Story & Photos By John Oates

Evans Cooling Systems, located in the sleepy little town of Sharon, Conn., has been working with cooling systems and cooling technology for over 20 years. They’ve worked with Trans-AM GT-1 race cars, oiling systems, and developed the reverse cooling system used in the production Corvette.  These developments made an impact on the racing scene, but perhaps none more than their newest technology. In this series of stories, we’ll start with a discussion of their technology and why it works.

The second article will deal with the race teams who have used it and can relate the benefits to their program. Hopefully, you will gradually begin to dispose of your previous thoughts about cooling systems. The Evans system does not require high pressure water pumps, antifreeze or Ethylene Glycol and water (EGW), high pressure radiator caps, flow restriction, or even water.

What ? Not even water ? Yes ! The cornerstone of the Evans system is the replacement of the water with a liquid called Evans NPG coolant. Before we get to that point, though, you need to understand what is going on inside the engine.

Most engines can run more efficiently than they do. Higher compression rates are one way to produce more power. Unfortunately, trying to wring every bit of horsepower out of an engine creates more heat. The more heat created, the more the coolant vaporizes trying to absorb the heat. As this happens, the coolant loses some of its ability to absorb heat from that particular area of the combustion chamber. The Evans system is designed to respond to those hot spots in the engine.

It is important to understand what goes on inside the engine, and to differentiate between liquid temperature and metal or component temperature. There is a phenomenon in all coolant systems called nucleate boiling. Nucleate boiling takes place when liquid coolant comes in direct contact with the hot metal of the cylinder head or block, which has reached or exceeded the boiling point of the coolant. Under a condition like this, the liquid turns to vapor at the hot surface. This is similar to dropping some water onto an already-heated cast iron skillet. Some of the water is turned immediately to steam, and some sits there and sizzles. The change in state from liquid to gas (vapor) absorbs a great deal of heat. Eventually, the vapor will break away and be replaced by additional liquid coolant. A substantial quantity of heat is absorbed into this layer of liquid coolant from the metal surfaces of the engine, yet those surface temperatures of the metal never rise above the boiling point of the coolant.

Nucleate boiling is eliminated when the coolant itself is continuously displaced from the surface it is trying to cool by a thin layer of vapor. This thin layer of vapor is called “film blanketing". Returning to our skillet scenario, when the water hits the surface, it boils almost immediately. This is a form of nucleate boiling and it dissipates heat. As this continues, a small film of vapor can form right on the surface of the skillet, separating the liquid from the hot surface. This is film blanketing. As this occurs, the metal surface becomes insulated from the liquid and continues to heat. When this begins in one area, unless the vapor blanketing process is stopped, it will spread and continue to heat adjacent areas. This does not stop until the area is cooled down and the vapor condenses back to liquid. Obviously, the only way for the heating to go away is if the engine is turned off and allowed to sit, not a practical solution for a racing engine.

After determining that nucleate boiling was good and vapor blanketing was bad, Jack Evans set out to find a way to maximize the nucleate boiling. Evans’ NPG coolant is a Non-Aqueous propylene glycol. Their form of propylene glycol is a stable, non-hazardous, non-toxic, non-corrosive liquid. It s even used as a food additive in some popular beverages. The NPG coolant maintains a vapor-free liquid-to-metal contact. (If you pour the NPG into the aforementioned skillet, it will boil, but would not form the vapor blanket that plain water, or even EGW does)
 

Evans Cooling has a spotless facility.

Since we determined that boiling was good, but blanketing was bad, you would imagine NPG would have a lower boiling point than water. Actually, it is just the opposite. But, taken in total, the characteristics of NPG work more efficiently than plain water or EGW. Evans’ NPG has a higher boiling point than water. Water boils at 212 degrees Fahrenheit, NPG at 369 degrees. The NPG is a more viscous liquid, especially at cooler temperatures. NPG has a higher latent heat of vaporization, or the amount of heat necessary to turn it into steam. It also has less surface tension than water, meaning it will flow and won’t adhere to a surface. I know it doesn’t make sense to have a liquid that is thicker than water, but actually flows better, but it does. In summary, it is thicker than water, uses up more heat to turn to vapor than water, has less surface tension, and has a higher boiling point.

In order to make the NPG work similar to water and to overcome a slight imbalance in the heat transfer characteristics, Evans Engineering needed to create a system that caused the liquid to flow at a greater rate. The heat transfer of the NPG is about ½ of EGW. To maximize the benefits of the NPG, the flow rate of liquid passing through the engine, needs to be doubled. In order to achieve this increased flow, some changes had to made. This is where you begin to lose the restrictions built into most cooling systems.
 
 

On the bottom, a stock water pump; on the top the Evans pump. Notice the large discharge tube, and the larger casting for the pump impeller.

The standard water pump impeller, the part that throws the water around, is not capable of producing the necessary flow. Attempts were made to spin the pump faster, but that resulted in cavitation or the impeller trying to pump more than the supply could provide. They also experienced problems with bearings, the impeller shaft coming apart and even pump casings cracking under the increased strain. So, Evans decided to cast their own pump. When they made it stronger, they also made it better. Through an arrangement with a Cleveland, Ohio foundry, Evans produces water pumps entirely of their own design. They currently have pumps for the big and small block Chevy, with others under development. The NPG pump has increased inlet and outlet diameter for greater flow. The impeller is of their own design, and can flow a higher capacity. There is also an air bleed at the top of the pump to remove any air remaining after the system is filled.

Once they achieved the flow they needed from the water pump, their next concern was the radiator. Griffin Radiator has taken the Evans design and now produces a radiator that can flow the rate the NPG system requires. Using tubes of 1.25 or 1.5 size, the flow is increased across the radiator, giving the liquid greater contact with the tube, the tube more contact with the air. The fin density is also changed. The proper amount of fins leads to greater efficiency - less fins = less air drag. Their radiators also use a zero pressure cap. Because of the increased flow rate of the pump and the properties of the NPG, there is no need to pressurize the system. Standard water systems were pressurized to create a higher boiling point for the water or EGW. Because the NPG already has a higher boiling point, the pressure is not necessary. Running the coolant system at low or no pressure creates a safer system.

After years of research and development by Evans Engineering, the racer can have a balanced, thoroughly designed system. Prior to the introduction of NPG, many of the changes to standard water systems were add-ons in response to overheating problems. With the NPG, you have a complete engineered system. The system uses no water, no anti-freeze. The water pump is designed specifically for this purpose and is stronger and more capable than most aftermarket pumps. The radiator is designed to work hand in hand with the other two components, providing a complete cooling system.

Evans Engineering has spent many years and countless hours on the dyno and at the track making this system work. You have the opportunity to add that result to your race car. If you still don’t believe, though, in the second half, we’ll talk to some of the folks who have used Evans NPG.
 

NOTE: The author wishes to thank Steve Pressly, Jack Evans, and Rick Bell from Evans Cooling for taking the time out of their day(s) to help me understand how good this stuff is.