High-performance engines produce heat, and a bunch of it. Add horsepower and there’s a good chance you’ll need to upgrade the cooling system. As a rule of thumb, approximately half of the heat energy generated by the engine goes into the cooling system. Put too much heat and pressure into the system and your reward will be a big puddle of coolant on the pavement—and possibly a cooked engine.
It’s up to the radiator to spare you such a fate. Today’s radiators are a far different breed of cat when compared to yesteryear’s copper-brass examples. As part of a good cooling system, a modern radiator will keep your car from running too hot, especially when summer’s heat rolls around.
We spent some time with the experts at DeWitts Radiator to learn more about what makes a good radiator and to unlearn some old wives’ tales.
The Big Tank
Think of a radiator as a big tank that allows hot coolant to come in contact with cool outside air. Coolant from the engine runs through a system of thin-wall tubes in the radiator core. Heat dissipates from the coolant through the tube walls and passes to fins that are in contact with the tubes. The heat is transferred to the air passing through the fins. The coolant then goes back to the engine.
Most radiator cores consist of layers of tubes and fins, headers, and side plates brazed together. For example, a four-row radiator has a core with four rows of tubes. The number of tubes in each layer can vary based on the application and radiator material.
Copper-Brass vs. Aluminum
Good old-fashioned copper is actually a good material choice for a radiator, offering superior thermal conductive properties than aluminum. The issue with copper-brass radiators is their construction. The copper tubes are bonded to the fins with lead solder, which has extremely poor heat transfer properties. DeWitts notes that independent testing shows aluminum radiators can lower engine temperatures by as much as 30 degrees compared to their copper-brass equivalents.
Aluminum radiators are more efficient because they have more tube-to-fin contact surface area than an identically sized copper-brass radiator. Part of this is due to the fact that aluminum radiators have fins that are wider, closer together, and shorter in height. This results in more layers in the same given space. A two-row aluminum radiator can reject more heat than a copper-brass radiator of similar size made with four rows of tubes.
You may have heard that fin count is important, and it is. Typically, an aluminum radiator will have between eight to fourteen fins per inch. As fin count numbers increase, the more heat radiates into the airstream flowing through and around the radiator.
Tube Size
DeWitts builds their standard aluminum radiators with one-inch diameter tubes. A radiator with a double-row core of one-inch tubes is equal to a five-row copper-brass unit. It also offers almost double the heat rejection of a single-row aluminum unit.
It is possible to build a copper-brass radiator with the same methods used to build aluminum radiators. DeWitts tells us it might even work a bit better than a comparable aluminum radiator. But there’s a wee catch—that copper-brass radiator would weigh approximately 90 pounds!
There’s often a difference in tube dimensions between American-made and offshore-built radiators. The American standard for performance aluminum radiator tubes is one-inch wide. Imported radiators are typically built with smaller 0.6299-inch tubes. That means less tube-to-fin contact surface and less cooling capacity.
Tube Construction
There’s some difference of opinion when it comes to tube construction. For example, the use of extruded cooling tubes has become popular. Often found in high-pressure oil coolers and charge air coolers for superchargers, extruded cooling tubes are manufactured by heating and pressing aluminum material through special dies to a specific shape.
The major advantage of an extruded tube layout is higher burst pressure capacity. The heavy wall thickness and internal trusses provide the strength needed to handle higher pressures. Considering most automotive cooling systems operate in the 10-20 PSI range, this quality is not really a benefit here.
DeWitts says a radiator with extruded cooling tubes will be heavier, run hotter, and have a higher pressure drop than a standard double-row aluminum radiator. It can be difficult to form these tubes with thin wall thickness dimensions. Typically, the wall thickness for extruded cooling tubes ranges from 0.020- to 0.040-inch. This is actually too thick for efficient engine cooling.
DeWitts and most other manufacturers build their radiators with roll form tubes. They are the gold standard in automotive cooling because their thinner walls (0.010-0.015-inch on average) will transfer heat better and reduce unnecessary weight. Roll form tubes can handle pressure as high as 45 PSI without tube distortion. That provides a 300% pressure safety factor when pressurizing the cooling system to 15 PSI.
There has also been a trend to use even thinner tubes and fins to save money on material. DeWitts doesn’t subscribe to this practice.
“We have stayed with proven 0.013-inch and 0.015-inch wall tubes while some companies are using materials that are 0.003-inch thinner,” they explained. “We also use 0.005-inch thick fin material when others are using 0.003-0.004-inch material. This may not sound like a big difference, but our design is proven to hold 60 PSI without tube distortion and 100 PSI without bursting.”
Downflow vs. Crossflow
There are two basic radiator configurations. Crossflow radiators have the tanks on either side of the core with the radiator tubes running horizontally. Downflow radiators have the tanks on top and bottom of the core with the radiator tubes running vertically.
Most cars through the 1960s, classic trucks, and many muscle cars used downflow radiators. Crossflow radiators were adopted in the late 1960s and early 1970s to accommodate lower hood profiles.
There is a lot of back and forth about which radiator design cools better. Given the same size core and construction, both designs offer the same amount of cooling capacity. Crossflow radiators are a better choice for big horsepower engines running at high RPM. That’s because the radiator cap is positioned on the low pressure (suction) side of the system. This prevents the pressure created by a high-flow water pump from forcing coolant past the radiator cap at high RPM. This goes double if the engine is in a car with a small grille opening.
DeWitts makes high-capacity downflow radiators for cars and trucks that were factory-equipped with one. They’re direct-fit so they’re a drop-in installation. Paint one black and no one needs to know its aluminum.
Cooling System Pressure
Pressurizing the cooling system raises the boiling point of the coolant three degrees for every one pound of pressure. This does not have anything to do with how your cooling system will perform. It only sets the point at which your coolant will boil. For example, a coolant mixture of 50/50 water and antifreeze has a boiling point of 238 degrees. Pressurizing the system to 15 PSI will raise that point to 283 degrees but will not change the actual coolant temperature. Radiator caps are available with ratings of 7-20 PSI; DeWitts recommends using a cap rated between 13 and 15 PSI.
It’s The Water
DeWitts emphasizes the quality of the water you use is more important than the brand of coolant, especially with aluminum radiators. Aluminum is very sensitive to minerals and chemicals in water, so DeWitts recommends a mixture of distilled water and coolant. Using a pre-mixed extended-life coolant will work as well since they are made with distilled water.
For even more information on selecting a radiator, be sure to read our How to Choose a Radiator article.
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