by Steve Jack
Proper cooling system design of today’s hi performance streetrods, muscle cars, and classics automobiles is a critical science for every owner to know and understand. The prolific addition of horsepower building goodies has taken many a car over the edge when it comes to properly cooling the engine. This has also been exacerbated by the addition of air-conditioning, closed and cramped engine compartments as well as the want to cruise in traffic at high ambient outdoor temperatures. With today’s aftermarket products, there are no excuses for not being able to drive your favorite hotrod in the warmest of weather, to the farthest cruise-in, with the air a’blowin, without the engine overheating! I also consider this a safety issue, whereas no one wants to get stuck in a high traffic area with an overheating car. This can be not only frustrating, but also dangerous territory…especially on the side of a busy interstate.
The following list is a general compilation of suggestions to keep your cool ride on the cool side. Since there are many derivations of cars today and so many different combinations of parts, it is hard just to address every situation. So, be forewarned…this is not an end all to every cooling situation, just basic good sense and science for your ride!
- If you are designing/redesigning a cooling system for your car, the utilization of the aluminum radiator is the best overall product on the market for the dollar. This is not to say that the radiators made from copper and brass 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 media will outperform their copper counterparts quite easily even though copper is a better conductor of heat. What is a lesser conductor of heat (aluminum) makes up with more surface area available for heat exchange. A 1.25″ two-row aluminum radiator will cool just about anything up to 450hp (depending on size of course) if designed correctly and will outperform most 4 or 5 row copper brethren. Not only does aluminum offer a great deal more surface area for cooling, but also are more rigid structures making for a less likely leaky situation. Also to the credit of this technology and the fact that more modern cars are implementing aluminum, more and more vendors are competing in this product line making for very attractive pricing. (When running an aluminum radiator or any aluminum parts in contact with the water jacket, make sure to run a sacrificial anode (usually zinc) to prevent the electro-displacement of the aluminum. This will save the aluminum parts, in short.)
- Only use the amount of antifreeze that your demographic region dictates. Basic chemistry tells us that pure water is the best coolant, period. The specific heat of water is 1.0. This is the common chemistry yardstick that says that it takes 1 BTU to raise 1 pound of water 1° F and is assigned the 1.0 specific heat number. A 50/50 mix of ethylene glycol (the green stuff) has a tested specific heat number of 0.5 and of propylene glycol of 0.3. What this means is that it take twice the amount, in the case of the green stuff (and over three times for the red stuff) of BTUs to raise the same amount of water 1 degree!! This means that pure water will remove double the amount of heat and carry that heat away from the source per unit volume. Now, do the arithmetic and you will find out that the more pure water…the more heat gets taken away! Do not confuse this with the boiling point of the coolant. Pure water will boil at a lower temperature than that of a mix of water and antifreeze, as well as freeze at a higher point. The application of pressure in the system by the system through the normal expansion of water and gas during heating, is the solution to keeping the water from boiling away. A 10 LB pressure on water raises is vapor point to 239° F. I recommend a 25% mix of the green/red stuff to water for boiling protection, lubricating and corrosion resistance. Use only what you need!
- Use the highest tested pressure cap available, even though it only is actually a safety valve in your working system. Radiator caps serve no dynamic functional purpose other than to keep the coolant in under pressure when the natural expansion of liquids and gases takes place. Contrary to popular believe, the addition of a higher- pressure cap does not necessarily increase your systems likelihood of creating a leak due to pressure in the system. Always run a thermostat and if you hopefully have a high performance water pump make sure your thermostat has a by pass hole. By-pass types of thermostats are readily available from a variety of aftermarket vendors. If you already have a thermostat, then you can drill your own by-pass holes. If you remove the thermostat and run without it, it removes the “turnover” or turbulence (non-laminar flow) from the entrance to the radiator and will reduce the efficiency of the radiator. This turnover or turbulence is what makes sure that every molecule of water gets heated as evenly and fully as possible making for the best heat sponge. A good analogy is jumping in a lake and finding the surface water is warm to the touch, but a few feet down at your feet the water feels significantly cooler. This very same thing will happen in your cooling system if left to just laminar (smooth) flow and degrades the systems ability to carry and dissipate heat.
- With today’s high performance and high output engines, use a proven high flowing water pump. This is especially a wanted feature at idle and slow cruising speeds to speed the water flow through the radiator. Contrary to popular believe, slowing the water through the radiator does not improve heat dissipation! 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 carried and displaced. Stock pumps are okay generally for stock engines, but the high flow ones are a major step up.
- Do not use “under drive” pulley sets or kits! This equates to marketing fiction that you are going to save yourself bunches of horsepower by under driving your accessories. If you are on the racetrack and galloping along at 7000+RPMs, then you may save a few horses, but for street driven vehicles stock pulleys and now recently made available “overdrive” pulleys will spin your accessories over the stock levels that will help not only your cooling system, but your air-conditioning and electrical/power generation as well.
- Run manifold vacuum advance! This will aid low speed cooling situations. The correct application of vacuum advance mechanics will cause your engine to work more efficiently and therefore produce less heat at idle and slow speeds.
- For carbed engines…tune the carb. Don’t let a too lean condition spoil your idle or cruising down the road. In my experience, over 90% of the cooling issues with a car that makes to much heat on the move is the result of a too lean condition A too lean idle will also contribute significantly to produce more heat.
- Always use a quality fixed bladed mechanical fan with a clutch and shroud. They come as threesome in the deal for cooling. The absence of a shroud can cut CFM production in half. The use of flex fans on high performance engines are not the best design for the application. The incorporated use of a quality thermo-clutch is a must if you don’t want to fling that fan at warp like speeds…and give up to 40+ horses away.The use of electric fans is becoming more prolific in hotrods morphing from their popularity in modern day autos. These fans can be ever as bit reliable and actually can produce more CFMs at idle and slow speeds than that of any mechanical unit, making them excellent performers for heavy traffic and warmer climates. I highly recommend an electric booster fan for air conditioning when the compressor is running on mechanical fan equipped cars. This provides for additional heat removal, which the air system adds to the overall mix. Choose known quality electric fans and the measure of the fans ability to do work (or in this case move air in CFMs) by continuous watts or amperage. Watts or amperage are great yardsticks to figure if the fan is capable of moving the air it is claiming. Don’t fall prey to the “gorilla” type of electric fan ads that only have 12 or 13 amps of continuous operating current and advertise a whopping 2700 CFMs of production. Expect to pay at least a “C” note for a good one.
- Do not use metal coating(s) for your radiator hoses. This includes braided, sleeved or conical. The use of metal materials will actually act like an insulator and contain the heat to the system. Conversely…the use of bare aluminum/copper tubes in the system affixed with rubber fittings or ends will dissipate heat. If its rubber on the inside and metal on the outside it’s a no-no. If it’s rubber on the inside and outside or if it’s metal all the way through then it’s a yes-yes!
- Proper ventilation of the engine compartment is a must. Not so much as ambient temperature is concerned, but the free flow of air in the compartment to allow the free flow of air through the radiator. Simply, with pressure behind the radiator, it won’t accept cool air from the front…and thus no cool water in the radiator!
Simply put, the best cooling systems are the high five…high water content, high flow, high cooling surface areas, high turbulence and high CFMs.