Understanding High Performance Radiators

A radiator is a heat exchanger that lowers the temperature of the liquid coolant after it leaves the internal combustion engine. Radiators are made from header and collector tanks linked by a core with many narrow passages that provide a high surface area relative to volume. A radiator cools the coolant that has absorbed the heat energy from the engine. A radiator does not return the temperature of the coolant back to ambient air temperature, but it is enough of a transfer to keep the engine from overheating.

Up until the 1980s, radiator cores were primarily made from copper (for fins) and brass (for tubes, headers, tanks, and side plates). Starting in the 1970s, the use of aluminum increased due to its reduced weight and cost. Eventually, aluminum took over the vast majority of vehicular radiator applications. Modern radiator cores are usually made of stacked layers of metal sheeting that has been pressed to form channels. The channels are soldered or brazed together.

 

 

The header tank of the radiator is located either on the top of the radiator or along one side. Hot coolant is fed into the header tank, distributed through the radiator core through tubes, and passes to the collector tank on the opposite end of the radiator. As the coolant passes through the radiator tubes, it transfers much of its heat to the tubes, which transfers the heat to the cooling fins that are between each row of tubes. The cooling fins release the heat to the ambient air. Cooling fins are used to increase the contact surface of the tubes to the air, thus increasing heat transfer efficiency. The cooled coolant is fed back to the engine, and the cycle repeats.

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This Tech Tip is From the Full Book, HIGH PERFORMANCE AUTOMOTIVE COOLING SYSTEMS. For a comprehensive guide on this entire subject you can visit this link:

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Since air has a lower heat capacity and density than liquid coolants, a fairly large volume flow rate must be moved through the radiator core to absorb the heat from the coolant. Radiators often have one or more fans that blow or pull air through the radiator. To save fan power consumption, radiators are often behind the front grille. This position aids in cooling because a fan in front of the radiator would impede airflow. Ram air can give a portion or all of the necessary cooling airflow when the coolant temperature remains below the system’s designed maximum temperature and the fan remains disengaged.

 

 

Thermosiphon Cooling Systems

Early motor vehicles used thermosiphon circulation to move cooling water between the cylinder block and the radiator. This system depended on forward movement of the car and fans to move enough air through the radiator to provide the temperature differential that caused the thermosiphon circulation. As engine power increased, an increase in flow was required, so engine-driven pumps were added to assist circulation.

More compact engines used smaller radiators and required more convoluted flow patterns, so the circulation became entirely dependent on the pump. It might even be reversed against the natural circulation.

An engine cooled only by thermosiphon is susceptible to overheating during prolonged periods of idling or very slow travel. In these instances, airflow through the radiator is limited unless one or more fans are able to move enough air to provide adequate cooling. These systems are also very sensitive to low coolant levels because losing even a small amount of coolant stops the circulation.

 

 

 

 

 

Radiator Design

A properly designed cooling system consists of the right size radiator, a water pump with a good flow rate, and a cooling fan (either mechanical or electric) that provides enough airflow at idle or low RPM. At highway speeds, the air flowing through your radiator will keep your engine at operating temperature. The radiator is located between the cooling fan and the vehicle header panel.

The radiator removes heat from the coolant by conduction and convection, which is explained in detail in chapter 1. Conduction is the transfer of heat from molecule to molecule through solids and fluids that are in contact. Convection is heat transfer by the molecular motion in the heated substance itself and only takes place in liquids and gases. It is heat that is transferred to the cylinder wall from combustion, goes into coolant, and is carried away to the radiator.

 

Radiator Core

Heated coolant circulates in the radiator core, where coolant flows through coolant tubes. The tubes are exposed to the air flowing through the core, which has metal cooling fins between the tubes. Heat is transferred through the coolant tube walls along with the soldered joint to the cooling fins. These cooling fins are usually oval shaped to create turbulence in their airways, which helps transfer the heat between the core metal surfaces and the air flowing through the radiator. The air that flows through the radiator removes heat from the coolant and carries it away.

Coolant tubes are created from 0.0045 to 0.012 inch (0.1 to 0.3 mm) sheet brass or aluminum, using the thinnest possible materials for each application. This material is rolled into round tubes and the joints are sealed with a locking seam.

