glycol based antifreeze in four key areas of engine protection: protection: boil over, freeze-up, corrosion and heat transfer. SIERRA®, and other propyle propylene ne glycol based antifreeze products are available nationwide, and can be the extra margin of safety to protect your children, pets, drinking water, and neighborh neighborhood ood wildlife. Since antifreeze as a 50-50 mix with water elevates the boiling point to 227° F, and lowers the freezing point to -27° F, it should also be called anti-boil. Good quality antifreeze contains water pump lubricants to help maintain the efficiency of the pump, rust inhibitors to keep unwanted deposits from forming, and acid neutralizers to help protect the inside of the radiator, heater core, and hoses from corrosio corrosion. n. Of course, antifreeze does not last forever, so it is recommende recommended d that the coolant be changed at least every two years or 24,000 miles. However, many vehicle owners allow do not follow this service interval and allow
their cooling systems to become rusty, dirty, or clogged with mineral deposits. This causes water pump and hose failures, poor performance, overheating, and other component failures. To eliminate these problems it is best to have your vehicle's cooling system flushed in a professional shop that flushes and filters the coolant in your engine using equipment that is not only effective, but environmentally safe. The old way of simply using a flush kit with a water hose is illegal in many states and districts, and should not be attempted if you give a care about your family and the environment around you. Over time leaks can develop in the cooling system. If these leaks are not corrected you will lose excessive coolant which can cause overheating and engine damage. Although many leaks can be fixed as easily as tightening a hose clamp, in many cases you may still need to replace hoses, the water pump, various gaskets, or even radiator or heater core repair or replacement. Some chemical additives call "stop leaks" or "sealers" have been developed to stop some minor leaks from inside the cooling system. Most chemical sealers are derived from solutions which contain thousands of small particles that upon coming in contact with the leak will collect in sufficient quantity to where they clot up and stop the leak. These chemical sealers should only be used as a short term fix in certain circumstances, but can be quite effective. Just remember to only use them in moderation. Excessive use can cause other problems and they do not seal all leaks.
THE RADIATOR PRESSURE CAP The radiator pressure cap can be considered the safety valve of the cooling system. The pressure cap is comprised of: a top shell with two ears for engagement with the filler neck cams, a spring disc diaphragm (and upper sealing gasket) to seal against the top of the filler neck and to provide friction to hold the cap on the neck, a stainless steel pressure valve spring and pressure valve to seal against the bottom sealing seat of the filler neck, and, centered in the pressure valve is a vacuum relief valve (some are normally closed, while others are in a weighted-open position). The radiator filler neck's top sealing seat allows the cap's spring diaphragm to exert enough pressure to hold the cap on the neck. On the closed system, atmospheric pressure is sealed by the cap's upper gasket at this point. The lower sealing seat is where the pressure valve rests, permitting pressure to build as the coolant gets hotter. The filler neck cams are for the purpose of holding the cap in place, but also pressing the pressure valve onto the filler neck with exactly the right amount of preload. The filler neck cams also have a safety stop to prevent vibration from loosening the cap or causing a loss of system pressure. It also works as a limited safety from serious burns during cap removal on a hot or warm engine. This why you must "push and turn" to release the cap from its fully installed (closed) position.
The radiator cap should never be removed when the cap or radiator are hot to the touch. There is sufficient pressure in the system at this point that serious burn injury and scalding may occur. The radiator should be allowed to cool or be force-cooled by spraying water on the radiator core. Once the radiator has sufficiently cooled, take a rag or towel over the cap and turn it counter-clockwise 1/4 turn ONLY until it contacts the safety stop. Carefully observe for any coolant or steam loss around the rim of the cap and from the radiator overflow tube. Let that cap remain in this position until the pressure subsides. You can now press down on the cap and continue to turn it counter-clockwise and remove the cap. Always be sure that when you do this that the overflow cap should be removed or the overflow tube should be "open" so that steam has a place to exit. In a closed system the coolant coolant level can be routinely checked in the reservoir, and coolant can be added as needed. There are two types of vacuum relief valves made for radiator pressure caps. The Normally Closed (spring pressed) type, and the Normally Open (weighted) type. The normally closed cap design is what is called the constant pressure type cap. The vacuum is help in a closed position by a very light bronze spring. When the engine is started and begins to heat up, the system pressure starts to build up immediately because of the expansion of the coolant in the system. When the engine is stopped and begins to cool off, a partial vacuum tends to form in the system, which opens the vacuum valve to prevent the formation of excess vacuum in the system. The normally open type cap is what is called a pressure vent type cap. This vacuum valve hangs freely on the pressure valve and is equipped with a small calibrated weight. Under light operating conditions, conditions, the cooling system operates under no pressure (atmospheric). Should fast heating or overheating cause a quick expansion or boiling of the coolant, the escaping pressure pressure or steam activates the vacuum valve which will shut. The cap then operates the same as a constant pressure cap. When the engine is turned off and cools down, the vacuum valve again returns to the open position. The pressure type (Normally Closed) radiator cap is the preferred design used by most automakers. Cooling system engineers prefer to have cooling system operating at atmospheric pressure as much as possible to prevent constant strain on the radiator, hoses, and water pump seals.
