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1. Today's quality, large-tube, high-density fin aluminum radiators are the best overall product on the market for high efficiency cooling. This is not to say that the radiators made from copper/brass/solder are not good and if you have one that works, don't go out and change for the sake of change. For higher performance and more efficiency, the choice of aluminum construction with their larger total cooling area will outperform their copper/brass counterparts quite easily even though copper is a better conductor of heat. The aluminum design and construction overtakes the copper models with more total surface/final area available for heat exchange and larger elongated tubes for more flow and turbulence. A typical 1 or 1.25 inch, two-row, aluminum radiator will easily outperform their 4 or 5 row copper/brass brethren. The inherent large-tube construction offers higher shear heat dissipation and stiffer structure due to the aluminum rigidity and aluminum welds making for a less likely leaky situation due to torsion and vibration stresses. To corroborate this, notice that most, if not all OEM applications are now aluminum construction. This is for not only weight but moreover their high efficiency footprint.
2. Use a high performance water pump to increase the coolant flow. These pumps move more water (up to 77GPM at cruising speeds) and provide higher pressure to help in the reduction of hot spots, reduce cavitation and take less horsepower to do such. Contrary to popular believe and a long time industry myth, slowing the coolant through the radiator does not improve heat dissipation! I can't emphasize this enough. This is a widely held myth that is completely contrary to the laws of heat conduction physics. The higher the flow, the more heat will get absorbed and dissipated. This means that stock water pumps are generally okay for stock engines, but are antiquated technology by today's standards for high performance use. The high performance pumps are a significant step up in cooling technology and reliability.
3. Do not use "under drive" pulley sets for the street! For street driven vehicles, stock pulleys and preferably "overdrive" pulleys (that will spin your accessories over the crankshaft speed) are recommended. The benefits are higher coolant flow under idle and slow speed conditions. New high flow/volume pumps have as much as 50% higher flow rates at idle by integrating a high performance "overdrive" pulley systems that are now available. If utilizing electric water pumps, use ONLY the high output models (55GPM) only and these are marginal for street use. You will find yourself hunting for more output when under loads and sometimes while just cruising with high hp applications. Some cruising situations can call for 60GPM or more and the electric models just can't provide that. However, a high efficiency radiator will help alleviate some of this requirement flow requirement.
4. Use high water content coolant. On the coolant absorption front, basic chemistry teaches us that pure water is the best coolant, period. The common chemistry yardstick that says that it takes 1 BTU to raise 1 pound of water 1 degree F* is a specific heat number index. Pure water is assigned 1.0. Conversely, a 50/50% mix of a typical antifreeze product and water has a tested specific heat number range of 0.5 - 0.7, depending on product additives. This means that pure water will remove about 50% the amount of BTUs per unit volume than the typical antifreeze mix. Simply, the more water content, the more heat gets taken away! Do not confuse this with the boiling point of water. Pure water will boil at a lower temperature than that of a mix of water and antifreeze, as well as freeze at a higher temperature. Only use the amount of antifreeze that your geographic region (for purposes of freezing) dictates! I recommend about a 33% in regions or seasons that don't have to worry about freezing, but add anti-corrosion additives to complete the perfect concoction. Also, distilled water is best for radiator use and has no mineral content or solutions to deposit in or clog a radiator. This is NOT the same as de-ionized water! Tap water can do in a pinch with little harm, if any, just don't make it a habit. The use of surfactant/wetting agents (alters the surface tension of coolants) helps alleviate trapped air, cavitation, and the prevention of hot spots. This is reason enough alone to add them as insurance. These wetting agents will also cause the coolant to absorb heat at a faster rate, which means that in higher flowing systems more heat is carried over a time period than in a conventional system. This is only effective if your water pump increases the flow and the radiator can remove the additional heat when presented with such. Only use the wetting agents as directed, this is not a case where more is better!
5. Run vacuum advance! This will aid idle/low speed cooling situations. The exact advance for a " perfect" condition depends on other factors such as idle speed, compression, cam, head construction that enter into the "perfect" calculation. A static advance of 10* BTDC and a vacuum kicker of another 10* is typical and ideal. This has to be full-time manifold advance….not ported.
