THE CAVITATION

The manufacturer of diesel engines have increased the operation temperatures of their same engine, with the purpose of improving its efficiency. This means that the appropriate maintenance of the cooling system is particularly important. Overheating, excessive cooling,  punctures, erosion due to cavitation, the cracked cranks, jamming of the pistons, and the clogging of the radiator are typical symptoms of faults in the cooling system.
During operation, all of the internal combustion engines generate heat. The combustion temperature tends to reach around 1900º C. But only 33% of this total heat converts itself into a useful potential for the crankshaft. Approximately 30% is discharged with the exhaust gas, while the other 7% passes directly to the surface of the engine to the atmosphere. The remaining 30% is dissipated by the cooling system.

Corrosion is a chemical or electro chemical action that, with time wastes the metallic surfaces of a cooling system. In some cases, corrosion could destroy an engine. All of the components of the cooling system require protection against corrosion. Supplementary refrigeration additives are used to protect the metallic surfaces. The additives cover these surfaces and neutralize the contamination which is produced in the coolant. 
Amongst the different types of corrosion exists: erosion by cavitation and rust   pitting, inappropriate relationship between acidity/alkalinity and galvanic and electrolytic corrosion. Other functional effects are aeration and the formation of scale and deposits.

Erosion by cavitation and rust pitting:

The flow of electricity in a determined point causes pitting. The pits damage the components more than any other type of corrosion. When the pits begin to become deeper throughout a prolonged period, there is no practical manner of detaining them before they give way to perforations. As one sole amp of electricity which flows throughout thirty hours could eliminate 28 grams of steel, the flow of electricity which concentrates itself in a small area is very destructive. For this reason prevention is the best practice.
Erosion is a combination of mechanical and chemical and electrochemical action which produces corrosion. Cavitation is a particular type of corrosion and is, frequently, the cause of pits in the walls of the cylinders.

The cavitation of the wall of the cylinder is produced when air bubbles on its surface remove the oxide protection film. When the combustible mix explodes in the combustion chamber, the wall of the cylinder flexes itself and vibrates, which produces bubbles o fair in the coolant. The concentration of bubbles increase when the pressure is low in the cooling system or when it has leaks. Besides, upon the vibrations increasing, the quantity of air bubbles in the coolant also increases.

When the engine operates cold, the vibrations increase due to the fact of greater free space between the piston and the cylinder. The vibrations also increase when the engine is overcharged.
These bubbles are produced in the exterior wall of the cylinder (perpendicular in regards to the joint pin) and then explode towards the interior, or implode. When the air bubbles continue to experiment implosions, there is enough energy released to physically attack the wall of the cylinder and take out the oxide film, which produces corrosion and pits with a great deal of speed.
With time, a pit could become deep enough as to perforate the wall of the cylinder and allow coolant leaks within it. These leaks contaminate the lubricating oil.
The supplementary coolant additives cover the metallic surfaces and control erosion through cavitation and the  pits.
Unfortunately, small particles or iron scales often impede that the additive makes contact with the metallic surface. If this condition persists, pits could be produced. To avoid pits, keep the coolant system cool and regularly replace the coolant additives.

Inappropriate relationship of acidity/Alkalinity:

The content of acidity and alkalinity of one mix of coolant is measured according to its pH level. The pH level, which could vary between 1 and 14, indicates the grade of acidity or alkalinity and the grade of corrosiveness of the coolant. To reach better results, the level of the system should maintain itself between 8,5 and 10,5. When the pH level passes 11, the coolant attacks the aluminum and the cooper, or the non-ferrous materials. When the level is inferior to 7, the coolant becomes acidic and damages the ferrous materials. When the level is inferior to 7 or superior than 11, the coolant mix is not the proper one. The least corrosion is produced between 8,5 and 10.

The temperature affects the pH level.

At greater temperatures, the pH is, in general, lower.