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

1.6. Coolant Expansion in Cooling Systems

Coolant Expansion in Cooling Systems

Cooling systems must provide for the expansion of liquid coolant. As engine coolant warms, it expands to occupy a larger volume. An overflow reservoir is needed to contain hot coolant that is pushed out of the radiator and engine during warm-up. Surge tanks, overflow reservoirs, and large radiator top tanks are used to buffer coolant expansion Figure 11. Some coolants are made with propylene glycol, which is nontoxic and environmentally friendly; however, most antifreezes are made from a base chemical called ethylene glycol, which is considered toxic and must not be allowed to escape into the environment through overflow hoses. When the engine cools, coolant is drawn back into the radiator through negative pressure caused by the contraction of cooling coolant in the closed cooling system Figure 12.

FIGURE 11-11: The surge tank and overflow reservoir are contained in a single unit.

FIGURE 11-12: When coolant is heated, it expands. The overflow reservoir or surge tank collects coolant leaving the cooling system through the overflow pipe below the neck of the radiator cap. After the engine cools, coolant is drawn back into the cooling system.