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Q: Coolant leak from a black box (HVAC box)?

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Hi my name is ray. I need advise on 78 mark 5. it has coolant leak between the black box(HVAC box)and the fire wall. I didn't open the box yet but it starts leak when I turn on the heater so I just guessing it is heater core or the piping concerned. I just want to stop the leak so I'm planning to by pass the piping. It will cause only no heater? If it is leaking form the heater core, It will solve the problem?

The most likely cause of your leak is the heater core inside of the car’s heater case. The leak will come out of the A/C’s drain. If you are going to bypass the heater core then I would recommend connecting the two hoses together or just running a new hose from one pipe to the other pipe on the engine. This will ensure the coolant circulates through the water pump and cooling system well. The heater core can be replaced at any time in the future. If you need some assistance with this, consider YourMechanic, as one of our mobile technicians can come to you to diagnose the coolant leak and help you install a new heater hose to ensure good coolant circulation.

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