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by Steve Jack
Concept One Pulleys
Jackstands at Old Cars Only


Preface…The proper cooling system design and maintenance of today’s high performance streetrods, muscle cars, and classics cars is critical every owner to know and understand. The prolific addition of horsepower building goodies has taken many a car to the edge when it comes to adequately cooling the engine. A higher horsepower engine at idle will require more fuel which in turn means more heat to dissipate! This has also been exacerbated by the addition of air conditioning, closed engine compartments as well as the want to cruise in traffic at anytime and any conditions. With today’s aftermarket cooling products, there are no excuses for not being able to drive your favorite hotrod in the warmest of weather, to traffic-laden cruise-ins with the air a’blowin without the engine overheating! This is also a safety issue, whereas no one wants to get stuck in a high traffic area with an overheating car, which can be not only frustrating, but also dangerous territory on the side of a busy interstate.

The following list is a compilation of general suggestions to keep your cool ride on the cool side.  Since there are many derivations of engines, cooling systems, parts and designs, it is impossible to address every situation here. So, this is not a perfect solution to every cooling situation, just basic good sense and science for your ride! Enjoy!


  1. The aluminum radiator is the best overall product on the market for the dollar today. 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.  But, the choice of aluminum construction will outperform their copper/brass counterparts quite easily even though copper is a better conductor of heat. Aluminum construction overtakes the copper with more surface/fin area available for heat exchange. A typical 1.25”, two-row, aluminum radiator will outperform 4 or 5 row copper/brass brethren. Larger tube construction also offers higher heat dissipation, stiffer structure due to the aluminum welds and material strength, making for a less likely leaky situation due to torsion and vibration stresses. Also, the fact that more, if not all-modern cars are implementing aluminum radiator technology, more vendors are competing in this product line making for very attractive consumer pricing.
  1. Basic chemistry teaches us that pure water is the best coolant. 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 double the amount of BTUs per unit volume than the mix typical antifreeze (rated at 0.5).  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. The application of pressure in the system through the normal expansion of gas/air during heating is the natural solution to keeping the water from boiling away. A 10-psi pressure on the cooling system raises its boiling point to 239 degrees F with just water.  Only use the amount of antifreeze that your geographic region (for purposes of freezing) dictates!  I recommend only 20% in regions or seasons that don’t have to worry about freezing.  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 air production, 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!
  1. Utilize high-pressure radiator caps, whereas they serve no dynamic functional purpose other than to keep the coolant in and under pressure when the natural expansion of 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 14 lb cap for your system, whereas many systems will build at least 12 lbs under normal expansion. Keeping coolant in the system is one of the most important things you can do to prevent disaster!
  1. 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. A good analogy of this phenomenon, albeit on a grand scale, is the experience of jumping into a lake when the surface water feels warm, but just a few feet down, the water is significantly cooler. This is due to laminar flow or inadequate mixing. The same thing will happen in a radiator tube when all the water does not get mixed/cooled and significantly degrades the system’s ability to dissipate heat. 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.
  1. Use a high performance water pump.  These pumps move more water 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 long time 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. Stock water pumps are generally okay for stock engines, but are antiquated technology by today’s standards. The high performance pumps are a step up in cooling technology and reliability.
  1. 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 stock levels) are recommended. The benefits are higher coolant flow.
  1. 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.
  1. Tune the 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. 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.
  1. Utilize a quality mechanical 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 can 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/CFMs) is by performance ratings in running DC watts/amperage, given that most automotive fans are mechanically designed similarly.  Most applications will require at least a 16” fan that produces around 2000+CFMs and will require 18+amps (~240watts).
  1. 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…..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. 

Emergency actions that are called for in traffic when the temperature reaches epidemic proportions can be several. First, what is too hot? Contrary to popular believe you don’t have to consistently run below 200 degrees for a functional and effective cooling system. Ranges can vary between 170 degrees to 220 degrees.  Properly designed systems and accurate metering will indicate within a few degrees of the thermostat opening temperature. In certain conditions a properly designed system can be stressed to beyond the thermostat opening but as long as the system is stabilized at an acceptable level and still functioning, the system is adequate for the time being, but diagnosis of the problem that causes this should be undertaken. Don’t open the system when it is hot! Not only is this dangerous, but it removes all the friendly pressure and the system will not operate properly if closed back up before completely cooling down. Let the system completely cool and add water appropriately, if it is expelled.  One other trick is to turn your heater on high, which will help dissipate heat in an emergency situation! When in a line of traffic, keep at least a car length or two in between you and the guy in front. Modern cars throw off a lot of heat backwards and additional space can mean the difference of 30 to 40 degrees in incoming air to the radiator. In an emergency situation a bottle of water poured on the radiator will help reduce temperatures. Don’t wait for things to get out of hand forcing you into a perilous position for your car and especially yourself!

In conclusion, remember the high-five: high water content, high coolant flow, high radiator surface area, high pressure and high airflow. By following these basics, your ride hopefully will be forever coooool!

Steve Jack
Concept One Pulleys
Jackstands at Old Cars Only

Last Update: 05/29/03 Hits:

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