 

 

Cellular or Film Design Core

Early radiators, such as those used in a Model T, were shaped like a honeycomb. They consisted of a stack of air tubes with bulging ends that were sealed together so liquid could continuously flow between these tubes. This radiator design allowed for some very fancy grilles and ornate radiators similar to those used on the Model T Ford.

This cooling system was inefficient and lacked a secondary heat transfer surface, so the honeycomb radiator design eventually went away. Some vintage cars use radiator cores made from coiled tube, a less efficient but simpler construction.

 

 

 

The honeycomb design was replaced by the cellular or film design. In this design, the airways and secondary heat transfer surfaces were formed by a series of zigzag ribbons made out of copper. Each airway row was attached with a corrugated copper strip. The inward facing peaks of the corrugations acted as spacers for the air fins, while the outward facing peaks were dented across part of their width to form liquid coolant channels. This design was used because it dissipated heat quickly in a very small, light radiator.

Tube and Flat Fin Design Core

The next design used was the tube and flat fin. It used a series of inline or staggered coolant tubes that were assembled through a stack of continuous air fins spaced closely together. These air fins acted as the secondary heat transfer surface.

The coolant tubes were made from thin brass strips that had a flattened oval appearance. Thinner copper strips were used for the air fins. Louvers were used to promote turbulence in the airways. This core design was stronger than the early cellular or film design and was very significant during the 1940s, when the pressurized cooling system was introduced.

 

 

Corrugated Fin Design

The corrugated fin design (also known as the pack type) is the most common system. It is primarily used in today’s radiators for street, modified street, and race cars. Corrugated fin radiators are manufactured by both original and aftermarket manufacturers. This design uses alternate rows of brass or aluminum coolant tubes and airways made of zigzag ribbons of copper or aluminum.

The coolant tubes are made of a flat section, and the cooling fins may be louvered to promote turbulence. There may be two or more rows of coolant tubes, but the demand for lighter vehicles has led to the development of single-row versions. These have a finer pitch with less separation for corrugated fins to maintain a heat exchange capacity. This is because the heat radiated from the cooling fins is greater than that from the coolant tubes. This design is a conciliation between the cellular or film design and the tube and the flat fin design.

 

 

 

Radiator Materials

Originally, radiators cores were made from copper, and the collector tanks or header tanks were made of brass and bonded with solder. Copper and brass are very good materials for transferring heat, but they were heavier and are not renewable. This design was weak and the soldering usually worked loose from vibration and created leaks. So the copper and brass materials eventually gave way to aluminum.

Aluminum had been used for exhaust headers and collector tanks in commercial vehicles but not for radiators. In 1960, the Harrison Radiator Division of General Motors developed an aluminum radiator for the Chevrolet Corvette. This aluminum radiator used plastic tanks for production vehicles. The plastic tanks were lightweight, but they tended to crack, causing air (the enemy of cooling systems) to get in the system.

Today, auto manufacturers, including General Motors, Ford, Fiat-Chrysler, and Toyota, use aluminum for radiators primarily to reduce weight. Aluminum is not as efficient as copper for heat transfer, but the reduced weight and strength allows for a larger, more-efficient radiator.

 

Radiator Types

Automotive radiators have two basic types: downflow and crossflow. Currently both types are used for stock, modified stock, and some racing applications. There are also dual-pass and tri-flow radiators.

 

 

Downflow Radiator

The downflow radiator was commonly used in older vehicles, and it is still used in modified stock. The radiator core is attached to an upper header tank and a lower collection tank. The header tank takes care of the expanding coolant and provides a reservoir in case any coolant is lost. The collector tank collects coolant that is returned to the engine after the heat has been removed and is then pumped back into the engine.

The downflow radiator design can use a remote header or overflow tank that is mounted separately from the radiator. This guarantees that the radiator will always be filled with coolant. The header tank also reduces any mixing of air with the coolant entering the radiator.

The overflow tank is a reservoir for engine coolant that is heated to its boiling point and would otherwise rise up and blow out of the radiator. The circulating coolant is separated from the air in the remote overflow tank. The overflow tank creates a closed cooling system that is more reliable and useful than previous designs. As the temperature and pressure rise to the coolant’s boiling point under pressure, the cap spring activates and allows the heated liquid to flow up and into the overflow tank. The system is under pressure so the liquid will reach a higher temperature before boiling, further increasing the effectiveness of the system.

