The ideal is to be less than...
The ideal is to be less than 5 percent water on a refill such as ours. The GTO tested at 4 percent. At the time of publishing the prices were: Prep Fluid, $27.75/gallon; NPG+, $32.50/gallon; water pump, $189.95; thermostat, $9.95.
When water is employed as a coolant-a use that is common with competition and especially drag-race engines-the flow is usually restricted; the theory being, "slow the water down so that it has time to cool off in the radiator." This is an inaccurate response to the use of a poor coolant. To limit boilover, the higher pressure is required to raise the vapor point of the water to try to keep the cylinder head cool. When a restrictor is placed in the flow path, the system pressure increases and thus, the boiling point. In tests conducted by independent sources, some race engines had pressures as high as 60 psi or greater in the rear of the cylinder head because of the use of a flow restrictor. The engine builders thought they were controlling heat by reducing flow, but in actuality were creating such a high pressure to make up for the deficiencies of water as a coolant, even when treated with chemicals that are supposed to enhance its ability.
What is usually not taken into consideration is the added horsepower required to drive the water against 60 psi of pressure that the restrictor creates. These are all Band-Aid efforts to make up for the poor qualities of water as a coolant in anything other than an engine that is going to idle and produce only a minimum amount of its rated maximum power.
It is advantageous for the coolant to boil in the cylinder head, but it needs to refrain from undergoing a phase change for as long as possible for it to be the most effective. Then, it must release easily so it can move from that spot and take heat with it. Next, it's required to recondense quickly and be pumped with ease. Once it enters the radiator, it must possess enough thermal dissipation to drop in temperature and be ready for the entire event again.
As the coolant is asked to work harder, boiling occurs in the cylinder-head water jacket. Thus, the 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 and renewed 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+ has a lower surface tension than EG/water, boils at 375 degrees F at atmospheric pressure allowing the coolant to remove more heat from the cylinder head, and eliminates all water and the possibility of corrosion, along with cylinder liner cavitation in wet-sleeved race engines such as the big bore LS series.
Even with a 15 psi pressure cap, water boils at 257 degrees F(water/antifreeze boils at 264 degrees F at 15 psi) giving the Evans product an advantage of 105 degrees. When choosing a coolant for a high-performance Pontiac engine, you need to consider the worst-case conditions, not idle or light load. Traditional coolants are inferior when the load/horsepower increases.
System Approach
Though the Evans NPG+ can be installed in any Pontiac engine (stock or modified) with excellent results, our subject vehicle with 560 hp was an extreme example of a street car.
Evans Cooling Systems offers a complete cooling system package for Pontiac engines. It features a high-efficiency water pump with a scroll-style impeller and bleed orifice along with a high flow Robertshaw thermostat.
Conclusion
With the complete Evans system installed, the subject GTO now runs 192 degrees F on the highway during summer weather. While sitting in traffic, the temperature never goes above 210 degrees F and, more important, since the coolant is removing the heat from the engine, it runs great at any temperature. The loading up and poor drivability after elevated coolant temperature is now gone. Doug said that previously he would open the hood after a 25-mile run and it would feel like a blast furnace. With the Evans system, he told HPP that it stays much cooler under the hood.
The important thing to note is that though the liquid temperature on the gauge hasn't changed much aside from when the pulley was swapped for a smaller one, the cylinder-head metal surface temperature has dropped dramatically with the Evans NPG+. This proves the temperature-gauge reading is only part of the story when it comes to engine heat.
Now that the heat is under control, the next step is to put the Pontiac on the shop's chassis dyno, and recurve the distributor and lean the carburetor to take advantage of the cooler combustion chambers.
If you would never believe that a simple coolant swap would completely change how an engine runs, think again. With the Evans NPG+ this 560hp GTO runs as well on a 90-degree day as it did before in 60-degree weather. The key is keeping a cool head!