How you check for an air lock in the cooling system of a 940 Volvo?

To check for an air lock in the cooling system of a Volvo 940, start by inspecting the coolant level in the reservoir; it should be at the proper level. With the engine cold, remove the radiator cap and start the engine, allowing it to reach operating temperature while observing for bubbling or gurgling sounds, which may indicate trapped air. You can also squeeze the upper radiator hose to help release any air bubbles. If the coolant level drops significantly, top it off and repeat the process until the air is purged.