This overflow tank can also reduce the possibility of water pump cavitation erosion caused by low pressure at the water pump inlet. A filler neck together with an overflow pipe connection are generally provided on the overflow tank. The overflow tank can be a standalone system on an older vehicle that does not use an expansion tank; on newer systems, it can be used in conjunction with the expansion tank.

Crossflow Radiator

The crossflow radiator was developed because the automotive industry needed a radiator design that had a core that was low and wide enough to provide airflow through the lower grilles. General Motors invented the crossflow radiator in the mid-1960s to compensate for these new grille designs. It was first used in the Chevrolet Corvette.

 

This radiator had an inlet (header) tank on one side and an outlet (collector) tank on the other side to provide the radiator with the reserve of coolant and prevent aeration. In some applications, a separate header tank was connected to the upper end of the outlet tank. In other applications, the separate header tank was eliminated. To prevent aeration, the filler cap and the overflow parts are located at the upper end of the outlet tank because that is where air tends to collect.

Dual-Pass Radiator

The dual-pass radiator has the coolant pass through the radiator core twice before returning it to the engine at a lower temperature. This design allows the engine coolant to go through two thermal transfer cycles, lowering the liquid in versus liquid out temperature to a much larger extent than a single-pass radiator.

The dual-pass radiator is identified by the placement of the inlet and outlet pipes on one side of the radiator. You can also see the weld marks between the separate units. The dual-pass radiator provides a lower output temperature.

 

 

Tri-Flow Radiator

Traditional radiators only pass the coolant one time in the front of the fan. Eastwood manufactures a triple-pass radiator called the tri-flow radiator. It has the coolant pass through the radiator core three times to provide lower outlet temperatures.

The tri-flow radiator has two rows and a 1-inch oval tube core. Its unique coolant path routes the coolant through the radiator core three times. The path increases turbulent flow while passing the coolant in front of the fan three times. This system can help in some overheating situations.

 

 

Pressurized Cooling System

A limitation of most cooling systems is that the coolant should not be allowed to boil. The maximum amount of heat transfer is limited by the specific heat capacity of water and the difference in temperature between ambient temperature and the boiling point of water at 212°F (100°C). The thermal efficiency of the internal combustion engine increases with internal temperature, so the coolant must be kept at higher-than-atmospheric pressure to increase its boiling point.

When you pressurize the cooling system, the coolant can circulate at a higher boiling temperature, so that heat will be transferred more rapidly from the radiator through a greater or higher temperature differential between the two. This design will compensate for the lower atmospheric pressure (less than 14.7 psi) in high-altitude areas such as Denver, where the boiling point of the coolant would be lower and an overheat condition would be more likely.

The transfer of heat from the radiator is directly proportional to the temperature difference between the coolant and the radiator, so a pressurized system allows a radiator to be smaller but its design must be stronger to compensate. The increase in pressure at the pump inlet reduces the possibility of cavitation damage, as was previously discussed. Because the system has to be sealed, there is less coolant lost through evaporation and surging than if it were just vented.

Pressurized systems are more complex than vented systems. They are also more susceptible to damage because the coolant is under pressure. For example, minor damage in one of the radiator coolant tubes from a small puncture would cause the coolant to rapidly spray out of the hole. Failures of the cooling systems are one of the leading causes of engine failure.

Radiator Pressure Cap

John Karmazin of GM’s Harrison Radiator Division invented the radiator pressure cap. GM’s Buick Motor Division was the first to use the cap in 1939. The radiator pressure cap is a combination of a filler cap and a pressure control valve along with a vacuum control valve. It is placed at the highest point in the cooling system and seals against a seat in the filler neck of the radiator.

While the engine is running and the radiator pressure cap is in position, the cooling system will pressurize by pushing against a spring. This action takes place automatically when the coolant expands as it gets hotter. The reason for using this is to maintain the cooling system at a pressure that is above that of atmospheric pressure.

The radiator cap allows the engine’s coolant to expand and contract without allowing air to enter the cooling system. The upper seal protects the system at all times. After the engine warms and system pressure reaches the cap’s rated pressure, the spring compresses and coolant flows into the reservoir or coolant overflow tank. This allows for expansion of the heated fluid.

Water always boils at 212°F under standard atmospheric pressure (14.7 psi). If the coolant is under pressure greater than 14.7 psi, the boiling point will be higher. It will increase as the pressure increases. This occurs because the coolant molecules are compressed by the pressure and will have to vibrate more for the temperature to increase.