THE THERMOSTAT The thermostat is the official sentry officer in the cooling system. It constantly monitors the temperature of the coolant and regulates the coolant flow through the radiator. Before the use of pressurized cooling systems, most thermostats were of the bellows type. They relied on a metallic bellows containing a few drops of volatile liquid (such as alcohol) which would expand at a certain temperature to open the thermostat valve. With the advent of of the pressurized cooling system, this bellows type thermostat became obsolete because the pressure in the cooling system prevented the bellows from opening at the correct temperature temperature.. Modern thermostats are powered by a temperature-sensitive, positive pressure, temperature-sensitive, heat motor. This is devised by using a specially formulated wax and powdered metal pellet tightly contained in a heatconducting copper cup that is equipped with a piston inside a rubber boot. Heat causes the wax pellet to expand, which forces the piston outward and then opens the valve. This heat motor senses temperature changes and will move the valve position to control coolant flow, thereby controlling coolant temperature temperature..
The thermostat is usually installed at the front of the engine on top of the engine block, though on some import vehicles it could be just about anywhere. The thermostat thermostat fits into a recess in the engine where it will be exposed to hot coolant. The top of the thermostat is covered by the water outlet housing that is used to connect the radiator hose to the radiator. There are two basic types of thermostats currently available: available: You have the balanced sleeve thermostat, and the reverse poppet thermostat. Both types function in the same manner, but have distinct differences. The reverse poppet thermostat opens against the flow of coolant from the water pump. The coolant, being under water pump pressure, is used to help the reverse poppet thermostat stay closed when it is cool so as to prevent leakage. The reverse reverse poppet thermostat thermostat valve is self-aligning and self-cleaning. The balanced sleeve thermostat allows pressurized coolant coolant to circulate around all of it's moving parts. For a performance engine application it is recommended to use the reverse poppet design for it's added flow capabilities. Important Warning: Removing the thermostat to increase water flow because your vehicle is overheating is dangerous to your engine and is NOT what you want to do. Not only does the engine take longer to warm up, causing excessive metal-to-metal wear, but once the engine does warm up it can get too hot because the thermostat also controls the length length of time that the water is in the radiator so as to dissipate the heat to the atmosphere. The thermostat permits proper warming of the engine from a cold startup. A slow warm up causes moisture condensation in the combustion chambers which can find it's way to the crankcase, causing sludge formation. The thermostat keeps the coolant temperatures above a specific minimum to provide proper engine combustion efficiency, extended engine life, and reduced combustion combustion emissions. It also prevents the metal around the combustion chamber "hot spots" from overheating because it allows coolant to circulate internally within the engine before it opens. Most engines are built with a coolant bypass for this purpose either as part of the engine assembly, or externally by a hose or other component. component. Engines that have external bypasses are usually disabled by the thermostat once the thermostat has opened to force all coolant through the radiator. The thermostat must begin to open at a specified temperature for the application, and when fully open must permit adequate coolant flow. Typically the thermostat begins to open 3° - 4° F above or below it's temperature rating (meaning a 180° thermostat will open between 176° F and 184° F.) and will be fully opened at about 20° F above it's initial opening temperature. The thermostat must meet standards that include allowing a sufficient coolant flow when fully open, and leak no more than a specified amount when fully closed. Most current thermostats feature either a bleed notch" or a "jiggle pin" that is designed to let trapped air in the system pass through the thermostat after refilling so as to eliminate hot spots during engine warm up. Since 1971, most domestic car manufacturers have used 192° F or 195° F thermostats as original equipment.. This permits the engine to operate at a higher temperature, equipment temperature, which allows the cooling system to operate at its best efficiency and to reduce engine emissions. On performance applications it is sometimes effective to go to a lower temperature rated thermostat so as to compensate for the added power output from the engine modifications. modifications. But, you must be very very careful when using lower thermostat thermostat ratings on computer-controlled computercontrolled engine applications. Because the computer relies on pre-programmed variables that are calculated by engine coolant temperatures as one of the variables, using a lower temperature thermostat thermostat without corresponding modifications to computer programming can cause problems.
