The cooling system maintains engine temperature at an efficient level during all engine operating conditions.

A thermostat controls coolant circulation. The thermostat remains closed until the engine reaches normal operating temperature. When the engine is cold, coolant does not circulate through the radiator. This allows for faster engine warm-up. When the engine reaches normal operating temperature, the thermostat opens, and the coolant circulates through the radiator in order to keep the engine from overheating.

The L67 (VIN 1) engines have a closed cooling system. This means you can add coolant to the coolant recovery reservoir without removing the pressure cap from the radiator.

On the L47 (VIN C) engine, remove the surge tank pressure cap in order to add coolant.

The engine-mounted water pump is belt driven. Coolant from the radiator outlet flows to the water pump inlet, and the coolant is pumped through coolant passages in the engine block and into the cavities surrounding the cylinders. Coolant then flows through holes in the cylinder head gaskets into the cylinder head coolant passages.

Passages in the intake manifold direct the coolant to the thermostat. When the thermostat is closed, the coolant is prevented from returning to the radiator, and the coolant is recirculated for quick engine warm-up.

When the engine reaches operating temperature, the thermostat opens, and the coolant flows to the inlet tank on the top left side of the radiator. The coolant is cooled as the coolant flows across the horizontal core tubes to the outlet tank on the right side of the radiator. This completes the coolant flow cycle.

In the L47 (VIN C) cooling system, the water pump takes coolant from the radiator and passes the coolant through the thermostat on the inlet side of the pump. The coolant enters the block at the rear of the engine from the crossover. The coolant is then routed through the cylinder heads back to the crossover. At this point the coolant has the following 4 possible routes:

Both of the cooling systems (L67 and L47) are sealed by a pressure type radiator filler cap which causes the system to operate at pressures higher than atmospheric pressure. This higher pressure raises the boiling point of the coolant and increases the cooling efficiency of the radiator.