The radiator pressure cap increases the cooling system pressure, which increases the boiling point and prevents coolant loss. For every pound of spring pressure, the boiling point is increased by 3 degrees. Water boils at 212°F, and increasing the pressure in a closed system increases the boiling point beyond that. A cap rated at 15 pounds will increase the boiling point in a system by 45°F with a boiling point of 257°F (212 + 45). High-performance radiator pressure caps range from 19 to 32 psi. Original manufacturers can design engines with higher operating temperatures.

 

 

 

 

 

Radiator Cap Upgrades

Aftermarket radiators are upgrades to the OEM units, so you should pay attention to your radiator cap pressure rating. The coolant is under pressure to keep the boiling point as high as possible. That is why you want the highest pressure cap rating suitable for your application. Caps for older vehicles will most likely be rated for 7 to 12 pounds; newer vehicles will generally be in the 16 to 20 psi range.

If there is a leak in your system, higher pressure will push it out faster. The automotive cooling system is rated to a certain pressure by an extensive design process. The radiator pressure cap is designed to be the weak point in your cooling system so it can safely vent pressure. You don’t want to use a cap that is so resistant to venting pressure that it causes some other part of the system to become the weak point. The higher the system pressure the greater the stress on the entire system, particularly gaskets, seals, junctions, and seams. If you go very high above the OEM’s design pressure and the conditions are right, the hoses and even the radiator could burst.

If your cooling system is insufficient, it should be properly repaired and upgraded as necessary. Keep in mind that increasing the pressure beyond a couple of pounds above original spec is just not a good idea. The highest cap I have ever seen was 32 psi. In severe racing environments, you might see a higher pressure cap where you would have AN fittings and stainless steel–reinforced hoses, but I would follow the original designers’ cap pressure, which is based on the original system design. Contact the manufacturer who makes the cap or radiator to see what the qualifying points are for its radiator pressure cap to determine the integrity of your cooling system.

Closed Cooling System

In a closed cooling system, it is not necessary to inspect the coolant level as often as an open system because it is sealed. This is different than the earlier nonsealed system, where the coolant would simply drain to the ground from the overflow pipe just below the pressure cap. The closed cooling system uses an expansion tank, which is part of the pressurized section of the cooling system. It allows about 1 gallon of extra cooling system capacity.

The expansion tank is under pressure and will require a pressure cap of 16 to 20 psi. The pressure cap of the expansion tank should be the highest point in the coolant system. The expansion tank is designed so there is space in the tank for the coolant to expand. The expansion tank can also be used as a fill point for the system. If an expansion tank is overfilled, it will discharge coolant when the system is at operating temperature.

 

 

 

When an expansion tank is used, the radiator does not use a pressure-relieving cap. The expansion tank’s pressure cap acts the same as the regular radiator pressure cap.

When the engine cools down and the coolant in the system also cools, the drop in pressure will open the vacuum valve in the radiator pressure cap. Since the coolant in the reserve tank or expansion tank is vented to the atmosphere, it is now at a greater pressure than the coolant still in the cooling system, so the coolant from the expansion tank will now flow back into the radiator. The radiator pressure cap opens to the atmosphere through the vacuum valve so that the upper radiator hose will not collapse.

There were also early systems that used a recovery or reservoir tank. In this type of system, a hose from the reservoir tank went to a connection just below the radiator pressure cap on top of the radiator. A recovery or reservoir tank uses a vented cap and is not required to be above the cylinder heads. Its job is to hold the coolant that is discharged from the system’s pressure relief at the radiator pressure cap when the coolant is hot and expanding. When the system cools, the cooling effect creates a vacuum that pulls this coolant back into the system.

A catch tank was used to collect expelled coolant from the system. You should not confuse the recovery or reservoir tank with a catch or surge tank. The recovery or reservoir tank will either be plumbed at the bottom of the tank or have a hose internally that runs to the bottom so coolant can be drawn back into the cooling system. A catch tank is not under pressure and uses a vented cap. It features plumbing into the tank with a hose that goes back to the expansion tank.

