Lotus 2004 Eleven Service Notes page 288

Lotus Service Notes
KH.1 - GENERAL DESCRIPTION
The engine cooling system comprises an engine driven water pump, a front mounted radiator with elec-
tric cooling fan(s), a header tank, re-circulation pump and associated ducting, pipework and controls.
The centrifugal water pump is mounted on the front face of the cylinder block, and is driven by the smooth
'back' side of the multi-rib auxiliary drive belt. Water is discharged from the pump into the front of the cylinder
block, around the cylinder liners and up into the cylinder head, before exiting the engine via an outlet spigot on
the rear of the head.
Radiator open circuit:
From the main outlet on the rear face of the cylinder head, a moulded hose connects with the main
radiator feed pipe which runs inside the left hand chassis side rail, before feeding the front mounted radiator.
The engine cooling radiator is of aluminium construction with plastic end tanks and is horizontally mounted on
top of the glass fibre composite 'crash structure' which also serves as a duct to direct airflow from the body
nose air intake, to the underside of the radiator. Twin 100 mm diameter electric cooling fans are fitted to the
underside of the radiator to supplement, when required, the ram air flow, and a moulded deflector panels direct
air exhausting from the top of the radiator through outlet grilles in the front bonnet. On cars equipped with air
conditioning, the condenser is sandwiched between the radiator and crash structure, with the cooling fans
attached to underside of the condenser.
The right hand, outlet spigot on the radiator feeds a return pipe routed down the inside of the chassis right
hand side rail, which is then connected to the thermostat housing on the left hand side of the block. Coolant
flowing through the open thermostat enters the water pump to commence another circuit.
Heater circuit:
A second outlet spigot on the rear of the head is used to supply the heater circuit. Water flows via a re-
circulation pump, into an aluminium pipe routed along the outside of the right hand chassis siderail, within the
composite sill member. The front end of this pipe rises over the end of the scuttle, penetrates the plenum/
scuttle baffle panel, and connects to the heater matrix mounted in the chassis front climate chamber. The
heater return circuit is similarly routed along the left hand side of the chassis, to join a steel heater return pipe
at the back of the cylinder head, and running beneath the inlet manifold to the engine side of the thermostat
housing.
In conditions of 'heat soak', after stopping a hot engine, the re-circulation pump is energised under engine
ECU control to pump coolant through the heater circuit and limit the potential for localised boiling within the
cylinder head.
Radiator by-pass circuit:
When the thermostat is closed, the radiator return circuit is shut off, and coolant leaving the cylinder head
is forced to flow through a by-pass circuit which links the engine outlet hose to the header tank and then to the
heater return pipe.
Header tank:
The top RH spigot on the header tank is connected to an air bleed on the back of the cylinder head; the
top rear spigot to the engine outlet hose; and the bottom port to a hose joining the heater return pipe immedi-
ately before its termination at the thermostat housing.
Throttle body and oil/water heat exchanger
The throttle body is water heated to prevent icing, drawing a supply from the back of the cylinder head,
and returning via an in-line thermostat, into the heater return pipe. On cars not fitted with front mounted air/oil
coolers, an oil/water heat exchanger is sandwiched between the oil filter and cylinder block. Coolant is fed
from a water jacket spigot on the left hand side of the cylinder block into the exchanger, with the outlet pipe
connecting into the heater return pipe.
KH.2 - MAINTENANCE
Under normal operating conditions, the engine cooling system, being a closed circuit, should not require
any topping up between services. As a precaution however, every week, the level of coolant in the engine
cooling header tank should be checked. The header tank is mounted at the left hand side of the engine bay,
with a hose from its underside connecting with the heater return rail near the thermostat housing. An air bleed
hose connects the header tank air space with the radiator by-pass circuit and a cylinder head spigot at the front
end of the inlet manifold. The tank is fitted with a 110 kPa (15 lb/in²) pressure cap to raise the boiling point of
the coolant to over 120°C. The transluscent header tank is marked with both cold and hot level indicators. The
Section KH
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