Engine - Td5 (Description): Description and operation (page 7 of 7)

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/cm₂ (157 kPa, 23 psi) is experienced.