It’s no big secret that big horsepower means increased heat. But high performance engines, like other internal combustion powerplants, aren’t really all that efficient. Roughly one-half of the total heat energy produced by an engine is not put to work, but simply transferred back to the cooling system. If your cooling system—especially your radiator—is not up to snuff, that heat won’t be properly dissipated to the atmosphere. That can leave you stuck on the side of the road with coolant burbling out of your radiator.
Here’s what happens to the coolant inside your radiator. As the coolant approaches its boiling point (for example, the boiling point of plain water at sea level is 212 degrees F), internal pressure begins to build. Since the cooling system is closed, the pressure continues to build without any opportunity to escape. As that pressure increases, so does the coolant’s boiling point.
If coolant temperature continues to rise and pressure increases past the radiator cap’s pressure rating (measured in pounds), the radiator will boil over and makes a mess. If the radiator boils over when you’re on the throttle and coolant gets under the tires, you know what happens next.
The Radiator Explained
The radiator is basically a huge tank that allows large amounts of hot coolant from the engine to come in contact with an equally large amount of cool air. The coolant is first forced into the radiator side tank (or upper tank if it’s an old fashioned non-crossflow system). The coolant makes its way through rows of very small copper or aluminum tubes in the radiator’s core, where it is cooled by air flowing over and beside the tubes. The heat is transferred from the tubes to fins that are in contact with the tubes. As air passes through the fins, the heat is carried away. The coolant then goes into the radiator’s second side tank and is returned to the engine.
The actual number of fins on the radiator is very important. As a rule of thumb, a conventional radiator will normally have 8-14 fins per inch. When more fins are added, the radiator can dissipate more heat to the surrounding air. The downside of more fins is the radiator is more easily plugged with bugs, dirt, and other gunk that reduce its efficiency.
Aluminum vs. Copper/Brass
Most modern radiators are made from aluminum. An aluminum radiator is more efficient and weighs up to one-third less than a comparable copper/brass radiator of the same dimensions. The main reason for aluminum’s greater efficiency is the ability to use wider tubes in the core. Larger tubes mean more tube-to-fin contact surface area (up to 20 percent over copper/brass), which provides better heat dissipation. That’s why an aluminum radiator with two rows of tubes can out-cool a copper/brass equivalent with four rows of tubes by as much as 30 degrees F.
That’s not to say there isn’t a place for a copper/brass radiator. They’re a must if you are restoring a classic vehicle or a 1960s-70s muscle car to stock or near-stock specifications. But if you’re turning up the horsepower wick, aluminum is where it’s at. And with the selection available today, there’s an aluminum radiator for just about every vehicle.
For even more information on selecting a radiator, be sure to read our How to Choose a Radiator post.