Making big power with today's high-performance parts is relatively easy. Just go online, choose the parts that match your performance target, andwait for the goodies to arrive. But after those extra horses are stabled under your hood, you may notice your temp gauge is running hotter than before. More-powerful engine combos, lower rearend ratios, and high-stall converters all contribute to greater engine heat. Without the proper cooling components, out-of-control engine heat can cause head gaskets to blow, parts to seize, and blocks to crack.
A better idea is to match the cooling system to your engine combo and vehicle use. This means installing a system complete with adequate frontal airflow, correct radiator sizing, a properly selected thermostat, a good water pump, a fan, and a shroud. Understanding which components you'll need and installing them properly will keep your engine running cool and your performance hot.
The Liquid System
Most modern passenger-car engines are cooled with a liquid, typically water and coolant (for street use). This circulates (powered by a water pump) inside the engine through water jackets and out through an upper radiator hose, where it enters the radiator core to be cooled. The radiator core's numerous passages, called rows or tubes, have cooling fins attached. As the hot liquid travels in one direction through the radiator core, moving air (drawn by the engine fan and vehicle movement) lowers the liquid's temperature dramatically by heat transfer, and it is cycled back into the engine.
Open & Shut Case
Thermostats regulate the flow of the cooling liquid after the engine's temperature has reached a set level. This is done largely to allow quicker warm-ups. For most engines, thermostats are available from 160 to 195 degrees F. Some newer thermostats are available in even higher ratings.
Switching from one thermostat rating to another may raise or lower the engine's operating temperature. For colder-weather operation, a thermostat with a higher rating of 195 is usually the best choice. If a colder thermostat, such as a 160, is used in a cold climate (below 60 degrees F), the vehicle's engine may never reach operating temperature and the heater may never produce warm air. Additionally, the condition may increase engine wear due to colder (and thicker) oil, the fuel not burning as completely, and possibly smaller engine clearances.
In warmer climates, a 160 or 180 thermostat may keep the engine temperature down by a few degrees as long as the cooling system is efficient enough to maintain the colder operation. If the cooling system's efficiency is marginal at best, the engine may run at the same higher temperature, in spite of the thermostat.
A fan clutch and accompanying seven-blade fan work well to keep medium-horsepower musclecars cool. There are two types of fan clutches (thermal and nonthermal), both fluid driven. The better one is the thermal type and is identified by its bimetal spring (arrow). It engages the fan when air temperature reaches about 170 degrees F, measured behind the radiator. Thermal types run the fan at 60-80 percent of engine speed (when engaged). This also improves fuel economy at lower temps. The lower-cost nonthermal type is almost always engaged.
Crossflow vs. Downflow
Until the late '60s, most Chevrolets used a downflow-style radiator, identified by an upper tank, a downward-flowing radiator core, and a bottom tank. Modern-style radiators (after the late '60s) are of the crossflow design, featuring a tank at each end and a core that flows across, and have been used in later-model cars because they allow automotive designers to build lower and more aerodynamic body shapes.
Crossflow and downflow radiators provide almost identical cooling results given identical radiator size and efficiency. What is important, though, on any radiator (especially one used with a high-performance engine) is that the upper and lower hoses are attached to the radiator at opposite sides. This arrangement forces the liquid to travel from the inlet hose diagonally across the radiator to the lower hose, maximizing heat transfer from the liquid.
The smaller the water-pump pulley, the faster the pump turns. If the pulley is too small the pump speed will be so high that there will be cooling losses, because the liquid will never have enough time to cool in the radiator. Our friends at GM Powertrain have told us that, on average, a water pump requires about 12-15 hp to operate at 6,000 rpm. Most modern water pumps use pulley sizes that rotate the water pump at 10-40 percent above crankshaft speed.
Take No Static
Inside your cooling system lurks the potential for electrical charge. If it occurs, aluminum-damaging electrolysis can take place, causing rapid component corrosion. The condition usually occurs if there is a defective or missing ground strap to one of the numerous potential electrical sources. To minimize this risk, make sure your engine retains good ground straps and don't be tempted to ground electrical items to the radiator.
To test for possible electrolysis hazards, connect the negative lead of a volt/ohm meter to the battery ground. Next, insert the positive lead into the coolant inside the radiator without contacting the opening. If you find more than 0.10 V, there is electrical current flowing through the system. To isolate the circuit, have a friend turn off-and-on various electrical devices or remove fuses (with the car running), while performing the test.
An engine's cooling fan provides the most benefit when the vehicle is standing still or moving at slow speeds. At highway speeds the incoming air generally provides enough movement through the radiator to keep the engine cool. Most of today's cooling systems utilize electric fans instead of the older engine-driven fans. Electric fans offer car builders tighter engine packaging, no parasitic loss (unlike the power-robbing beltdrive system), and improved fuel economy. When an electric fan is installed in front of the radiator it's called a pusher, and behind the radiator it's called a puller. Because a pusher fan impedes incoming airflow through the radiator core, it is generally less efficient than a puller fan.
Mechanical fan-blade systems (typically found on musclecars) can offer reasonably good airflow as long as a good six- or seven-blade fan is used with a shroud. However, when mechanical fans are coupled directly to the water pump, they can require lots of horsepower to rotate. To minimize parasitic loss, a clutch-driven fan, which is never directly coupled to the engine, can be installed so that less power is required to turn the fan blade.
Fan blade shape plays a role in cooling efficiency too. A straight-blade fan often moves the most air, but is usually very noisy. Curved-blade fans are usually quieter, but generally flow about 10 percent less air than a straight-blade fan.