LO 11-2 Identify and explain the purposes and functions of the cooling system

1.10. Deaeration of Coolant

Deaeration of Coolant

Aeration is the condition in which excessive amounts of air or steam bubbles are dissolved in coolant, which reduces the coolant’s effectiveness. Cooling systems must provide for deaeration of the coolant to prevent pumps and coolant passageways in the cylinder head from becoming air-bound or blocked by an accumulation of vapor or steam Figure 14. As coolant warms, some vaporization occurs, forming bubbles and vapor pockets. Even when coolant is relatively cold, coolant next to hot internal engine surfaces becomes hotter than surrounding coolant and vaporizes. If the vapor collects into large steam pockets, the engine cannot transfer heat to the coolant, causing localized hot spots and potential damage from overheating Figure 15. Additives called wetting agents are sometimes added to the cooling system as a chemical supplement or as part of the additive package in antifreeze. Wetting agents are essentially chemicals that reduce the surface tension of bubbles, which causes them to quickly collapse as they grow.

FIGURE 11-14: Vent lines from the engine block and the radiator connect to the deaeration tank, also referred to as the surge tank . Without deaeration, the engine coolant flow becomes blocked.

FIGURE 11-15: Two surge tanks that deaerate coolant are used by this prototype Freightliner eM2 chassis. It is critical that vapor is removed from coolant that circulates through the electric motors, batteries, and power electronics.