The Boiling Regimen
When it comes to boiling, it's true that it's 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, the coolant is becoming super heated and starts turning into vapor. When it recondenses, it contains too much heat for the radiator to dissipate. So, as you can see, we need to identify when and where it's good to have the coolant boil.
The load on the cooling system and the coolant itself isn't the same under all driving conditions. At idle and light load, such as cruising on the highway, the engine isn't required to produce much power. Since a diesel engine is nothing more than a heat pump, the thermal load the liquid coolant is exposed to is proportional to the heat of the power produced. When climbing a long grade, pulling a trailer, or producing maximum power, the load on the coolant increases. The coolant must work to meet the transient needs of the engine.
Traditional antifreeze that's a mix of EG and water solves some of the problems but brings along its own set of issues. Water by itself has a very high surface tension, and when it does boil it's hard for it to release and recondense back to a liquid and remove heat from the boiling-point location. In simple terms, it's 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. Then it's required to recondense quickly.
Once it enters the radiator, it must possess enough thermal dissipation to cool and be ready for the entire event again. 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. This is not to be confused with the freeze point. That doesn't change as the additives are depleted. 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 more frequently.
Evans Cooling Systems has developed its NPG+ coolant that has a lower surface tension than EG/water, boils at 369 degrees at atmospheric pressure, and allows the coolant to remove more heat from the cylinder head. It also eliminates all water and the possibility of corrosion and cylinder liner cavitation. In addition, it's a lifetime coolant that will perform for 300,000 miles with no need to introduce any SCA.
Even with a 15-psi pressure cap, water will boil at 257 degrees (water/EG will boil at 264 degrees at 15 psi), giving the Evans product an advantage of 105 degrees. When choosing a coolant for a diesel engine you need to consider the worst-case conditions, not idle or light load. Current EG/water mixes, though the standard, are inferior when the load/horsepower of the engine increases.
 Coolant test strips should...  Coolant test strips should be used to determine if the level of additives are sufficient to suppress liner cavitation on Ford diesel engines. |  Dominick Improta of Speedway...  Dominick Improta of Speedway Performance converts many diesels to the Evans coolant. |  When switching to the Evans...  When switching to the Evans NPG+, all of the old coolant must be drained. The level of water in the system is checked with a refractometer. Here, a sample is being taken on a test stick. |