Cavitation actually eats away the cylinder liners. "In a diesel engine, as the cylinder vibrates, it creates a momentary low pressure area in the liner," says Pressley. "The water then flashes to steam. The steam bubble smashes against the liner and literally erodes it away."
Conventional coolants use additives to protect against cavitation. "When you are using a diesel engine and you have a fully formulated coolant, it has nitrites and things to prevent cavitation," says Arcy. "As you accumulate hours or miles on the equipment, that level is going to go down. It could eventually go below the level where it is doing an effective job of protecting the cylinder liners."
Thus, you need to replenish conventional coolant additives on a periodic basis. But with ELCs, this interval is much longer, so there is less worry about missing maintenance.
As a result, extended-life or long-life coolants can actually help reduce the impact of poor maintenance practices. "If you don't have time to take care of your coolant, use something that is foolproof," Ulabarro advises.
The waterless alternative
Evans Coolant offers an alternative to water-based coolants that it touts as a life-long coolant. "We have a straight propylene glycol mixture," says Pressley. "When we eliminate the water, not only do we eliminate corrosion and cylinder liner cavitation, we raise the boiling point to almost 400° F."
Traditional water-based coolants rely on a pressure cap to raise the coolant boiling point to 250° to 255° F. Once you get above 180° F operating temperature, you only have about 70° before the coolant starts to boil.
"If you had a clear upper hose between the radiator and the engine block, you would see a frothy emulsion coming out because of all of the steam bubbles trapped in the coolant," says Pressley. "You begin to lose heat transfer."
As the temperature rises further, you get closer to the boiling point of the water. "As the temperature begins to increase to 220° or 230° F, you get steam pockets inside the cylinder heads due to the different characteristics of the water - surface tension, vapor pressure," Pressley notes. "As the incoming coolant comes by and there is no heat transfer, you get a hot spot. You can either develop detonation or, in severe cases, head gasket problems."
With the Evans Coolant, you are still 160° F below the boiling point when you are operating at 220° or 240° F. It is important to note here that all cooling fluids will boil in the cylinder head. "Your cylinder head can be 500° to 600° F," says Pressley.
What you want to prevent is steam pockets. "When Evans Coolant boils in the head, it automatically condenses when the incoming coolant comes in," Pressley explains.
Specific heat is one measure of a cooling fluid's efficiency that often gets attention. Water actually offers the best specific heat properties with a value of 1.0, according to Pressley. "A 50/50 glycol mix offers specific heat of .8, and we are down around .75," he notes. "But those properties only refer to when there is no boiling taking place - convective heat transfer where you have liquid all of the time."
Under light loads and low cylinder head temperatures, the 50/50 glycol mixes transfer heat better than the Evans Coolant. "In those scenarios, waterless coolant may run 5° or 10° warmer," says Pressley. But under such loads, it is really not an issue.
"Where we really shine is under heavy loads or ultra-high ambient temperatures when you drive engine temperature to 200° or 220° F," Pressley asserts.
The engine temperature gauge shows your average temperature, usually where the coolant is leaving the engine. "Inside the cylinders the temperatures are always much higher," says Pressley.
This is where Evans Coolant's high boiling point and molar heat of vaporization are an advantage, he claims. Molar heat of vaporization is really just how much heat it takes to make a liquid boil. As the coolant boils in the cylinder, the vapor bubble breaks away and is immediately replaced with incoming coolant. This helps to stabilize the temperatures.
Because of its high boiling point, the coolant also allows you to run a zero-pressure, open-vented cooling system; or you can choose to run the conventional closed system. Even then, there will not be as much pressure buildup in the system. "We only build up about 4 or 5 psi because the fluid expands 10% at 200° F and 15% at 250° F," Pressley points out.