open gas tank LAND ROVER DEFENDER 1999 Workshop Manual

26COOLING SYSTEM
6
DESCRIPTION AND OPERATION By-pass flow valve
The by-pass flow valve is held closed by a light spring. It operates to further aid heater warm-up. When the main
valve is closed and the engine speed is below 1500 rev/min, the coolant pump does not produce sufficient flow
and pressure to open the valve. In this condition the valve prevents coolant circulating through the by-pass circuit
and forces the coolant through the heater matrix only. This provides a higher flow of warm coolant through the
heater matrix to improve passenger comfort in cold conditions.
When the engine speed increases above 1500 rev/min the coolant pump produces a greater flow and pressure
than the heater circuit can take. The pressure acts on the flow valve and overcomes the valve spring pressure,
opening the valve and limiting the pressure in the heater circuit. The valve modulates to provide maximum coolant
flow through the heater matrix and yet allowing excess coolant to flow into the by-pass circuit to provide the
engines cooling needs at higher engine rev/min.
Outlet Housing
A cast aluminium outlet housing is attached to the cylinder head with three bolts and sealed with a gasket. Coolant
leaves the engine through the outlet housing and is directed through a hose to the heater matrix, the radiator or
the by-pass circuit.
An Engine Coolant Temperature (ECT) sensor is installed in a threaded port on the side of the outlet housing. The
sensor monitors coolant temperature emerging from the engine and sends signals to the Engine Control Module
(ECM) for engine management and temperature gauge operation.
Expansion Tank
The expansion tank is located in the engine compartment. The tank is made from moulded plastic and attached to
brackets on the right hand inner wing. A maximum coolant when cold level is moulded onto the tank.
Excess coolant created by heat expansion is returned to the expansion tank from the radiator bleed pipe at the top
of the radiator. An outlet pipe is connected into the coolant pump feed hose and replaces the coolant displaced by
heat expansion into the system when the engine is cool.
The expansion tank is fitted with a sealed pressure cap. The cap contains a pressure relief valve which opens to
allow excessive pressure and coolant to vent through the overflow pipe. The relief valve is open at a pressure of
1.4 bar (20 lbf.in) and above.
Heater Matrix
The heater matrix is fitted in the heater assembly inside the passenger compartment. Two pipes pass through the
bulkhead into the engine compartment and provide coolant flow to and from the matrix. The pipes from the
bulkhead are connected to the matrix, sealed with’O’rings and clamped with circular rings.
The matrix is constructed from aluminium with two end tanks interconnected with tubes. Aluminium fins are
located between the tubes and conduct heat from the hot coolant flowing through the tubes. Air from the heater
assembly is warmed as it passes through the matrix fins. The warm air is then distributed in to the passenger
compartment as required.
When the engine is running, coolant from the engine is constantly circulated through the heater matrix.
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