Getting Engaged
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.
Turn Here
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.
On average, the more fins per inch the better the cooling efficiency (more surface area to transfer the liquid temperature to air). Radiators should be mounted so that obstructions at front are minimized, allowing maximum airflow across the fins. | 
Engine-driven fans tend to operate most efficiently when the blades are positioned halfway in the fan shroud. | 
Quick Cooling System Notes
The cooling system should be flushed at least every two years.
* Check the belts, hoses, and radi-ator cap.
* Dragstrips require a coolant recovery container to catch any coolant that is purged out of your radiator.
* A pressurized radiator cap increases the pressure in the system to raise the boiling point. Pressure caps also incorporate a relief valve so that as the radiator cools, air is allowed to enter the system. |