THE WATER OUTLET The water outlet on the engine is the connection point between the engine and the upper radiator hose for which passes hot coolant to the radiator. The water outlet typically covers and seals the thermostat, and in some cases includes a thermostat bypass. Most water outlets are made from cast iron, cast aluminum, or stamped steel. If you decide to install a chrome water outlet, make sure you use one with a machined in groove for a sealing o-ring. Otherwise, the smooth chrome facing on the water outlet will not allow proper sealing and leaks will occur. It is actually better to utilize an aftermarket anodized anodized billet aluminum, or a cast iron version (when available). These offer the best overall overall sealing. If all you have is a stamped steel or cast aluminum, you will just have to make do with it and expect periodic leaks that will need to be repaired by gasket replacement and even sometimes replacing the water outlet itself.
Also note that cast iron and anodized billet aluminum are the best at resisting corrosion from the coolant and natural mineral deposits created in the cooling system. One of the most common leaks is over tightening, or uneven tightening of the water outlet mounting bolts. Being careful to correctly tighten the mounting bolts is the best way to prevent this.
THE RADIATOR The obvious function of the radiator is to lower the temperature of the coolant from the engine by transferring that heat to the atmosphere atmosphere.. The radiator is made of small tubes in "rows", called the "core" that are either positioned vertically (on older vehicles), or more the more common horizontal design (called a cross flow) that is in all newer vehicles. At the each end of the core is a "tank", one is the inlet tank and one the outlet tank. Factors that influence radiator efficiency include: the basic design of the radiator (core thickness, number of rows, tank capacity), the area and thickness of the radiator core that is exposed to cooling airflow, the amount of cooling air, and the difference between between the t emperature of the coolant and the temperature of the cooling air. Surprisingly, the greatest factor that will increase the radiator's efficiency is the difference between the Surprisingly, coolant and cooling air temperatures. This can only be done by raising the temperature of the coolant. Doing this permits the use of a smaller radiator (now you know of another reason that newer vehicles run at higher temperatures, temperature s, yet have smaller radiators than vehicles of the past). In a performance application we are constantly trying to find other ways to improve the radiator's efficiency to compensate for the added heat generated from the higher horsepower horsepower output. Installing a larger radiator, a radiator with more rows, larger tanks, higher fin count, or better design is where we usually end up. But, we can also improve the airflow efficiency by adding a fan shroud, electric fans, and higher output water pump. Aluminum radiators are the choice of most racers, and should your first choice if you must purchase a new radiator. One issue with radiator efficiency is on vehicles that have automatic transmissions. If this is you, and you have your OEM transmission lines still routed into your radiator for transmission fluid cooling, it is a very good idea to run a remote cooler for your transmission. Now, depending on your patience and vehicle knowledge, knowledg e, there are two issues you must understand. If you completely bypass the radiator and run your transmission fluid only in a separate cooler, it will take a bit longer for your transmission fluid to get to operating temperature. temperature. You will need to plug the unused transmission line connectors in your radiator. Air that gets in here will work against your cooling efficiency and can cause other problems. Just plug them and you should be OK.
HOSES and HOSE CLAMPS The upper and lower radiator hoses and heater hoses are all flexible connections between the engine, radiator, and heater core. Because of engine vibration, flexible connections are mandatory between between these areas. These hoses must be able to withstand the extreme heat environment under the hood of your vehicle as well as up to 20 pounds of internal pressure. Because of the wide temperature range of the coolant, they must also be compatible with below zero to over 250° F temperatures without fail. Air, coolant, and extreme temperatures all contribute to hose deterioration. Each one of these work against the life span of the hoses by causing the hoses to become hardened, cracked, softened, and swollen. All damage the hoses' flexibility and cause lining failure, rupturing, and clogging. Not only does this damage cause the hoses to fail, but rubber particles loosened from the hose linings can cause clogged radiators, heater cores, and thermostats. A weakened hose may collapse and cause restricted coolant flow and overheating.. You must periodical overheating periodically ly inspect all coolant hoses for deterioration and flush the cooling system at required intervals to prevent these problems.
