Cooling System Aeration

Low coolant level in a cross flow radiator will equalize in both tanks with engine off. With engine at running and at operating temperature, the high pressure inlet tank runs full and the low pressure outlet tank drops. If this level drops below the top of the transmission oil cooler, air will be drawn into the water pump:
^ Transmission oil will become hotter.
^ High reading shown on the temperature gauge.
^ Air in the coolant will also cause loss of flow through the heater core.
^ Water pump seal may run dry, increasing the risk of premature seal failure.
^ Exhaust gas leaks into the coolant can also cause the same problems.