Did you ever have heat on a continuous basis?

Is the yellow color from rust or the color of the antifreeze?

Forgot if the engine was a V6 or 4 cyl. The V6 has an aluminum block/head, the 4 cylinder has an iron block.

If rust had not been present the flushing method would be to remove the T-stat then reinstall the housing. Use a garden hose in the upper radiator hose and let the water come out the lower hose until clear.

The 4-cylinder has drain plug behind the engine that can be reached from the driver’s side.

The V6 should have two drain plugs, one on the front drivers side the other on the drivers side of engine.

If rust you might use chemical treatments to remove it. The issue is the debris can break free and end up stuck in the radiator.

One method is to use a section of hose to connect the upper and lower radiator hoses leaving the radiator out of the loop. Remove the T-stat and let the chemical circulate in the engine. Follow the directions on the chemical bottle.

The other issue could be a head gasket problem allowing air into the coolant system. One signs of a blown head gasket are excess bubbles in the coolant. A radiator shop can test for exhaust gases in the coolant or you can buy a test kit for around $40.