Hose clamps are used on every coolant connector on an original engine from the manufacturer. Most of the time these clamps are "one use" versions made of sprung steel that do not like being loosened and retightened. I recommend that many of these OEM style clamps replaced if replacing or removing/ removing/installing installing coolant hoses. These OEM clamps can get bent or lose their concentricity that allows equal clamping force around the perimeter of the hose. These cheap spring metal clamps can also cut the hose when tightened. If this happens, leaks are likely to occur. For performance and racing applications it is recommended that AN (Army-Navy) (Army-Nav y) connections in conjunction with steel braided hoses be used. These fittings become an integral part of the hose and will thread into the braided hose's rubber liner. The connection at the compone components nts and engine is also threaded to another fitting. This type of connection is the most reliable and longest lasting, but it is also considerably more expensive.
THE WATER PUMP The water pump is obviously the heart of the cooling system. Just as your own heart pumps blood through your body, the water pump moves the coolant through your engine block's water passages. In an automotive engine, an impeller type water pump is used. There is typically a cast iron impeller plate that has fins, or a more typical stamped steel impeller attached to the pump shaft which forces the coolant out and away from the fins by centrifugal force as the impeller turns on the shaft. The impeller is enclosed in the water pump housing with a provision for coolant entry into the pump from the lower radiator hose connected to the radiator, and exits into the engine block and the rest of the cooling system. The modern OEM water pump is turned by either a V-belt or serpentine belt system on the front of the engine. Most water pump failures are caused by coolant leaking past the internal seal into the lubricated shaft bearings. This will be obvious by the presence of coolant leaking from one of the "weep" holes in the pump housing. The cause of this failure is either by the belt drive being too tight causing side-loading on the pump shaft, or by contaminants in the cooling system so that water pump components begin to rust and corrode. For performance and racing applications, a better choice (when available) is to install an electric water pump. These aftermarket units typically offer greater flow and more stable flow with less cavitation. Quality billet electric water pumps, like those from Meziere Billet Electric Water Pumps (one is shown above right) and others, offer light weight, precision performance for each application, and great looks with their anodized or polished finishes. Other benefits include: between round cooling (you do not need the engine running to circulate coolant. Therefore, the engine will get back to a cool temperature temperature between race rounds or hot laps); Increased horsepower because there is less mechanical power loss from a drive pulley and belt; and in many cases longer life because there is not a pulley and belt that is side-loading a shaft and bearing assembly. Of course, if you decide to run an electric water pump you need to have a compatible electrical charging system, system, and utilize electric radiator fans since you will no longer have a drive shaft mounting location for a mechanical fan.
THE MECHANICAL RADIATOR FAN and FAN CLUTCH The standard engine cooling (radiator fan) on many vehicles is of the mechanical type, meaning that it is belt-driven. In most cases the mechanical fan is mounted to the water pump snout and is driven off of the same pulley that rotates the water pump. The mechanical fan is very simple, and effective for most applications. The mechanical fans are typically made of stamped steel, but some aftermarket aftermarket fans can be fiberglass, or riveted stainless blades to a stamped steel center section. Blade count varies by application, some have 4, 5, 6 or 7 blades. Benefits of this type of fan is that it is cheap, it's simple, and it is always running. But, these can also be adverse affects. A fan that runs all the time takes power to make it work. Plus, this type of fan is not optimized at all engine speeds. Where some fans may work great a cruising speeds, they may be horrible at idle speeds (like stop and go traffic), or at higher engine speeds. Using an aftermarke aftermarkett fan increases airflow for better cooling, but at the expense of noise and at times even power. Some fans, like the riveted fans, can explode at certain upper RPMs and damage other engine and vehicle components. A better street performance performance and at many times street/strip fan is using a mechanical fan with a fan clutch. The fan clutch is designed to drive the engine fan when air movement is needed to cool the engine. A thermostatically controlled controlled fan clutch employs a bi-metal spring to adjust fan speed in response to operating temperature.. As engine temperature rises and the radiator heats up, the air passing the radiator into the fan temperature heats the spring