1998 AUDI S4 Oil

9
SSP 198/03

Cooling circuit
Both exhaust gas turbochargers are water-
cooled and integrated in the cooling circuit.
When the coolant thermostat is closed, the
coolant flows back to the coolant pump along
the short-circuit line as well as the heat
exchanger.
When the coolant thermostat is open, the
coolant flows back to the coolant thermostat
through the radiator (primary flow) or through
the oil cooler and expansion tank (secondary
flow).Located in the cooling circuit is a electrical
coolant pump.
This pump is required as a means of
protection against overheating of the coolant
under high thermal load, e.g. when the hot
engine is turned off.
Short-circuit
line
Continued coolant function pump
Heat exchanger
Coolant
Expansion
tank
Radiator fan thermoswitch F18/F54
Oil cooler
Radiator
Thermoswitch for F95
Coolant temperature
senders G2 and G62
Coolant pump

1415
SSP 198/49

Engine
Engine lubrication
The oil circuit of the 2.7-litre V6 biturbo engine largely corresponds to that
of the 3rd V6 engine generation.
In addition, the two exhaust gas turbochargers are supplied with
pressurised oil from the main oil gallery via a distributor piece. The oil is
returned directly to the oil sump.
The oil cooler was adapted to withstand the higher thermal stresses in
comparison with a naturally aspirated engine.A new feature of the biturbo is
the “integrated oil supply“ (see
next page).
to oil filter/oil cooler
Spring-loaded slipper
(chain tensioner)
Main oil gallery
Oil retention valves
Bypass valve
Filter element
Bearing cap
Oil groove
Oil temperature
sender
Oil pressure switch
Restrictor
Oil retention
valve
distributor piece

The oil circuit
A duocentric oil pump draws in the oil
through a coarse filter. Located in the
pressure chamber of the pump is a
pressure relief valve which protects
downstream components against
pressure peaks during cold starts.
The oil is fed to the oil filter via the oil
cooler. After passing an oil retention
valve, the oil flows through the filter
element. A bypass filter is connected in
parallel with the filter element.
The oil subsequently reaches the main
oil gallery. A branch line is routed to the
oil pressure control valve (clean oil
side).
The following components are supplied
with oil from the main oil gallery:
- the four crankshaft bearings
- the two exhaust gas turbochargers
via an oil distributor line
- the three pairs of piston spray jets via
a spray jet valve
- the cylinder head of cylinder bank 1
via an oil retention valve
The cylinder head of cylinder bank 2 is
supplied through a separate bore from
crankshaft bearing 2 via an oil retention
valve also.
First of all, the camshaft adjustment
valve is supplied with oil from the inlet
drilling in the cylinder head. After the oil
has passed by a restrictor, it is
channeled via the cylinder head main
gallery to the hydraulic valve tappets
and the camshaft bearings.
Exhaust gas turbocharger
Bypass filter
Oil pressure relief valve
from oil filter/oil coolerOil pressure
control valveInduction filter
Oil pressure relief valve
from oil filter/oil cooler
to oil filter/oil cooler

16
Engine
The component parts of the oil circuit
is integrated in the primary flow. By increasing
the capacity and optimising the flow
resistance, the entire oil flow can be routed
through the oil cooler. Unlike the V6 naturally
aspirated engine, a bypass is not required.
The oil cooler ......
contains an oil retention valve, the filter
element, a bypass filter and the filter bypass
valve. The latter has the task of maintaining
engine lubrication via the bypass filter if the
filter element becomes clogged up or if the oil
has a high viscosity.
The oil filter ......
opens up the oil flow to the piston spray jets if
the oil pressure is greater than 1.8 bar.
Reason: at low oil viscosity and low engine
speeds, the oil pressure would otherwise drop
below the minimum permissible level. That
aside, piston cooling is not necessary at low
engine speeds.
The spray jets valve ......
SSP 198/57

Oil pressure control valve
Oil pressure limiting valve
Chain guard

is an internal gear pump. It is attached to the
crankcase as a separate component.
The oil pump is designed in such a way that it
projects deep down into the oil sump and is
immersed completely in the engine oil when
the oil level is correct. This prevents the oil
pump running dry.
The oil pump, in combination with the
extremely short intake path, enables oil
pressure to build up more quickly and safely,
particularly during cold starts.
The oil pump is driven by the crankshaft by
means of a single chain.
A spring-loaded flat plate produces the
necessary tension.
A new feature of the oil pump is the chain
guard made from sheet steel. It encapsulates
both the chain wheel and the chain over a large
area.
This reliably prevents oil frothing and the
problems associated with this.
The oil pump ......

