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