coil and a silicone fluid in the clutch that enters the chamber increasing tension in the clutch and drives the fan. As coolant temperatures reduce, reduce, the fan clutch is allowed to slip, offering increased fuel efficiency and quieter operation. On the "non-thermal" fan clutch a silicone fluid with a very high shearing capability is used to drive the fan and cool the engine at lower engine speeds. As RPM increases the drive fluid allows the fan clutch to slip, increasing engine efficiency when less fan-assisted air movement is needed due to higher vehicle speeds. Because the fan clutch and water pump share a common shaft, if the fan clutch fails it usually takes out the water pump bearing with it. To tell if a fan clutch is failing, use these common symptoms:
The fan clutch locks up, thereby spinning at the same RPM as the water pump. This is obvious by increased fan noise and reduced fuel efficiency. You can test this by grabbing the fan with the engine OFF and trying to turn the fan. If there is excessive resistance, resistance, or you cannot spin the fan, the fan clutch should be replaced. The fan clutch will not engage and fails to turn the fan. The fan may still spin, but only as a result of centrifugal force from the already spinning pump. If you try to spin the fan with the engine OFF, the fan will spin freely with virtually no resistance. Replace the fan clutch. The fan clutch explodes. This is usually caused by severe bearing failure. Fan and fan clutch parts will contact and damage the hood and other under hood engine components (belts, hoses, battery, wiring, radiator, etc.) NOTE: This is almost always due to vehicle owner "laziness" in that one of the two items above had already occurred and were ignored or not periodically inspected.
Generally, fan clutch output under normal operating conditions will decrease by about 200 RPM per year. So, a three year old fan clutch is possibly due for replacement, or at least more periodic inspections. inspections. A four year old fan could very well be running partially disengaged and should be replaced.
THE ELECTRIC FAN Many new cars are taking advantage of electrical cooling fans because of their smaller engine compartments and greater airflow demands. It is well known that an engine can cool itself at cruising speeds of roughly 60 miles per hour in an average climate. But, with tighter under hood tolerances, unleaded fuels, higher combustion temperatures, temperatures, forward mounted catalytic converters, and other issues, a mechanical fan is not only impractical, but inefficient.
In the past, electrical cooling fans were "helper" fans for heavy towing and performance applications. applications. But now, many enthusiasts are dumping their mechanical fans in favor of the more efficient electric counterparts. Noise is reduced, horsepower is gained, mechanical water pumps last longer, and more efficient low speed cooling are all benefits of the electric fan. If you are exchanging a mechanical fan for an electric, be aware that proper shrouding and airflow requirements requireme nts are still a concern. You cannot just mount an electric fan and think it will solve all your problems.. Correct mounting location, fan shroud installation, the correct fan (or fans) to meet the airflow problems demand (calculated by engine horsepower, horsepower, vehicle weight, altitude and load) are all important if you want to do it right. Many aftermarket fans are rated by horsepower, and do not be surprised if in many cases you cannot find the fan that meets your power requirements. requirements. The only trick I can offer is to cover as much surface area of the radiator as possible, which may very likely mean multiple fans, and use a "puller" fan if it is your primary fan and a "pusher" if using it only as an auxiliary. Never use both a pusher and puller electric fan on the same radiator.
THE TRANSMISSION COOLER Over 90% of all transmission failures are caused by heat. The hotter the automatic transmission transmission fluid becomes, the more quickly it breaks down. Now, before you ask me why I included this in "cooling system tech", did you know that virtually all automatic transmission equipped vehicles vehicles run th e transmission fluid coolant lines to the radiator? These lines run parallel to the actual engine coolant lines in your radiator with inner "sub tanks" within your radiator's existing tanks. You can do yourself a great benefit by adding a separate transmission cooler to your automatic equipped vehicle. The minimum would be a 3/4" thick by 6" high by about 14" across. Though, you really should base your cooler demands by the weight, converter stall, and load applied to the vehicle. A mild street car can go with the minimum, but if you have a lock-up trans, a high stall converter, a camper or trailer, or other added load capacity or race environment, a much larger transmission fluid cooler should be installed. You may bypass the radiator as the transmission fluid cooler, but make very sure you are using an independent independe nt cooler that meets your specific requirements for the vehicle it is installed on.
