The Evans NPG+ is a gold color...
The Evans NPG+ is a gold color when new but over time will become very dark. When this happens, there is nothing wrong. All of the dyes used for antifreeze are water-based ,and since the system is non-aqueous, the dye dissipates.
Vapor Pressure And Boiling Point
All liquids create vapors. The amount of vapor produced is defined by the chemical characteristics of the liquid. Pressure exerted by these vapors in the presence of the liquid is defined as vapor pressure, which increases as the temperature is elevated.
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. When a liquid is heated in an open vessel, it will boil when its vapor pressure is equal to the atmospheric pressure.
Keeping this in mind, as elevation is increased the atmospheric pressure decreases, and thus, the boiling point of a liquid is lower. Back in the early days, it was common for the 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.
Glycols have lower vapor pressures than water and their boiling points are higher. If external pressure is reduced, the boiling point of the glycols will also be reduced but will still be higher than water. Thus, glycols are considered high-boiling-point liquids because of their low vapor pressure compared to that of water at a given temperature. As an example, at 68 degrees F the vapor pressure of water is more than 100 times greater than that of some glycols. The low volatility of glycols lessens their tendency to evaporate and has led to their use as antifreeze for engines.
Mixes of glycol and water generally have physical properties between those of water and anhydrous glycols. Adding water lowers its boiling point over that of straight glycol. The smaller the concentrate, the lower the boiling point will be.
Glycols are usually more fluid than many of the other high-boiling-point chemicals. For this reason, they work well when mixed with water to create a viscosity that can be pumped easily when cold through an engine, radiator and heater core.
We used a Lisle Radiator Fill...
We used a Lisle Radiator Fill Kit to help bleed the cooling system. This is a great tool that belongs in every hobbyist's garage. It allows the cooling system to be filled and bled without spitting any coolant on the ground.
Freeze Point
When liquids are cooled, they eventually either crystallize like ice or become increasingly viscous (thicker) until they fail to flow and set up like glass. Crystallization represents true freezing that is seen with water, while a change into a glass-like substance is called supercooling.
Glycols do not have sharp freezing points. Under normal conditions, straight glycol would supercool rather than freeze.
Specific Heat
Specific heat is defined in the McGraw-Hill Dictionary of Engineering as: "The ratio of the amount of heat required to raise a mass of material one degree in temperature to the amount of heat required to raise an equal mass of a reference substance, usually water, 1 degree in temperature. Both measurements are made at a reference temperature usually at a constant pressure or constant volume."
In simpler terms, specific heat can be considered the ability of the liquid to store heat. The specific heat of water is approximately 1 at ordinary temperatures. Specific heat varies with temperature, so a value for a reference needs to be assigned.
The specific heats of glycol mixes are higher than straight glycols. This is important when engine coolants are used as antifreeze. A liquid with a high specific heat will do more work per unit weight than one with a low specific heat, if all other factors are equal.
Surface Tension
Surface tension is the force on the surface of a liquid, which tends to diminish the surface area to a minimum. The surface tensions of glycols are less than that of water. Generally, when heat is applied to a liquid, the surface tension is reduced. In the case of glycols, heat does not affect the surface tension materially, except when the temperature is near the boiling point.