1100 SERIES DIESEL TRUCK ENGINE Cooling System Caterpillar

Cooling System

The cooling system consists of the water pump, two thermostats and lines and passages to direct the coolant throughout the engine.

Coolant from the radiator bottom tank flows through two thermostats to the inlet side of the water pump. The centrifugal-type water pump mounts on the front cover and is belt driven by the crankshaft pulley. The pump has two outlets. Coolant from the outlet on the right side of the pump flows through a passage in the front cover to one side of the engine and coolant from the other outlet flows to the other side of the engine.

The coolant circulates through the block to the cylinder heads. Coolant flows from the heads through connecting sleeves to the return manifold in the front cover. Orifices in the sleeves regulate the flow from the heads.


Part of the coolant from the left bank is diverted from the block to the oil cooler. External lines direct coolant from the block, to the cooler and back to the return manifold in the front cover.

An internal passage in the front cover directs coolant from the return manifold to the thermostats. If the thermostats are closed the coolant flows to the pump and is recirculated through the engine. If they are open, coolant flows from the return manifold to the radiator and from there to the pump.

NOTE: This engine must never be run without thermostats as coolant will not circulate through the radiator and this will cause rapid overheating.

By using the shunt cooling system a positive head of coolant is maintained at the pump inlet to help prevent aeration and pump cavitation. It differs from the conventional cooling system in that the radiator top tank is divided into two compartments (upper and lower) with a small air/coolant bleed tube connecting them. A shunt line located as low as possible in the upper chamber connects it to the pump inlet.

When the coolant reaches the temperature necessary to open the thermostats, coolant is directed from the bottom of the radiator through the thermostats, water pump, engine, radiator top tank and the radiator core. Coolant (and air which might be in the system) will flow through the small air/coolant bleed tube into the upper chamber. The volume of coolant which flows through the bleed tube from the lower chamber to the upper chamber will flow out the shunt line and to the pump inlet line.

Air in the system vents through the bleed tube and remains in the upper chamber until it is vented out through the pressurized relief valve.

NOTE: The top tank temperature must never exceed 210°F (99°C).