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by Butch Thomas  More from Author

Understanding and Installing Evans Coolant

Evans Cooling Systems Inc. has developed an antifreeze called NPG+ and NPG-R (nonaqueous propylene glycol) that use no water, never freezes and does not boil until 375 degrees F. Though it has been on the market for a few years, most enthusiasts do not know about it. Those that are familiar with the name often do not fully grasp its attributes. The problem is, you need to be intimate with how an engine’s cooling system and the liquid coolant itself functions to recognize the benefits of the chemistry.

The temperature gauge reads the heat in the liquid coolant, and not the metal surface temperature of the cylinder head. Detonation, run-on and sluggish performance are often blamed on today’s gasoline and the amount of compression in an engine. Though these are factors that impact the way an older or even a new engine runs, the effectiveness of the coolant is more paramount to the state of tune than acknowledged. All too many collector and muscle cars have the ignition advance curve dialed back to eliminate detonation, when the real culprit is excessive combustion chamber surface temperature from an ineffective cooling system. The gauge reads fine, but the cylinder head is superheated. Even the most efficient water pump and radiator are limited in their performance with traditional coolants. The chemical composition of the water and anti-freeze mix is limited by design. Conventional coolants do a great job for what they cost, but in most applications allow a great deal of power to be left on the table – the engine tune-up is altered to work under the amount of heat removed from the cylinder head. This is a theory that even the most ardent engine builder and enthusiast often overlooks.

Unlike most magazine technical articles, this primer is more about understanding than doing. The coolant itself is a simple pour-in once all the old water based antifreeze is removed. The chemistry in the Evans products will do the rest. So before we introduce the steps for a proper conversion, a brief overview of coolant and how it functions will be addressed.



The primary purpose of a liquid coolant is to remove heat from the cylinder head and engine block. Secondary concerns all apply to how the coolant transfers heat, its ability to be pumped, limit corrosion and deposits, offer lubricity, and not freeze.

Traditional anti-freeze is a 50/50 mix of ethylene glycol and water that is often abbreviated as EG.

Heat is transferred from the cylinder bore and cylinder head to the liquid coolant. The state of the coolant is dependent on the rate of heat input. When the coolant reaches the hottest part of the cylinder head, which is usually around the combustion chamber and exhaust valve, it will actually start to boil. This phase change is identified as nucleate boiling and allows efficient transfer of heat. The coolant’s chemical and thermal reaction is responsible for how efficient this process becomes. 

At very low load on the engine, no boiling occurs. During higher engine loads and speeds, the rate of heat flow through the cylinder head is increased until steam bubbles are formed in certain regions on the surface of the water jacket. These areas are the metal bridge between the exhaust valve seats and spark plug boss.

Under severe engine load and speed, the vapor bubbles become so large and numerous that the liquid has difficulty flowing. When this critical temperature is reached, the hot surface of the water jacket suddenly becomes insulated by individual steam bubbles which join together to form a film. Under these conditions the film insulates the water jacket from the coolant, and metal surface temperature of the cylinder head elevates dramatically and can cause the engine to ping or lack power – even though the temperature gauge shows no sign of this condition!

The boiling point of a liquid is defined as the temperature at which the vapor pressure is equal to the external pressure on the surface of the liquid. Back in the early days it was common for engines to “boil over” when carrying a heavy load in high elevations, like those found in the mountains of the western United States. These early cooling systems were not pressurized, so increases in altitude were very problematic.



When it comes to boiling it is true that it is not desirable to have this occur in the radiator. The radiator’s job is to cool the liquid, while the liquid’s task is to cool the engine. If the radiator of an engine is boiling over, it means the coolant is becoming superheated and turning to a vapor. When it re-condensed it contained too much heat for the radiator to dissipate. So as you can see, we need to identify where it is good and sound engineering to have the coolant boil.

Before this topic can be explored, it needs to be recognized that the load on the cooling system and the coolant itself is not the same under all driving conditions. At idle and light load such as cruising down an interstate highway, the engine is not required to produce much power. The amount of power required to move a vehicle at 65 mph is only a fraction of what the engine can produce at maximum output. On average, an older car only requires 25 to 30 horsepower to cruise on level ground at 65 mph. Since an internal combustion engine is nothing more than a heat pump, the thermal load the liquid coolant and the radiator is exposed to is proportional to the heat of the power produced. If the same vehicle is asked to climb a long grade at a steep angle, pull a trailer, or produce maximum power for passing or racing, then the load on the coolant and radiator increases.

A coolant must work to meet the transient needs of the engine. Many falsely believe that water is the best coolant. That would be true if the engine was going to do nothing but idle, or never produce anywhere near maximum power during its lifetime. With its specific heat rating and good thermal conductivity qualities, water does an excellent job of cooling an engine – that is, until the load is increased and the coolant starts to boil in the cylinder head. Never mind the fact that water creates rust and corrosion that insulates the liquid from the water passages, diminishing thermal transfer in the engine and radiator. When this happens in the engine, the water would stay cooler since there is less heat rejected into it but the metal surface temperature of the cylinder head would be much higher. In addition, water offers no lubrication properties for the pumping mechanism (water pump) and will freeze.

