Fan-tastic
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.
A 50/50 mix of coolant to water is good for -34 degrees F ambient temp. These testers are available from most auto parts stores. | 
Brass freeze plugs (shown) last longer than standard steel plugs because the brass cannot be attacked by rust. What's unfortunate about this particular engine, though, is that the block has cracked (arrow), most likely because the engine was not protected with the proper blend of antifreeze. When water freezes it expands, and not even the cast-iron sides of an engine block will stop its progress. | 
In general, the best operating range for a performance engine is between 180 and 210 degrees F. If your engine is operating hotter than this range, inspect your cooling system. Clogged radiator cores, faulty fan drives, missing shrouds, stuck thermostats, inoperative electric fans, or blown head gaskets can cause higher-than-normal readings. If the engine is losing coolant but you can't find the leak, use a pressure tester to inspect the system. Some small-block Chevys leak coolant at the rear sides of the intake manifold. You may need a mirror to check this spot. Do this just after the engine is stopped, because after the engine sets for 30 minutes or so the leaking coolant can evaporate. |
The thermostat is always installed so that the pointed side (arrow) faces away from the engine. | 
Since the early '90s GM has been using 180-degree-F thermostats (80-82 degrees C) positioned on the water inlet side of the water pump at the lower radiator hose. This was done because water traveling from the radiator's lower hose is typically at a constant and moderate temperature. Consequently, the thermostat does not oscillate as often. | 
The small-block Chevy Edelbrock Victor water pump (right) incorporates computer-designed pump passages to provide more even liquid flow with higher velocity at all engine speeds. The impeller is CNC-machined and provides far better cooling performance than the crude stock unit (left). The $150 Edelbrock pump (EDL-8811) is available from summitracing.com. |