1. Purposes and Functions of the Cooling System

1.11. Minimizing Engine Corrosion

LO 11-02: Identify and explain the purposes and functions of the cooling system.

 

Minimizing Engine Corrosion

Dissimilar metals in contact with engine coolant cause electrochemical reactions Figure 16. The coolant is an electrolyte, which means it can conduct electrical current. In a sense, the cooling system can behave like a primary battery in which dissimilar metals in the presence of an electrolyte produce a flow of electric current. This principle of inducing current flow by using dissimilar metals and an electrolyte is called the galvanic effect . Unless some strategy is used to prevent these reactions, some of the metals in contact with the coolant will become severely corroded through these chemical reactions. For this reason, antifreeze contains a number of additives that minimize electrochemical reactions, prolonging the durability of engine and cooling system components. It also explains why it is important to clean and properly maintain the multiple engine electrical wiring grounds, especially those dedicated for the starting motor and alternator. Engine coolant should never be allowed to become a ground pathway for damaging electrical current. Instead, lower-resistance cable grounds should conduct current flow.

   Fig11_16

FIGURE 11-16: This injector tube, which is surrounded by coolant, transfers heat away from the injector. The brass in tubes like this—along with other metals, such as aluminum and iron in the cooling system—produces galvanic electrochemical reactions that lead to corrosion.

 

  Technicians Tip  
  Galvanic activity in a cooling system is easily measured with a digital multimeter. After setting the meter to a low-voltage, direct current (DC) scale, place one lead in the coolant. Place the other test lead anywhere on the engine where there is metal exposed for a good ground connection. A cooling system with a level of additives that is adequate to protect metals from corrosion tests at 0.2 volts or less. Coolant that has become depleted of additives or highly acidic or alkaline (basic) will produce more voltage. If the voltage exceeds 2 volts, the cooling system should be drained and flushed and new coolant containing the recommended level of corrosion-inhibiting conditioners should be added.  

 

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