As the coolant is asked to work harder, boiling occurs in the cylinder head water jacket. Thus, EG antifreeze can actually wear out. This is a result of the additive package becoming neutralized and consumed from the high temperatures and constant phase change that is occurring. An engine that is loafing for most of its life and hardly ever has the coolant work hard will have the additives stay active longer. For this reason, if traditional EG-based coolants are used, they need to be changed on a regular basis. The recommendation of a maximum of three years is only for an engine that sees normal duty. In severe usage such as racing or towing, the coolant would need to be changed much more frequently.

Evans NPG+ is a lifetime coolant. It has lower surface friction than EG/water, and boils at 375 degrees F at atmospheric pressure. This allows the coolant to remove more heat from the cylinder head and limit heat-related detonation. It also eliminates all water along with the possibility of corrosion or cylinder liner cavitation in wet sleeved race engines such as the big-bore LS series. Collector cars that are hardly used will benefit from the lack of corrosion from the absence of water with the Evans product.

The boiling point of a coolant increases 3 degrees F for every pound of pressure created by the radiator cap. A common 15-psi cap will have water boil at 257 degrees F. Water/EG will boil at 264 degrees F at 15 psi, giving the Evans product an advantage of 105 degrees F. When choosing a coolant for an engine, you need to consider the worst-case conditions, not idle or light load. Traditional coolants are inferior when the load or horsepower increases. That is where the Evans product shines, allowing for better protection and a more aggressive tune-up.

To install the Evans coolant in any engine, all of the old coolant needs to be removed since any water-based product will impact its effectiveness.

The company offers two products: NPG+ and NPG-R, along with a Prep Fluid to help remove the old coolant if the block drains cannot be accessed. NPG-R is the best choice for a racing application that must meet a requirement of a sanctioning body in regard to engine coolants, but is not considered a lifetime product. The NPG+ can be used in almost every application, and does not require any special radiator or water pump. Its viscosity is very near traditional coolant; the NPG-R is even thinner than NPG+.

For our installation we worked with IDA Automotive in New Jersey, as Bob Ida switched his street/road race 2010 Corvette Grand Sport to the Evans NPG-R. Bob has done countless installations of Evans coolant in all types of vehicles – blown street rods to his land speed record-holding race truck, and everything in between. Regardless of the use, Bob told us that he has never had a time when the coolant did not either fix an overheating issue, or not allow a more aggressive engine calibration. An additional benefit of the Evans product is that it builds much less pressure in the cooling system, even with a stock radiator cap. Its rate of expansion is lower than EG. This means all of the parts exposed to the coolant will enjoy a longer life, since they are not stressed as much.

It is hard to believe that a coolant can have so much effect on an engine. As the author I write this with experience. My three vehicles and farm tractor have all had Evans NPG+ in them for the last six years. I will never go back to conventional coolant. The trick is to do a proper installation and get beyond the obstacle of the cost (around $40/gallon). Just ask Bob Ida, he says it’s the best money he has ever spent under the hood of a car!




Bob Ida road races his modified C6, and knows from experience the benefit of the Evans NPG coolant’s higher boiling point and reduced cylinder head metal surface temperature. He told us that on the hottest of days, he can lap the car with no perceptible decrease in performance – unlike standard coolant.


Ida has extensive dyno experience and usually takes advantage of the Evans coolant with a more aggressive tune-up, but that is not required. No tuning is necessary to enjoy the benefits of NPG.


The C6 Corvette has a very efficient cylinder head design that makes it less prone to detonation. Older engine styles or those with forced induction have the potential to see huge gains from the Evans NPG line.


We installed the NPG-R in the Corvette since it is accepted by the racing associations. A better choice for most street or collector cars would be the NPG+ for its longer service life.


The process begins by draining the radiator and accessing the block drains to remove all of the old coolant. Here Bob is removing a block drain from the LS3. If possible, remove the heater hoses and use compressed air to blow out the old coolant.


Due to the level of preparation, the next step was to fill it with the NPG-R and run the engine. Most will choose to not remove the block drains and use the Evans Prep Fluid to pull out the old coolant. Install two gallons of Prep Fluid and run the engine with the heater on until it is fully warm and the thermostat is open. Drain the Prep Fluid. It can be saved for another installation. The method to confirm the amount of moisture is to use a special refractometer from Evans ($69.95).


A sample of the coolant or Prep Fluid is placed on the sight glass of the refractometer. The instrument provides a scale in a value called Brix.


With the sample on the sight glass, the instrument is looked through and a scale read. It is supplied with a chart to identify the amount of water left in the system as a percentage.


The ideal is to have 0% water, but that is hard to accomplish with an in-service conversion. A good reading is no more than 5%. As the vehicle is used, the remaining moisture will boil off. If the value is above the desired percentage, simply drain out a gallon of the coolant and replace it with another fresh gallon. The drained coolant can be heated in a pot on a barbecue grill to boil off the water it absorbed, and then used in the vehicle at a later date.


(Photo courtesy of Evans)

At press time, the NPG+ and NPG-R retail for $39.95/gallon, the Prep Fluid is $33.95/gallon, and the refractometer is $69.95. The average conversion cost for an in-service engine is around $200. If a new engine is being built, all that is required is to blow out the heater core and pour the Evans coolant in the radiator.





Evans Cooling Systems, Inc.

255 Gay Street

Sharon, CT 06069



IDA Automotive Inc.

600 Texas Road

Morganville, NJ 07751



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