 

 

 

 

While both a reservoir tank and a catch tank hold excess coolant, a reservoir will pull the coolant back in the system. Whereas a catch tank will hold the coolant until the vacuum valve in the expansion tank opens and coolant is sucked back into the expansion tank when the pressure is low, or in some applications it can be emptied.

Aftermarket Overflow Tank

Higher horsepower engines will produce more heat energy that will need to be dissipated by the engine coolant through the radiator. Generally the best way to improve radiator performance is to make it bigger. Yet you may not have enough space in a modified vehicle for a larger radiator plus the additional weight of the radiator. To assist in this situation, most high-performance radiators are made from lightweight aluminum and come in many different sizes and configurations.

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This Tech Tip is From the Full Book, HIGH PERFORMANCE AUTOMOTIVE COOLING SYSTEMS. For a comprehensive guide on this entire subject you can visit this link:

LEARN MORE ABOUT THIS BOOK HERE

SHARE THIS ARTICLE: Please feel free to share this post In Facebook Groups or any automotive Forums or blogs you read. You can use the social sharing buttons to the left, or copy and paste the website link:
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The size and the number of cooling fins or fin density and the coolant tube diameter can be manipulated to improve heat dissipation. More fins equals higher heat rejection, so why not make all radiators with the most cooling fins as possible? High fin density is not good for all modified vehicle applications.

The cooling fin count needs to be a balance of the heat dissipation and the amount of area that will be prone to clogging. Clogging reduces flow and cooling and is an issue if a vehicle is being used on a dirt or circle track. If the fin density is too high, it will increase the pressure drop in addition to restricting airflow, causing the pressure drop. This takes place with the more cooling fins in the lesser area for air to pass through and take away the heat.

 

 

 

 

 

 

 

Heat Rejection Needs

There are many factors in engine combustion and heat transfer that are common, such as engine operating mode, fuel air ratio, volumetric efficiency/mass efficiency, etc. The best approach to radiator sizing is to use actual full-load heat rejection data acquired from the engine original manufacturer. This is usually from dynamometer test data and sometimes can be done using computerized performance simulators. Some manufacturers perform final testing on a test track to determine if the radiator is the right size.

Heat rejection values of an engine within the same family can vary up to 5 percent, such as the GM LS1– LS5 series. So if you are using GM data, it’s important to get the most accurate information. Something that is just as important is the coolant pump flow rate over a range of engine RPM and temperature, which is generally obtained from the engine manufacturer.

Most OEMs consider this data proprietary and will generally not provide it. Internet searches usually will not yield this data either. The best approach is to write a very detailed letter to the engineering department asking for specific data for the engine you are using. The Chevrolet high-performance engines for the LT1–LT4 and the LS series are used in the Corvette, so you can contact the Corvette Action Center in Louisville, Kentucky, through its website corvetteactioncenter.com. Other aftermarket radiator companies, such as Champion Cooling Systems, BeCool, and U.S. Radiator, have blogs and helplines.

OEM Radiator Design and Testing

When an auto manufacturer designs a radiator, it has to first consider the coolant passage design for the cylinder head. Then, consideration must be given to the engine block, the water pump flow rates, and the thermostat function. All of these things are found when the engine is on an engine dynamometer in the test cell.

Radiator design is based on the amount of heat that needs to be rejected. The design process begins by sizing the radiator to meet the engine heat rejection for any possible operating range. Any internal combustion engine ignites the fuel-air under pressure to produce useful work but also with about 70 percent wasted heat. The wasted heat of combustion is transferred to the coolant through the cylinder wall and the cylinder head water jacket by conduction and convection. The coolant also picks up friction and lubricating oil heat. The heat of the coolant is transferred by forced convection to the atmosphere as the coolant is pumped through the radiator.

Next, designers size the radiator for maximum engine horsepower and load conditions. An engine that produces its maximum horsepower at 6,000 rpm at full load can have a heat rejection into the cooling system of about 6,200 btu per minute. Engine durability or performance are directly related to the coolant temperature, and you want to have a heat output and also want to be able to prevent any possible overheating due a poor design. You would need to design a radiator for the worst-case situation. Radiator design can start on the dyno, but it must be completed on a test track in the warmer western states. Most OEMs use hot-weather test tracks in Arizona. They can run their vehicles under various load conditions in extremely hot weather, which is a true test of an engine cooling system. They also commonly use Pike’s Peak as a test location.