17
is a pressure relief valve. It is located inside the
oil pump housing and opens when the oil
pressure rises too high (cold start). If an
excessively high oil pressure builds up,
various component parts of the oil circuit (e.g.
oil filter, oil cooler) may be damaged. Also,
there is the possibility of the inlet and exhaust
valves opening or no longer closing, due to
“bulking“ of the hydraulic tappets. The knock-
on effect of this is that the engine can no
longer be started or cuts out.
The oil pressure limiting valve ......
regulates the engine oil pressure. It is
integrated in the oil pump housing. The oil
quantity “regulated“ by the oil pressure
control valve is fed to the suction side of the
oil pump.
This helps to optimise efficiency.
The oil pressure control valve ......
prevent the oil running out of the oil filter and
the cylinder heads and back into the oil sump
while the engine is stationary.
The oil retention valves ......
The “integrated oil supply“ ...
will also be adopted for all V6 5V naturally
aspirated engines.
Each camshaft bearing is supplied via a
drilling stemming from the cylinder head main
gallery.
The oil is fed along a bolt shaft in the bearing
cap to a transverse drilling.
A lubrication groove distributes the oil
throughout the camshaft bearing. It is no
longer necessary to run a pipe to the
individual bearing caps.
Advantages:
•
Fewer components
•
Quick and even oil supply
•
No additional installation work necessary
•
Lower cost
SSP 198/58

Cylinder head main gallery
Transverse drilling

prevent “flooding“ of the cylinder heads. At
high engine speeds, an excessively large
amount of oil enters the cylinder heads and
has to be returned to the oil sump via the oil
return drillings. The restrictors reduce the oil
flow and thereby ensure that return flow takes
place.
The restrictors ......

18
Front view of engine
SSP 198/51

Engine
Camshaft adjustment
valve N208
Knock sensor G66
Intake-air temperature
sender G42
Knock sensor G61
Hall sender G163
Charge air cooler
Charge air cooler
Oil filter
Oil pressure
switch
Air-cond. compressor
Visco fan
Alternator
Power assisted steering
pump drive

21
View of engine from left
SSP 198/53

Injector
Individual ignition coil
Pressure control valve
Prim. catal. converter
Exh. gas turbocharger
Pressure unit for
wastegate flap
Oil cooler
Oil filter
Charge air cooler

25
SSP 198/31

Pneumatically controlled systems
In the Biturbo, 4 systems are pneumatically
controlled:
•
Charge pressure control
The Motronic ME 7.1 activates the solenoid
valve for charge pressure control N75 and
regulates the charge pressure via the
wastegate.
•
Divert air control in overrun
The Motronic ME 7.1 activates the electric
divert air valve for the turbocharger and
opens the pneumatic divert air valves using
this vacuum.
•
ACF system
The Motronic ME 7.1 activates the solenoid
valve for the activated charcoal canister
and regulates the fuel vapour feed rate to
the engine via the vacuum.
•
Crankcase breather
The crankcase breather controls the return
of oil vapours to the engine via two
mechanical valves.
Solenoid valve for charge
pressure control N75
Solenoid valve for activated
charcoal canister N80
Divert air valve for
turbocharger N249
Non- return valves (ACF system)
Distributor piecePressure control valve
Non-return valve (divert
air control in overrun)
Divert air valve
(pneumatic)

For exact the line routing, please refer
to the Workshop Manual.

30
SSP 198/07

Engine
The crankcase breather ...
...comprises a distributor piece, a pressure
limiting valve, a non-return valve and the
associated hoses.
The oil vapours and “blow-by“ gases from the
cylinder heads and the crankcase converge in
the distributor piece.
The pressure limiting valve and the non-return
valve control the return of these vapours and
gases to the engine, depending on the intake
manifold pressure.
Vacuum in intake manifold:
The oil vapours and “blow-by“ gases return
via the non-return valve in the intake manifold.
charge pressure in intake manifold:
The oil vapours and “blow-by“ gases return
via the pressure limiting valve in the air
distributor.The pressure limiting valve limits the vacuum
in the crankcase. If the vacuum in the
crankcase exceeds a defined value, the
diaphragm is drawn over the connection
against the force of the spring and closes the
connection. The valve is designed in such a
way that it allows a small quantity to pass
through when closed. This prevents the engine
oil being drawn into the intake tract and has no
adverse effects on engine breathing.
Distributor piece
Pressure limiting valve
Non-return valve
The term “blow-by“ gases refers to
the gases which escape from the
combustion chamber past the piston
rings.
Connection
Diaphragm
Air distributor
to air
distributor
from
distributor
piece