cant tell you for sure, but if you pinch closed one of the soft hoses coming off the heater core and then warm the car up to normal operating temp. If only one of the lines feel hot to the touch you just found the inlet because you must have pinched the outlet because hot anti freeze isnt able to leave the heater core and heat the hose attached to outlet of heater core.
Or just pull both hoses and start car and see which hose has anti freeze coming out?
If this is all hooked up and running jim6789 first answer is a good idea.
Looking for a Used Malibu in your area?
CarGurus has 51,591 nationwide Malibu listings starting at $1,550.
Search Chevrolet Malibu Questions
Chevrolet Malibu Experts
Related Models For Sale
Used Cars For Sale