Lubrication system

7.22.1 Lubrication system

From the sump reservoir under the crankshaft oil is

7.21.4 Cooling fault diagnosis

drawn through a strainer into the pump. Oil pumps

table I have an output of tens of litres per minute and

operating pressures of over 5 bar at high speeds.

A pressure relief valve limits the pressure of the lubrication system to between 2.5 and bar 2 . This

Symptom Possible faults

Suggested action

Overheating Lack of coolant

Top up but then

control is needed because the pump would pro-

check for leaks

duce excessive pressure at high speeds. After leav-

Thermostat stuck

Renew

ing the pump, oil passes into a filter and then into a

closed

Electric cooling fan

Check operation of

main oil gallery in the engine block or crankcase.

not operating

thermal switch

Drillings connect the gallery to the crankshaft

Blocked radiator

Renew

bearing housings and, when the engine is run-

Water pump/fan

Check, adjust/renew

ning, oil is forced under pressure between the

belt slipping

rotating crank journals and the main bearings.

Loss of coolant Leaks

Pressure test when

The crankshaft is drilled so that the oil supply

cold and hot, look for leaks and repair

from the main bearings is also to the big end

as required

bearing bases of the connecting rods.

Engine does not Thermostat stuck in Renew

The con-rods are often drilled near the base so

reach normal the open position

that a jet of oil sprays the cylinder walls and the

temperature or it

underside of the pistons. In some cases the con-

takes a long time

rod may be drilled along its entire length so that oil from the big end bearing is taken directly to the gudgeon pin (small end). The surplus then

7.21.5 Cooling fault diagnosis

splashes out to cool the underside of the piston

table 2

and cylinder.

The camshaft operates at half crankshaft speed,

Symptom Possible cause

but it still needs good lubrication because as the high pressure loads on the cams. It is usual to

Overheating Low coolant level (maybe due to a leak) Thermostat stuck closed

supply pressurised oil to the camshaft bearings

Radiator core blocked

and splash or spray oil on the cam lobes. On over-

Cooling fan not operating

head camshaft engines, two systems are used. In

Temperature gauge inaccurate

the simplest system the rotating cam lobes dip into

152 Advanced automotive fault diagnosis

a trough of oil. Another method is to spray the oil pump. This is normally on the end of the oil cam lobes with oil. This is usually done by an oil

pick-up pipe. An extra filter is also used that stops pipe with small holes in it alongside the camshaft.

very fine particles. The most common type has a The small holes in the side of the pipe aim a jet of

folded, resin impregnated paper element. Pumping oil at each rotating cam lobe. The surplus splashes

oil through it removes all but smallest solids over the valve assembly and then falls back into

from the oil.

the sump. Most engines use a full-flow system to filter On cars where a chain drives the cam, a small

all of the oil after it leaves the pump. The most tapping from the main oil gallery sprays oil on

popular method is to pump the oil into a canister the chain as it moves past or the chain may sim-

containing a cylindrical filter. From the inner ply dip in the sump oil. Figure 7.52 shows a typ-

walls of the canister, the oil flows through the fil- ical lubrication system.

ter and out from the centre to the main oil gallery. Full-flow filtration works well provided the filter is