Radiator Selection

When choosing a radiator, you have to consider horsepower, road speed, and loads that the vehicle will be placed under. The airflow through the system, including the air-conditioner condenser, is also a factor. Air flowing through the condenser results in an airflow restriction that must be considered in radiator selection. Other factors include dimensions, fin density, number of passes, number of rows, materials, and fluid.

Dimensions

Radiators used for high performance should be as thin and wide as the vehicle will allow. You need a wide and tall radiator with maximum surface area. If the radiator is too thick or has too high a fin density, the air will move too slowly through it to remove the heat from the coolant.

 

 

Fin Density

Fin counts are also a critical radiator-design component, but a higher fin density (measured in fins per inch) may make airflow more difficult and not necessarily work well for dirt track or some street applications. As the radiator fin density is increased, the efficiency generally goes down. High fin density provides good cooling, but it can restrict the flow through the engine, causing the pressure to drop. You need to achieve a balance between the number of fins and airflow.

Passes

There are single-, dual-, and triple-pass radiators. All downflow radiators are of a single-pass design, in which coolant moves from the header tank through the tubes to the collector tank at the bottom.

Crossflow radiator design can be single-, dual-, and triple-pass designs. When there are multiple passes through the radiator, the time the coolant is in the radiator increases and results in a lower outlet temperature. However, there is more restricted flow through the radiator, so it is extremely important that you have a high-flow pump in the system, usually somewhere in the 60 to 70 gpm at minimum.

Many of the performance radiator companies build radiators with a dual or triple core to obtain a maximum fin density. These radiators have the following features:

• Billet filler neck that reduces stress cracks or leaks and has large overflow tube
• Effective fin design available
• A CAB-brazed non-epoxy core construction that is repairable
• Aluminum components that are up to 50-percent lighter than copper, brass, or lead radiators
• Internal transmission cooler and upgraded internal engine oil coolers
• Most include OEM design brass drain petcock

Number of Internal Rows

Another factor is the number of rows of coolant tubes. There are two- and three-row designs. Tubes in all radiators are flattened to increase surface area that contacts the fins. Aluminum radiators use 1-inch-diameter tubes that are roughly 31 to 48 inches apart.

American-made radiators use thicker wall tubes that are less likely to fail under high pressure. Then why have aluminum radiators become so popular? One big reason is the potential for a significant weight reduction and lower material costs. Modified vehicle builders are also big on aluminum radiators for that reason, with a weight difference of around 10 to 15 pounds.

Radiator Materials

Aluminum is the material of choice today by most builders of modified stock or racing vehicles. It is lighter, stronger, and can have multiple pass designs. They also have welded tanks, which generally eliminates leaks and air ingress.

In the past, copper and brass radiators were used for good heat transfer rates. Copper has an excellent thermal conductivity rating. A copper fin’s thermal conductivity rating is about 50 percent higher than an aluminum fin. Brass, which is an alloy of copper, is not as good of a conductor as aluminum but is used for the tubes because of its strength. One problem with copper is that the lead solder used in older copper and brass radiators has a terrible thermal conductivity rating, which limits the efficiency of lead-soldered radiators. So some companies, such as U.S. Radiator, have instituted a newer process that improves efficiency by changing the flux and solder and its contact with the fins.

Some copper and brass radiators are less expensive than others due to their construction. The original radiators built in the muscle car era for GTO, Olds 442, Road Runner, etc. used 11/42-inch tubes. More modern radiator construction moved those centers closer together, with the same 11/42-inch tubes. This creates room for more tubes in the same-size radiator core. Each of these versions can be obtained in two-, three-, or four-row applications. As the radiators become denser, they become more expensive. However, the thicker the radiator, the more airflow will be reduced.

Aluminum radiators can be expensive, costing between $450 and $550. Yet, there are universal crossflow aluminum radiators with no mounting tabs that have either General Motors or Ford-style inlet and outlet hose configurations. These radiators are a two-row design with 1-inch tubes and come with a machined-aluminum filler neck welded into place. If you are willing to do some radiator mount fabrication, you can fit these radiators to many different applications.

Some of aftermarket radiators do not have an internal automatic transmission fluid cooler, so you may need an external transmission fluid cooler. When you use an external cooler, you may experience some high transmission fluid temperature in heavy traffic, so you may need to install a fan on your external transmission fluid cooler. You may also have to fabricate a shroud for this universal crossflow radiator to optimize airflow through the radiator.

