Cooling-System Tips
While the cooling system may seem simple, consider not only the variables of coolant flow, airflow, and radiator efficiency, but also how other engine systems affect cooling. If the charging system is lame, your electric fan won't spin as fast. If the ignition curve is slow, that will affect cooling. We've assembled a series of tips and tricks that can often make the difference between an overheating monster and a docile street machine that can handle gridlock in 110-degree weather.
*Ignition timing has a direct effect on cooling-system performance. Retarded ignition timing begins the combustion process later in the cycle and makes heat. Initial timing numbers of 12 to 16 degrees and a curve that's all in by 2,500 rpm is a good starting place.
*An electric fan placed on the engine side of the radiator (as a puller) is always more efficient than a pusher fan. However, additional airflow can be created by using a second pusher fan on the front of the radiator.
This '57 Chevy's builder went to extraordinary lengths to ensure that all the air entering the grille would travel through the radiator. Building small-block off-plates between the radiator and the core support to direct all the air through the radiator will accomplish the same thing.
*Third-generation ('82-'92) Camaros came with an airdam placed directly under the radiator, which on older, high-mileage cars might be damaged or removed. These airdams are essential to create a low-pressure area behind the radiator to move air through the radiator.
*Jason Schmidt is an engineer with Spal, and he told us about a customer who had connected the power wire for a large electric fan directly into his fusebox. When large fans start, they can pull as much as 80 to 100 amps for 0.10 second. This large current draw pulled the voltage down far enough that the engine died. Wiring the power lead for the fan through a relay that sources power nearer the alternator cured the problem.
*The ideal tip clearance for engine-driven fans is 11/42-inch with the fan blade extending roughly halfway into the end of the shroud. This will create the greatest amount of air movement past the fan.
*Most engines are thermally more efficient at a coolant temperature of 195 to 200 degrees Fahrenheit. Pressure is also a critical function of coolant efficiency. A typical street-car cooling system operates at 15 psi. This pressure also increases the boiling temperature of water. As a rough rule of thumb, for every 1 psi of cooling-system pressure, the boiling point of straight water will rise between 2 and 3 degrees. Water boils at sea level at 212 degrees Fahrenheit, but at 15-psi gauge pressure, water boils at 250 degrees Fahrenheit.