07-6
RODIUS 2005.07
2110-01
ENGINE COOLING SYSTEM
2. DESCRIPTION AND OPERATION
1) GENERAL DESCRIPTION
The cooling system maintains the engine temperature at an efficient level during all engine
operating conditions. When the engine is cold, the cooling system cools the engine slowly o
r
not at all. This slow cooling of the engine allows the engine to warm up quickly.
The cooling system includes a radiator and recovery subsystem, cooling fans, a thermostat and
housing, a water pump, and a water pump drive belt. The timing belt drives the water pump.
All components must function properly for the cooling system to operation. The water pump
draws the coolant from the radiator. The coolant then circulates through water jackets in the
engine block, the intake manifold, and the cylinder head. When the coolant reaches the
operating
temperature of the thermostat, the thermostat opens. The coolant then goes back to the
radiator where it cools.
This system directs some coolant through the hoses to the heat core. This provides for heating
and defrosting. The coolant reservoir is connected to the radiator to recover the coolant
displaced by expansion from the high temperatures. The coolant reservoir maintains the correct
coolant level.
The cooling system for this vehicle has no radiator cap or filler neck. The coolant is added to
the cooling system through the coolant reservoir.
2) RADIATOR
This vehicle has a lightweight tube-and-fin aluminum radiator. Plastic tanks are mounted on the
upper and the lower sides of the radiator core.
On vehicles equipped with automatic transaxles, the transaxle fluid cooler lines run through the
radiator tank. A radiator drain plug is on this radiator.
To drain the cooling system, open the drain plug.
07-7
ENGINE COOLING SYSTEM
RODIUS 2005.07
2110-01
3) COOLANT RESERVOIR
The coolant reservoir is a transparent plastic reservoir, similar to the windshield washer
reservoir.
The coolant reservoir is connected to the radiator by a hose and to the engine cooling system
by another hose. As the vehicle is driven, the engine coolant heats and expands. The portion o
f
the engine coolant displaced by this expansion flows from the radiator and the engine into the
coolant reservoir. The air trapped in the radiator and the engine is degassed into the coolant
reservoir.
When the engine stops, the engine coolant cools and contracts. The displaced engine coolant
is then drawn back into the radiator and the engine. This keeps the radiator filled with the
coolant to the desired level at all times and increases the cooling efficiency.
Maintain the coolant level between the MIN and MAX marks on the coolant reservoir when the
system is cold.
4) THERMOSTAT
A wax pellet-type thermostat controls the flow of the engine coolant through the engine cooling
system. The thermostat is mounted in the thermostat housing to the front of the cylinder head.
The thermostat stops the flow of the engine coolant from the engine to the radiator to provide
faster warm-up, and to regulate the coolant temperature. The thermostat remains closed while
the engine coolant is cold, preventing circulation of the engine coolant through the radiator.
At
this point, the engine coolant is allowed to circulate only throughout the heater core to warm it
quickly and evenly.
As the engine warms, the thermostat opens. This allows the engine coolant to flow through the
radiator where the heat is dissipated. This opening and closing of the thermostat permits
enough engine coolant to enter the radiator to keep the engine within proper engine
temperature operating limits.
The wax pellet in the thermostat is hermetically sealed in a metal case. The wax element of the
thermostat expands when it is heated and contracts when it is cooled.
As the vehicle is driven and the engine warms, the engine coolant temperature increases.
When the engine coolant reaches a specified temperature, the wax pellet element in the
thermostat expands and exerts pressure against the metal case, forcing the valve open. This
allows the engine coolant to flow through the engine cooling system and cool the engine.
As the wax pellet cools, the contraction allows a spring to close the valve.
The thermostat begins to open at 82°C (180°F) and is fully open at 95°C (203°F). The
thermostat closes at 80°C (176°F).
