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Coolant System Surge Tank Description
This surge tank is actually two chambers connected together, a surge tank and an overflow bottle. The top chamber is the surge
tank and is the highest point of the coolant system. It uses a threaded pressure cap, similar to the one used on a radiator or
engine fill system. The bottom chamber is the overflow bottle. This is the air space in the cooling system where the coolant can
expand into and contract from.
During vehicle use, the coolant heats and expands. The increased coolant volume can in some conditions push past the
pressure cap and through a channel into the overflow bottle. As the coolant circulates, air is allowed to bubble out. This air is
then transferred to the overflow bottle, through the surge tank cap, where it returns to the atmosphere. Under normal operating
conditions, no coolant is lost. Coolant without air bubbles absorbs heat much better than coolant with bubbles. When the engine
cools, the coolant, without air bubbles, contracts back into the surge tank from the bottom of the overflow bottle. The production
vehicle coolant bottle routing is shown below for reference. This surge tank is available from your authorized GM dealer and is
specific to the LTG engine.
Water Pump
The water pump is a centrifugal vane impeller type pump. The pump consists of a housing with coolant inlet and outlet passages
and an impeller. The impeller is a flat plate mounted on the pump shaft with a series of flat or curved blades or vanes. When the
impeller rotates, the coolant between the vanes is thrown outward by centrifugal force. The impeller shaft is supported by one
or more sealed bearings, which never need to be lubricated. With a sealed bearing, grease cannot leak out, and dirt and water
cannot get in.
The water pump circulates coolant throughout the cooling system. The pump is driven by the crankshaft from the drive belt.
Thermostat
The thermostat is a coolant flow control component, whose purpose is to regulate the operating temperature of the engine. The
thermostat utilizes a temperature sensitive wax-pellet element, which connects to a valve through a piston. Heating is causing
the element to expand and exert pressure against a rubber diaphragm. This pressure forces the valve to open. Cooling causes
the element to contract. This contraction allows a spring to push the valve closed.
When the coolant temperature is below 91°C (195°F), the thermostat valve remains closed. This prevents circulation of the
coolant to the radiator and allows the engine to warm up quickly. After the coolant temperature reaches 91°C (195°F), the
thermostat valve will open. The switch point will differ a little depending on engine. The coolant is then allowed to circulate
through the thermostat to the radiator where the engine heat is dissipated to the atmosphere. The thermostat also provides a
restriction in the cooling system, even after opening. This restriction creates a pressure difference which prevents cavitation at
the water pump and forces coolant to circulate through the engine block.
19328838
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LTG Crate Engine
IR 24OC14
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