Get a radiator/cooling system leak tester kit to pressurize and locate the source of the leak if that's the case. I have the kit below and it helped me find a pinhole leak on a small hose below the heater core hoses. https://www.amazon.com/8MILELAKE-Radiator-Pressure-Tester-Cooling/dp/B01M0HDCM0/ref=sr_1_10?keywords=radiator+leak+test&qid=1559933494&s=gateway&sr=8-10
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