Low Coolant Level - Symptoms and Causes

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:
^ Transmission oil will become hotter.
^ High reading shown on the temperature gauge.
^ Air in the coolant can cause loss of flow through the heater.
^ Exhaust gas leaks into the coolant also can cause the same problems.

DEAERATION
Air can only be removed from the system by gathering under the pressure cap. On the next heat up it will be pushed past the pressure cap into the Coolant Recovery System (CRS) tank by thermal expansion of the coolant. It then escapes to the atmosphere in the CRS tank and is replaced with solid coolant on cool down.