Installed an after market radiator fan in 2013 Elantra. Replaced thermostat and radiator cap. Overheating after running for 30 minutes at idle. No coolant loss. Mechanic says only possibility is Hyundai doesn't like the after market fan. No sounds or leaking at water pump and no signs of head gasket problems. Is this realistic? Mechanic claims fan turns on when it's supposed to. Thinking maybe the high speed relay. Maybe only low speed fan is coming on and when idle needs high speed. Any thoughts or suggestions would be appreciated