2001 Malibu overheating, coolent no ciculating

Hey guys, im 17 work down my Familes Auto Body Shop, anyways we got this 2002 Chevy Malibu down there, did some body work to the left side Fender, but we noticed that the car was very low on Coolent, the lady took her car back, and she brought it back complaining of overheating. So we added anti freeze to it(the pain in the ass car doesnt have a radiator cap) and it wont exept the water, it just keeps pushing it out through the water fill box. What the hell is the issue with this, i am familiar with the Head gasket problems and lower intake manifold gasket problems on these 3.1 V6 motors, but could it just be the thermostat not opening? or is it a clogged Radiator not allowing the fluid to ciculate. Any information on this would be much appreaciated, because we gotta get this car back to the owner, and make it so she down gotta go to a mechanic and get charged for this, but we dont mechanics. Thanks for your time.

Could be an air bubble causing the overheating.

the bleeder is on the left above the water pump.

thanks, i'll deff try that.