Discovery 2. Manual - part 98

COOLING SYSTEM - V8

DESCRIPTION AND OPERATION

26-2-5

1 Heater matrix
2 Heater return hose
3 Heater inlet hose
4 Heater inlet pipe
5 Throttle housing
6 Throttle housing inlet hose
7 Throttle housing return pipe
8 Manifold outlet pipe
9 Heater return pipe

10 Coolant pump

11 Bleed screw
12 Radiator top hose
13 Radiator bleed pipe
14 Radiator
15 Radiator bottom hose
16 Thermostat housing
17 Coolant pump feed hose
18 Expansion tank
19 Pressure cap
20 Overflow/breather pipe

COOLING SYSTEM - V8

26-2-6

DESCRIPTION AND OPERATION

Description

General
The cooling system used on the V8 engine is a pressure relief by-pass type system which allows coolant to circulate 
around the cylinder block and the heater circuit when the thermostat is closed. With coolant not passing through the 
radiator, this promotes faster heater warm-up which in turn improves passenger comfort.

A coolant pump is located in a housing at the front of the engine and is driven by a drive belt. The pump is connected 
into the coolant passages cast in the cylinder block and pumps coolant from the radiator through the cylinder block.

A viscous fan is attached by means of a nut to the coolant pump pulley drive spindle.  The fan draws air through the 
radiator to assist in cooling when the vehicle is stationary. The fan rotational speed is controlled relative to the running 
temperature of the engine by a thermostatic valve regulated by a bi-metallic coil.

The cooling system uses a 50/50 mix of anti-freeze and water.

Thermostat housing
A plastic thermostat housing is located behind the radiator. The housing has three connections which locate the 
radiator bottom hose, top hose and coolant pump feed hose. The housing contains a wax element and a spring loaded 
by-pass flow valve.

Thermostat - Main valve
The thermostat is used to maintain the coolant at the optimum temperature for efficient combustion and to aid engine 
warm-up. The thermostat is closed at temperatures below approximately 82

°

C (179

°

F). When the coolant 

temperature reaches approximately 82

°

C the thermostat starts to open and is fully open at approximately 96

°

C 

(204

°

F). In this condition the full flow of coolant is directed through the radiator.

The thermostat is exposed to 90% hot coolant from the engine on one side and 10% cold coolant returning from the 
radiator bottom hose on the other side.

Hot coolant from the engine passes from the by-pass pipe through four sensing holes in the flow valve into a tube 
surrounding 90% of the thermostat sensitive area. Cold coolant returning from the engine, cooled by the radiator, 
conducts through 10% of the sensitive area.

In cold ambient temperatures, the engine temperature is raised by approximately 10

°

C (50

°

F) to compensate for the 

heat loss of 10% exposure to the cold coolant returning from the bottom hose.

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 at idle, 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 coolant through the heater matrix to improve passenger comfort 
in cold conditions.

When the engine speed increases above idle 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 engine's cooling needs at higher 
engine rev/min.

COOLING SYSTEM - V8

DESCRIPTION AND OPERATION

26-2-7

Inlet manifold - Cooling connections
Coolant leaves the cylinder block via an outlet pipe attached to the front of the air intake manifold. The pipe is 
connected to the thermostat housing and the radiator by a branch hose off the radiator top hose.

Hot coolant from the engine is also directed from the inlet manifold via pipes and hoses into the heater matrix. Coolant 
is circulated through the heater matrix at all times when the engine is running.

A further tapping from the inlet manifold supplies coolant to the throttle housing via a hose. The coolant circulates 
through a plate attached to the bottom of the housing and  is returned through a plastic bleed pipe to an expansion 
tank. The hot coolant heats the air intake of the throttle housing preventing ice from forming.

An Engine Coolant Temperature (ECT) sensor is fitted in the inlet manifold adjacent to the manifold outlet pipe. The 
sensor monitors coolant temperature emerging from the engine and sends signals to the ECM for engine 
management and temperature gauge operation.
 

 + 

 ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine 

management.

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 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 opens at a pressure of 1.4 bar (20 
lbf.in

2

) 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 away 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 into the passenger 
compartment as required.
 

 + 

 HEATING AND VENTILATION, DESCRIPTION AND OPERATION, Description.When the engine is 

running, coolant from the engine is constantly circulated through the heater matrix.

Radiator
The 45 row radiator is located at the front of the vehicle. The cross-flow type radiator is manufactured from aluminium 
with moulded plastic end tanks interconnected with tubes. Aluminium fins are located between the tubes and conduct 
heat from the hot coolant flowing through the tubes, reducing the cooling temperature as it flows through the radiator. 
Air intake from the front of the vehicle when moving carries heat away from the fins. When the vehicle is stationary, 
the viscous fan draws air through the radiator fins to prevent the engine from overheating.

Two connections at the top of the radiator provide for the attachment of the top hose and bleed pipe. A connection at 
the bottom of the radiator allows for the attachment of the bottom hose to the thermostat housing.

Two smaller radiators are located in front of the cooling radiator. The lower radiator provides cooling of the gearbox 
oil and the upper radiator provides cooling for the engine oil.
 

 + 

 MANUAL GEARBOX - R380, DESCRIPTION AND OPERATION, Description.

 

 + 

 AUTOMATIC GEARBOX - ZF4HP22 - 24, DESCRIPTION AND OPERATION, Description.

 

 + 

 ENGINE - V8, DESCRIPTION AND OPERATION, Description.

Pipes and hoses
The coolant circuit comprises flexible hoses and metal formed pipes which direct coolant into and out of the engine, 
radiator and heater matrix. Plastic pipes are used for the bleed and overflow pipes to the expansion tank.

A bleed screw is installed in the radiator top hose and is used to bleed air during system filling. A drain plug is fitted 
to each cylinder bank in the cylinder block. These are used to drain the block of coolant.

COOLING SYSTEM - V8

26-2-8

DESCRIPTION AND OPERATION

Coolant pump

1 Pulley flange
2 Body
3 Impeller

4 Gallery
5 Inlet connection

The coolant pump is attached to the front of the cylinder block with nine bolts and sealed between the pump housing 
and the cylinder block with a gasket. The pump comprises a shaft which passes through an alloy housing. The outer 
end of the shaft has a flange which allows for the attachment of the pump drive pulley which is secured with three 
bolts. The drive pulley is driven by the grooved auxiliary drive belt and rotates at the same speed as the crankshaft. 
The inner end of the shaft is fitted with an impeller which draws coolant from the thermostat housing and circulates it 
through the galleries in the cylinder block and through the heater matrix.

The shaft is supported on bearings in the housing which are packed with grease and sealed for life. A seal is 
positioned in the housing to further protect the bearings from the ingress of coolant. The seal is manufactured from a 
synthetic material which will allow for expansion of the casing when hot coolant is present.

 The cast alloy housing has a hose connection which provides the attachment for the coolant pump feed hose. The 
cast housing connects with galleries in the cylinder block and distributes coolant from the pump impeller into the 
galleries and water jackets.