LO 11-6 Identify and describe the construction features, types, and applications of the diesel engine cooling components

1.4. Surge Tanks

Surge Tanks

Additional expansion volume for the cooling system is necessary to allow for the expansion of coolant. Surge or overflow tanks provide the space for coolant and vapor to move into when the engine coolant is hot. When the engine cools, the stored overflow volume returns to the radiator. Sometimes large radiator top tanks will accomplish the same purpose as a separate expansion reservoir. Overflow tanks use a line connected to the radiator just below the pressure cap, allowing coolant to move back and forth through the vacuum valve during the cooling system’s thermal cycles.

Surge and overflow tanks provide a coolant reserve for gradual loss of coolant. One study found that new trucks in their first year of service lost almost one gallon of coolant in the first year of operation—or about a drop of coolant per mile. Most of the leakage was determined to come from gear-type radiator hose clamps. Constant torque spring clamps are one of the best clamps to use to minimize coolant loss because they change dimensionally with the expansion and contraction of hoses and connections.

Vent Lines
Coolant vent lines located at the highest points on the engine and radiator bleed steam and air out of the engine and into the surge tank. If these gases are allowed to remain in the engine, they will accumulate in the cylinder head, EGR, or liquid air charge coolers, causing overheating. A water pump housing may even become air-bound, a condition where steam accumulates in the water pump housing and prevents coolant circulation.