Cooling System Aeration

Low coolant level in a cross flow radiator will equalize in both tanks with engine off. With engine at running 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 sucked 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.
^ Exhaust gas leaks into the coolant can also cause the same problems.