22
N73B60 Engine - Diagnosis
Coolant Circuit
The coolant flow has been optimized allowing the engine to warm up as quickly as possi-
ble after a cold start as well as even and sufficient engine cooling while the engine is run-
ning. The cylinder heads are supplied with coolant in a cross-flow pattern. This ensures
more even temperature distribution to all cylinders.
The cooling system ventilation has been improved and is enhanced by using ventilation
ports in the cylinder heads and in the radiator. The air in the cooling system accumulates
in the reservoir/expansion tank. When a pressure of 2 bar is reached in the expansion tank,
the air is bled out by the pressure relief valve in the reservoir cap.
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The ventilation ports in the front of the cylinder heads provide quicker “self bleeding”
during a routine coolant exchange. The complex cooling system and the small ventilation
ports require that time should be allowed after the cooling system has been filled for the air
to escape.
Coolant flow in the Engine Block (similar to N62)
The coolant flows from the water pump through the feed pipe in the engine's V and to the
rear of the engine block. This area has a cast aluminum cover. From the rear of the engine,
the coolant flows to the external cylinder walls and from there into the cylinder heads.
The coolant then cross flows through the cylinder heads (exhaust to intake) into the engine
block inner coolant jacket into the engine “V” and through the return connection to the ther-
mostat housing. When the coolant is cold it flows from the thermostat (closed) directly into
the water pump and back to the engine (recirculating for faster warm up).
When the engine reaches operating temperature (85 ºC-110 ºC), the thermostat opens the
entire cooling circuit to include the radiator.
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