The contact owns a 2014 Ford Escape. The contact stated that the heater occasionally failed to function as needed. The contact added coolant to the reservoir and the heater started to operate as needed. The contact stated that the following day the failure recurred. The contact repeated the process of adding coolant 6 more times. There was no warning light illuminated. The contact stated that after repeating the process the 6th time while driving 35 MPH, the engine started overheating. The vehicle was towed to an independent mechanic and the mechanic performed a pressure test but had not found an oil or coolant leak. The independent mechanic performed other tests but was unable to determine the cause of the failure. The local dealer was contacted; however, the vehicle was not repaired. The manufacturer was made aware of the failure. The failure mileage was approximately 80,323.