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Lotus Service Notes Section KJ
Thermostat Closed
Heater matrix Thermostat closed
circuit
By-passow
Throttle body circuit
Heat exchanger circuit
k76a
KJ.1 - GENERAL DESCRIPTION
The engine liquid cooling system comprises an engine driven water pump, flow thermostat, front mounted
radiator with two electric cooling fans, header tank, re-circulation pump, and associated plumbing.
The centrifugal water pump is mounted on the front face of the cylinder block, and is driven by the multi-
rib, serpentine auxiliary belt. The pump discharges coolant into a separate volute chamber for each of the two
cylinder banks, where, after cooling the cylinders, flow is directed upwards into each cylinder head before exit-
ing into an outlet housing bolted to the rear of the cylinder heads. From this housing, offtakes are provided for
the engine cooling radiator, heater matrix, throttle body, radiator by-pass pipe and, if fitted, an oil/water heat
exchanger. A thermostat housing is located on the timing cover above the water pump, and controls the flow
of returning coolant from the front mounted radiator.
Thermostat closed circuit (cold engine):
At coolant temperatures below 80°C (176°F) the dual valve thermostat is closed, shutting off the return
circuit from the radiator and opening a by-pass valve to admit coolant from a by-pass pipe connected to the
outlet housing on the rear of the engine. Coolant exiting the cylinder heads meets a closed radiator circuit and
is directed through four subsidiary circuits:
By-Pass: The greater proportion of flow is via the radiator by-pass pipe back to the engine side of the thermo-
stat housing.
Heater: An offtake on the engine outlet housing feeds the heater matrix via a re-circulation pump (see below),
pipework running through the RH sill, and a heater by-pass valve mounted to the left of the HVAC unit. Re-
turn pipework follows a parallel route and connects to the rear end of the heater return rail. This return rail is
routed down the 'V' of the cylinder block, alongside the by-pass pipe, and connects to the engine side of the
thermostat housing.
Throttle body: A small offtake on the outlet housing supplies a flow of hot water to the throttle body to inhibit
ice formation around the valve in severe climatic conditions. An outlet hose from the throttle body connects to
heater return rail.
Oil/water heat exchanger (if tted): On cars so fitted, an oil/water heat exchanger is fitted on the LH side of
the cylinder block and is fed with engine lubricating oil via feed and return hoses linking to the main bearing
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