Discovery 2. Manual - part 405

ENGINE - TD5

DESCRIPTION AND OPERATION 12-1-17

1 Full-flow filter housing
2 Thermostat
3 Roll-pin
4 Port – feed line to turbocharger
5 Outlet port from full-flow filter (> 74

°

 C)

6 Inlet port to full-flow filter
7 Outlet port from full-flow filter (< 74

°

 C)

The main filter is a conventional full-flow cartridge-type filter containing a paper element able to trap particles greater 
than 15 micron (0.015 mm) in diameter.

The cartridge is screwed to an adaptor casting by way of a hollow brass threaded insert which connects the filter outlet 
port to the adaptor casting. A sealing ring seals the union between the oil filter cartridge and the adaptor casting.

ENGINE - TD5

12-1-18 DESCRIPTION AND OPERATION

Oil filter housing thermostat

1 Circlip
2 Thermostat end cap
3 Oil seal
4 Thermostatic valve
5 Return spring
6 Oil filter housing
7 Threaded insert

The oil filter housing contains a thermostatically controlled valve to control the direction and proportion of oil flow 
through the oil cooler matrix. When the oil temperature is cool, the centre spindle of the thermostatic element is 
compressed. In this condition the valve completely seals the passage to the turbocharger feed tapping and flow is 
directed through the oil filter adaptor housing, passing from the outlet of the full-flow filter to the cylinder block via the 
rear oil return gallery in the oil cooler housing. A proportion of the oil flow from the right hand filter outlet port is passed 
through  to the oil cooler matrix to supply the turbocharger oil feed line.

When the oil temperature rises, the heated wax in the thermostat causes the thermostat centre spindle to rise and 
push against the housing end cap, compressing the valve spring further and so opening the valve. In this condition 
oil flow from the outlet side of the full-flow filter is allowed to pass directly to the turbocharger oil feed line and reverses 
the flow through the oil cooler matrix, which now delivers a proportion of cooled oil flow to the cylinder block via the 
outlet port at the right hand side of the oil cooler housing.

The following table indicates approximate values for thermostat plunger travel against temperature:

The filter canister contains a by-pass valve which opens when the engine is cold or if the filter becomes blocked. The 
by-pass valve opens when a pressure drop of greater than 1.6 kg/cm

2 

 (157 kPa, 23 psi) is experienced.

Thermostat plunger travel mm (in.)

Oil temperature 

°

C

0 (0)

< 74 

°

C

5 (0.20)

80 

°

C

12 (0.47)

90 

°

C

16 (0.63)

130 

°

C

ENGINE - TD5

DESCRIPTION AND OPERATION 12-1-19

Oil Pressure switch

The oil pressure switch is located in a port on the outlet side of the oil cooler housing. It detects when a safe operating 
pressure has been reached during engine starting and initiates the illumination of a warning light in the instrument 
pack if the pressure drops below a given value.

Crankshaft, sump and oil pump components
The crankshaft, sump and oil pump components are described below:

Sump
The sump is a wet-type, of aluminium construction and is sealed to the engine block by means of a rubber gasket and 
twenty fixing bolts. The four bolts at the gearbox end of the sump are longer than the other sixteen bolts.

The sump gasket incorporates compression limiters (integrated metal sleeves) at the bolt holes, which are included 
to prevent distortion of the gasket when the sump to cylinder block bolts are being tightened.

The oil drain plug is fitted at the bottom of the oil sump reservoir. An oil return drain pipe is also attached to the oil 
sump which returns oil from the centrifugal filter.

Stiffener Plate
The stiffener plate assembly provides lower engine block rigidity and utilises dowels to align it to the bottom of the 
cylinder block.  A rotary oil pump is integral with the stiffener plate and an oil pick-up and strainer assembly is fitted 
to the underside of the stiffener plate. The stiffener and oil pump assembly is secured to the cylinder block by 22 bolts.

ENGINE - TD5

12-1-20 DESCRIPTION AND OPERATION

Oil pump

1 Stiffener plate
2 Ring dowel
3 Outlet port
4 Outer rotor
5 Inner rotor

6 Spring dowel
7 Oil pressure relief valve cap
8 Oil pressure relief valve spring
9 Oil pressure relief valve plunger

10 Inlet port

The eccentric rotor oil pump is integrated with the stiffener plate and contains no serviceable parts except for the 
pressure relief valve spring. The oil pump drive sprocket is attached to the front of the stiffener plate and is driven 
through a chain and sprocket system. 

A pressure relief valve is included at the outlet side of the oil pump to restrict oil pressure at high engine speeds by 
recirculating oil through the relief valve back around the pump to the inlet. The relief valve and spring is a plunger type. 
When oil pressure is great enough to lift the plunger, oil is allowed to escape past the plunger to relieve pressure and 
prevent further rise.

Oil is delivered to the pump from the pick-up through a channel in the stiffener plate. The outlet side of the oil pump 
delivers pressurised oil flow to the engine block main oil delivery gallery through a port in the stiffener plate.

Piston lubrication jets
Piston lubrication jets are fitted to the cylinder block to provide lubrication to the cylinder walls, and to the piston 
underskirt for cooling the pistons and lubricating the gudgeon pins. The input port to each lubrication jet mates with a 
port provided in each mounting position tapped at the underside of the cylinder block from the main oil delivery gallery. 
When oil pressure is sufficient to supply flow through the jets, oil is squirted to the inside of the cylinder walls to provide 
piston to wall lubrication and cooling and to the underside of the piston skirt at the bottom of the piston stroke (gallery 
cooled piston). The squirt jets also provide splash feed lubrication supply to the small end bearings of the connecting 
rods.

Each lubrication jet is fixed to a mounting position on the underside of the engine block by a single Torx screw.

Chain lubrication jet
A chain lubrication jet is located on the front face of the cylinder block, behind the front engine timing chain cover. The 
inlet port to the lubrication jet mates with an oil supply port from the cylinder block main oil delivery gallery. The 
lubrication jet is fixed to the front of the engine block by a single screw. Additional chain lubrication is provided by oil 
supply through a small aperture tapped from the cylinder head oil delivery gallery.