Bleeding the cooling system

O.K. I installed the flush kit on the inlet heater hose on advise from a mecanic

inorder to burb the air lock I have in the heater core.

Now how do I go about it?

I don`t need to actually flush the system

just bleed it.

I’m interested in seeing other replies. I think you can’t do what you think you are doing. Modern engines have the coolant overflow that automatically takes the air out as the engine cycles from hot to cold when driven and then parked. If getting the engine nice and hot and turning on the heat doesn’t do it, you probably have another issue like the valve that controls the hot coolant to the core or a plugged heater core. Sometimes the valve is separate and easy to change, sometimes it is part of the heater core, The heater core is almost never EASY. It often involves taking apart the dash board.
That said, you could try doing a coolant flush according to the flush kit instructions. You might clear an obstruction. Be sure to finish with the right mix of antifreeze and water. A flush and new coolant definitely can’t hurt.

What kind of car? My Honda cars have a bleed valve on the thermostat housing to allow you to bleed air out of the system quite easily. Rocketman

Air lock is a growing problem due to the complexity of the engine cooling system and the heater. The air rises and often becomes trapped in high points in the system. The flushing “T” will provide a vent for the air if installed in the correct location. Ideally, connect an air presure source regulated to under 12 psi to the overflow line at the cap and loosen fittings or open flushing “T” caps to allow air to escape.

This is on a 1997 GMC siera 5.7

See if any of the radiator filling funnels that clamp on the radiator itself aids in properly filling the cooling system. What sympton are we trying to correct? I know you write “air lock in heater core” but I want to know more.

In my experience your truck is not known to be a problem child in regards to 'air in system". The FSM does say to use the type of funnel I describe.

disconnect BOTH heater hoses at the engine. Use a garden hose to back (and front) flush the heater core. Then fill the heater by the lower (on the firewall) hose until coolant or water runs out the upper hose. Reconnect the hoses to the engine.

Get the engine up to operating temperature. With the engine idling, slightly loosen the upper radiator hose clamp. Take a flat bladed screwdriver and slip it between the upper radiator hose and hose neck on the radiator. Allow the engine to idle until all the air is purged from the cooling system. Retighten the clamp.

This is the quickest way to purge the air out of a cooling system.


Try idling with the fill cap off until warmed. Then shut the engine down to cool and top up to fill line on the overflow tank. Do this a few times. It might work; does for me with two different brands.