Range Rover P38
BMW DIESEL
3
DESCRIPTION AND OPERATION
COOLANT CIRCULATION
Operation
When the engine is started from cold, the thermostat,
integral in the housing (2), prevents any coolant
circulation through the radiator by closing off the
supply from the radiator. During the engine warm up,
the water pump (4) pumps coolant around the
cylinders in the crankcase (12) and through separate
galleries to the cylinder head. At the rear LH side of
the cylinder head, a proportion of the flow is diverted
through a heater feed pipe (7). The heater feed pipe is
connected to the heater matrix (8), which is housed in
the distribution unit of the heating and ventilation
system. This coolant is then carried, via the heater
return pipe (9) back to the water pump. The remaining
coolant flows through a bypass port at the front of the
cylinder head back to the water pump to complete the
cycle.
When normal engine running temperature is reached,
the thermostat opens and a secondary valve closes
the bypass port. With the thermostat open, coolant is
circulated through the top hose (5) to the radiator.
Coolant is drawn from the base of the radiator by the
water pump. Coolant circulation through the
crankcase and cylinder head to the heater matrix
remains the same.
An integral bleed pipe (6), connects the top of the
radiator to the expansion tank and aids bleeding of air
from the coolant system. The expansion tank cap
contains a pressure valve which allows excessive
pressure and coolant to vent to the overflow pipe (11)
if the system has been overfilled.
VISCOUS FAN
The viscous drive unit for the cooling fan on diesel
engines work on the same principal as that fitted on
V8 engines but is of slightly different size.
See this
section.