 

 

Automatic Transmission Fluid Coolers

All OEM-built vehicles supply automatic transmission–equipped vehicles with an automatic transmission fluid (ATF) cooler installed in one of the radiator tanks. That is about 90 percent of production vehicles. Most of the high-performance radiators come equipped with an ATF cooler in the left tank.

The automatic transmission works harder when it is used for racing, it has added weight from a large-displacement engine, or it is used for towing. The transmission can get hotter, and heat is one of the major enemies of ATF. An aftermarket transmission cooler can keep your transmission from getting too hot, helping you get the best performance and long life out of it. Some drag racing radiators do not have a transmission fluid cooler. If you are running an automatic transmission that does not have one, you would need to add an auxiliary cooler.

When a transmission fluid cooler is used in the radiator, it is placed in the outlet tank, where the coolant has the lowest temperature. The auxiliary transmission oil cooler is generally an oil-to-air heat exchanger placed in front of the air-conditioner condenser or radiator. The transmission oil temperature is regulated by the airflow passing over this heat exchanger. The oil out of the transmission is plumbed through the transmission oil cooler hoses to the cooler then directed back to the transmission. This cooler helps provided additional cooling for performance driving conditions.

Some project vehicles cannot have the ATF auxiliary cooler in front of the engine cooling system radiator. If that is the case, there are three options: a remote mounted auxiliary cooler with its own cooling fan, a heat sink–style cooler, or a frame rail–mounted cooler.

 

 

 

 

 

Selection Example

When selecting a radiator, it should be as thin as possible and have the least number of fins per inch. You would most likely select a 0.7-inch-deep single-row radiator for your first choice to establish a performance curve.

Let’s say you are selecting a radiator for a high-horsepower crate engine such as a GM LS1–LS5 series or the new LT1 crate engine to be installed in a modified street vehicle, I would suggest the following:

• Select a heavy-duty radiator size that the OEM used with this engine in a production vehicle, such as the Cadillac CT5 or Corvette new LT1.
• Choose an aftermarket welded-aluminum dual-pass radiator that will fit along with dual electric fans with proper shrouding or a tri-flow triple-pass radiator with proper shrouding. You can consult with any of the radiator companies for selection advice.
• Install a high-capacity water pump (either mechanical or electric).

 

 

Radiator Inefficiency

Radiators can become inefficient or defective. This, in most cases, will lead to engine overheating. Let’s look at a couple of the more common problems.

Partially Blocked Radiator Core

If the outside surface of the radiator core is blocked by road dirt and debris, you will have much less air flowing across the core. This will mean the heat absorption will be low, which could result in overheating. You can clean out airways by applying air or water pressure from the engine side of the radiator. This will reverse the direction of normal airflow.

Partially Blocked Waterways

Corrosion on the internal metal surfaces of the cooling water jackets can act as a thermal insulator. This slows down or prevents the conduction of heat through the metal. The remedy is to reverse flush the radiator.

A matrix flow test will determine the extent of any internal restriction to coolant flow to the radiator. To perform the test, remove the hoses and temporarily insert a plug in the outlet pipe. Fill the radiator and container completely with water then remove the plug from the outlet pipe. Record the time it takes for the water and container to drain and compare it to OEM specifications.

Standard Cooling System Flushing Steps

1. Drain the system (dispose of the old coolant correctly).
2. Fill the system with clean water and flushing/cleaning chemical.
3. Start the engine and run until it reaches operating temperature with the heater on.
4. Drain the system and fill with clean water.
5. Repeat until the drain water runs clear (any remaining flush agent will upset pH).
6. Fill the system with 50-50 antifreeze/water mix or a premixed coolant.
7. Start the engine and run until it reaches operating temperature with the heater on.
8. Adjust coolant level as needed.

Reverse Flushing a Cooling System Steps

1. Flush the water through the radiator until it runs out clear.
2. If water does not clear in a few minutes, remove the radiator and turn it upside-down or stand it on one end so that you can flush it in the reverse direction to the normal flow. Tilt if necessary to bring the inlet at the top or header tank to the lowest point.
3. Use a garden hose into the bottom or collector tank to push water out the top or header tank of the radiator.

Written by John F. Kershaw, EdD, PhD and republished with permission of CarTech Inc

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