Author’s note: In the Jan. ’09 issue of HPP, the technical article “Keep a Cool Head” described installing Evans NPG coolant in a Pontiac engine, along with other modifications. Due to the varied subject matter in that primer, HPP did not have the space to fully expose the theoretical aspect of heat transfer in a Pontiac engine and how that is altered with the Evans product. This primer picks up where we left off in 2009.

Many things have changed in the Pontiac world over the years. Components that were considered essential have been replaced with new technologies. The carburetor succumbed to the fuel injector; breaker points first to electronic ignition and eventually a system that has eliminated the distributor; and the simple throttle cable gave way to drive-by-wire technology. But little thought has been given to the heat transfer from the water jacket of the Pontiac cylinder head to the liquid coolant. This is what is required to keep an engine cool and detonation free, especially in a high-performance application or extreme use; that is until Evans Cooling Systems completely rethought the chemistry of cooling an engine.

Before this engine-coolant advanced concept that employs no water can be understood as it relates to a Pontiac, a review of cooling-system basics is in order.

Let It Boil (Almost)!

It is going to be hard for many Pontiac people to accept that fact that engine coolant on the verge of boiling is a good and proper thing. The caveat? It needs to occur in the cylinder head and not in the radiator.

The dreaded engine boil-over that strands you on the side of the road with the hood open and a cloud of steam emanating from the radiator is usually what comes to mind. That kind of boiling is not good.

When radiator boil-over occurs, it is rooted in the coolant becoming super heated and the radiator’s inability to transfer enough BTU of heat into the air. (This is known as rejection.) If this occurs, the coolant starts to boil and expand just as a pot of water would on a kitchen stove.

It is imperative to understand that the liquid’s job is to cool the engine, and the function of the radiator is to cool the liquid. As the liquid passes through the radiator, its temperature drops so that it can be an effective heat-absorption medium when it is pumped back through the engine. The liquid’s time in the radiator can be considered rest and relaxation as a soldier would receive between combat assignments.

If the liquid is not provided the opportunity to drop in temperature during its residence in the radiator, it then possesses too much heat to be effective. The liquid will keep absorbing heat from the engine until it can take no more. At that time, it boils and changes phase from a liquid to a gaseous form. The chemical composition of the liquid along with the operating pressure of the cooling system all impact the temperature at which the phase change occurs but cannot stop it. When the coolant boils and becomes a vapor, it is ineffective in pulling heat from the cylinder head.

The introduction of the radiator pressure cap by General Motors in the ’30s, along with the adoption of glycol-based coolants, were major advancements in raising the boiling temperature of coolant. As an aside, for every one pound of pressure that is added to a cooling system through a pressure cap, the boiling point increases 3 degrees F.

Environmental factors impact the boiling point of the coolant, also. Altitude has a major influence on lowering the boiling point of a liquid since there is less atmospheric pressure on it.

Misunderstanding the purpose of liquid coolant is rooted in the fact that the industry monitors the coolant temperature alone and not in conjunction with the metal-surface temperature of the combustion chamber in the cylinder head. Think of it as a mariner receiving directions in latitude without longitude. The proper method to determine if the engine is in thermal distress is to compare the liquid temperature to the metal-surface temperature of the cylinder head. Only then can the picture be clear. If the metal-surface temperature is climbing and the liquid reading is not keeping up, then the engine is on the verge of metal overheating though the coolant may be far from boiling.

As the liquid’s temperature increases its storage ability, its potential to absorb more heat is diminished. When this occurs, the liquid temperature as read on a coolant gauge may appear to be stable, albeit at an elevated temperature, but the metal-surface temperature of the combustion chamber and around the exhaust valve skyrockets. This can lead to detonation (ping) and engine failure from a cracked cylinder head.

Engines that employ an aluminum cylinder head are extremely sensitive to this since the steel valve seats are pressed into the head as an insert. Numerous or prolonged excursions to extreme metal temperatures along with thermal cycling can cause the seat to fall out. With rare exception, this is met with total destruction of the engine as the piston collides with the valve and the steel seat.

In almost every case, the engine never overheated according to the liquid temperature but the metal surfaces did. Thus, the most effective liquid coolant is one that has the ability to absorb a high amount of heat before boiling, which will result in the coolest metal temperatures in the cylinder head. When the liquid can abstain from boiling and continue to absorb heat there will be more thermal transfer from the cylinder head.

When discussing a cooling system it must be noted that though the coolant is also employed to remove heat from the engine block and cylinder walls, its most challenging assignment is to control the temperature of the combustion chamber and exhaust-valve area.

Different Levels of Boiling

The load and thus the heat rejection into the liquid coolant of an engine are not linear. It is dependent on many factors. Given a specific engine, the heat rejection required will depend on the operating state of the vehicle.

A Pontiac that is used for light-load driving (even if it is a great distance) will not put much heat into the coolant. This is due to the engine not being required to produce much power for the driving state. The amount of fuel consumed and the volumetric efficiency of the cylinder bore are low. If the same Pontiac is now required to climb a steep hill or pull a trailer, then the load on the liquid coolant increases dramatically. This is the reason that since the days of the early automobile, car companies have performed hot-weather testing in the American west where a combination of high ambient temperatures and extreme elevation can be found at the same time.

Turbulent flow through the cooling system is necessary for the most effective thermal transfer. This action will cause a churning and allow the coolant to absorb more heat from the components it comes in contact with.

In like fashion it is imperative that the cooling system is devoid of any air bubbles and is a solid stream of liquid. Air is a very poor heat-transfer agent when compared to a liquid. If the cooling system is air bound then the areas that do not have liquid contacting them very quickly become superheated, and that will result in extreme thermal stress.

The liquid coolant goes through a number of defined boiling stages as it absorbs heat and prior to becoming steam. These range from nucleate boiling to crisis boiling. When the liquid is just on the verge of entering the nucleate stage is when the most heat transfer occurs. When crisis boiling occurs, the liquid for all intents and purposes does little to cool the cylinder head and the metal-surface temperature rises rapidly.