6. Tune that carb! Usually an engine that makes too much heat on the move/cruising is the result of a too lean condition in main jetting. A too lean idle will also produce more heat than a correct idle mixture. Other subtle signs of too lean of mixture are header/manifold discoloration (esp. on chrome), glowing exhaust headers/manifolds, significant heat build up in engine compartments, detonation, and vapor lock. This "tuning" aspect is usually not a factor on fuel-injected engines whereas computer software regulates the mixture, if properly programmed. If you have an injected/computer engine that is having cooling problems at speed then other factors such as coolant flow and airflow may be suspect moreover than mixture considerations.
7. Utilize high-pressure caps! Radiator caps serve no dynamic functional purpose other than to keep the coolant in and under pressure when the natural expansion of coolant and trapped gases takes place. Contrary to popular believe, the addition of a high-pressure cap does not necessarily increase your systems likelihood of building any more pressure. Utilize at least a 12 lb cap for your system, whereas many systems today will build at least 12 psi of friendly pressure under normal expansion and rpm conditions. Keeping coolant in the system is THE most important thing you can do to prevent disaster! Therefore, higher-pressure caps are an important "must" change to your system if you are running higher peak rpms, high-volume water pumps, and/or larger capacity systems and certainly if you are running higher operating temperatures of 170 degrees or more. All of these mentioned changes create more pressure at the cap. The old 7lb cap will NOT suffice for a high performance cooling systems and even the old stock systems can easily withstand a 12 or 14 psi cap!
8. Always run a thermostat. Removal of the thermostat degrades the mixing or turbulence (non-laminar flow) from the entrance to the radiator and will reduce the efficiency of the radiator. This turbulence is what makes sure that every molecule of water gets cooled as evenly as possible making for the best heat disposition. The changing of a thermostats will not help your engine cool better if your running temperature is consistently above the opening point of that thermostat. For example, changing to a 165 degree from a 195 degree thermostat, when you are consistently running over 195+ degrees, will not improve your cooling or reduce the final running temperature under the same conditions. The thermostat just opens sooner and may slightly prolong the rise to the same point. Look to another cooling issue(s), if that is a problem. Balanced thermostats are the best for accuracy and will not fail in the closed position.
9. Utilize a quality fan, clutch and shroud. They are a threesome act for effective cooling. The absence of a shroud can cut CFM production in half. The use of cheap flex-fans on high performance engines is not a good choice for cooling or reliability. A quality thermo-clutch is a must if you don't want to fling that fixed fan at warp-like speeds and seriously degrade peak power. Engines that all of a sudden run hot at idle or slow speeds equipped with clutched fans may be experiencing the loss of the clutch at low RPMs. The use of electrical fans is becoming prolific in rods, morphing from their popularity in modern-day autos. These fans are as reliable and actually produce more airflow at idle and slow speeds than that of any mechanical unit, making them excellent performers for heavy traffic and warmer climates. Do your homework when selecting a quality electric fan. The general yardstick of the fan's ability to do work (move air or CFMs) is by performance ratings in running DC watts/amperage, given that most electric automotive fans are mechanically designed similarly. Most applications will require at least a 16" fan that produces around 2500+CFMs and will require 20+amps (~250watts) at the very least. For you real heat producers, higher twin fan combinations are available from Spal or Derale and large fans such as the Mark VIII and others can move up to 4000 cfms, but take a whopping 40amps to accomplish this task. The additional electrical loads will require the alternator and some wiring to be upgraded as well… beforewarned!
10. Properly ventilate the engine compartment. It's not so much as the ambient temperature is concerned, but the flow of air in the compartment to allow the airflow through the radiator. Simply, with pressure behind the radiator, it won't accept cool air from the front therefore degrading the efficiency of the radiator. The modification of the front a car can contribute to the build-up of pressure behind the radiator and cause cooling problems at speed. The engine compartments of street rods can fall prey to this as well.
Happy Summer Cruising!